Aspects of the Population Dynamics of

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Aspects of the Population Dynamics of Sympatric Map Turtles, Graptemys
barbouri and Graptemys ernsti, in the Lower Choctawhatchee River System of
Alabama and Florida
A Thesis
Presented to
The Faculty of the College of Arts & Sciences
Florida Gulf Coast University
In Partial Fulfillment
Of the Requirements for the
Degree of Master of Science
By Christopher J. Lechowicz II
APPROVAL SHEET
This thesis is submitted in partial fulfillment of
the requirements for the degree
of Master of Science
__________________________________
Christopher J. Lechowicz II
Approved:
_________________________________
Dr. Jerome A. Jackson
Professor of Ecological Sciences
Florida Gulf Coast University
Committee Chair/Advisor
_________________________________
Dr. James Locascio
Research Scientist
Mote Marine Laboratory and University of South Florida
________________________________
Dr. Donald Duke
Professor of Environmental Studies
Florida Gulf Coast University
Name: Christopher J. Lechowicz II
Date of Degree:
Institution: Florida Gulf Coast University
Major Field: Ecological Sciences
Major Professor: Dr. Jerome Jackson
Title of Study:
ASPECTS OF THE POPULATION DYNAMICS OF SYMPATRIC MAP TURTLES,
(GRAPTEMYS BARBOURI AND GRAPTEMYS ERNSTI) IN THE LOWER CHOCTAWHATCHEE
RIVER SYSTEM OF ALABAMA AND FLORIDA.
Pages in Study: 105
Candidate for Degree of Master of Science Environmental Science
Table of Contents
Acknowledgments……………………………………………………………………………………….VI
Abstract………………………………………………………………………………………………….VII
Introduction………………………………………………………………………………………….…..…1
Species Description……………………………………………………………………………….……6
Barbour’s map turtle (Graptemys barbouri)……………………………………………….……..6
Escambia map turtle (Graptemys ernsti)…………………………………………………………7
River Description………………………………………………………………………………………9
Cryptic Species………………………………………………………………………………………..11
Choctawhatchee Conundrum………………………………………………………………………….13
Objectives………………………………………………………………………………………………..16
I. Basking Surveys………………………………………………………………………………………...17
Methods…………………………………………………………………………….………………….17
Results…………………………….…………………………………………………………………..19
Discussion……………………………………………………………………………………..……...20
II. Range Determination…………………………………………………………………………………...25
Methods………………………………………………………………………………………………..25
Results……………………………………………………………………………...…………………28
Discussion……………………………………………………………………………………...……..32
III. Morphological Differentiation……………………………………………………………………...…35
Methods……………………………………………………………………………………………..…35
Results…………………………………………………………………………………………………40
Discussion…………………………………………………………………………………………..…44
IV. Biogeographical Considerations and Potential Origin of these Turtles in the Drainage…………...…49
Methods……………………………………………………………………………………………..…49
Results……………………………………………………………………………………………...…50
Discussion………………………………………………………………………………………….…55
Future Research……………………………………………………………………………………………59
Conclusions……………………………………………………………………………………………..…60
Literature Cited……………………………………………………………………………………………64
Figures…………………………………………………………………………………………………..…70
Tables……………………………………………………………………………………………………...87
Graphs……………………………………………………………………………………………………104
ACKNOWLEDGMENTS
I thank the Alabama Department of Conservation and Natural Resources (ADCNR) and the
Florida Fish & Wildlife Conservation Commission (FFWCC) for issuing permits for this study. I
thank Jim Godwin from ADCNR for his guidance and support with the study. This discovery
was his baby and he was cooperative and humble in helping me, the first person, besides himself,
to work on Graptemys in this river system. I thank Dr. Craig Guyer from ADCNR for allowing
me access to the Pea River specimens in the Auburn University Museum. Thanks to my primary
advisor Dr. Jerry Jackson for being patient with me and pushing me when I needed a push. I also
thank my other two committee members (Dr. James Locascio and Dr. Donald Duke) for
providing both expertise in the scientific method and advice in scientific writing. I appreciate the
advice and data provided by George Wallace, Kevin Enge, and especially Jeff Lovich. Special
thanks to my employer, the Sanibel-Captiva Conservation Foundation, for allowing me time off
work to perform this study as well as to the SCCF Marine Lab for use of their jon-boat and 15 hp
engine. I thank the Chicago Herpetological Society, the Explorer’s Club of Southwest Florida
and Graptemys.com for financial assistance that allowed me to do this work.
Of course, none of this would have been possible without the help of my field crew. I thank
Bill Love and Daniel Parker for their volunteer time in the field. Most of all, I thank my good
friend, John Archer, for the time he spent with me in the field on his own dime. I thank my
loving wife for always supporting me and “watching over the ranch” while I was gone catching
turtles. Last of all, I thank the Chicago Herpetological Society, for taking my love of herpetology
as a teenager and guiding it in a positive direction, and my mentor and one of my greatest
friends, Ron Humbert, who taught me nearly everything I know about map turtles and river
biology at a young age. Ron, this is for you.
vi
Abstract
The first instance of sympatric megacephalic map turtle species (Graptemys barbouri and
Graptemys ernsti) along the Gulf Coast of the United States, and below the fall line, is in the
Choctawhatchee River system in Alabama and Florida. This unique population was discovered
in a river system that was believed to be devoid of Graptemys species. Barbour’s map turtle (G.
barbouri) was discovered and documented in 1997 and the Escambia map turtle (G. ernsti) in
2002 in the Pea River, a western tributary of the Choctawhatchee River by James C. Godwin.
From 2007-2008, I collected data from basking surveys and capture efforts along the
Choctawhatchee and Pea rivers in Alabama and Florida. I found data from basking surveys
reliable in the Choctawhatchee River for identifying Graptemys down to species, but not in the
Pea River, because of the overlap in range and the presence of hybrids. This project began as a
mark-recapture study at five locations but was converted to a survey and mark endeavor up the
southern Choctawhatchee and Pea rivers in Alabama, as well as the northern Choctawhatchee
River in Florida. The discovery of putative hybrids of these species by James Godwin added an
additional layer of complexity to this new range extension. Godwin included a general range
map based on a low number of captured specimens in his unpublished report on the range of G.
barbouri in this drainage in Alabama, presenting the occurrence of both species in the river
system. I provide an updated range map of both species in the river system, as of 2008, including
delineation of a hybrid zone where specimens with shared morphological traits have been
observed.
I captured 115 Graptemys specimens and measured carapace length, plastron length, carapace
width, height, weight and head width on each in the field. All turtles were marked, and released
back at the point of capture. I also measured 8 specimens from the Auburn University Museum.
vii
Of these 115 turtles I captured, I classified 72 as G. barbouri and 38 as G.ernsti. The remaining 5
turtles with morphological traits of both species, at a ratio of nearly 1:1, were labeled hybrids.
All five of these apparent hybrid turtles were either juvenile or older females. No male hybrids
were found.
Morphological characteristics of G. barbouri and G. ernsti from the Choctawhatchee River
system, such as head and carapace markings, were compared with specimens from neighboring
river systems. Turtles that were considered hybrids shared near equal characteristics of both
species or had jumbled/indistinguishable patterns. The pigment widths on the upper and lower 5th
marginal scutes in G. barbouri from the Choctawhatchee river were compared with specimens
from the parent drainages and were found to be significantly different. Comparisons of relative
carapace height and relative carapace width, using the Mann-Whitney U Test, of G. barbouri and
G.ernsti from the Choctawhatchee River system and the parent drainages were not significant
among adult and subadult males and females, but were significant in unsexable juveniles.
Comparisons between G. barbouri and G. ernsti from the hybrid zone and outside the hybrid
zone in the Pea and Choctawhatchee rivers were also tested, using the same non-parametric test,
and were not significant at any size (juvenile, male, or female). Juvenile hybrid relative carapace
lengths and relative carapace widths were also compared with juvenile G. barbouri and G. ernsti
in the drainage and hybrid carapace measurements were significantly closer to G. ernsti than G.
barbouri.
I concluded that stream capture is the most plausible hypothesis for a sympatric distribution
of G.barbouri and G.ernsti in the Pea River. This explanation assumes that G. ernsti was present
in the Pea River (previously a tributary of the Yellow River) when it was captured by the
Choctawhatchee River. This connection allowed G. barbouri to enter the Pea River and expand
viii
its range upriver. G.barbouri may have entered the Choctawhatchee River from the
Chattahoochee River in Alabama or from the Chipola River in Florida by stream capture or by
brief connections of close neighboring tributaries. Basking and capture data from the
Choctawhatchee River, south of the Alabama border, shows a much higher abundance of G.
barbouri, as opposed to upriver of the confluence of the Pea River, where stream capture was
originally suspected.
ix
Introduction
Map turtles [Genus Graptemys] are the most diverse group of turtles in North America. With
14 species (and two subspecies), this freshwater turtle group is known for its proclivity to river
endemism. Although not all species are river-drainage specific, most are endemic to one or two
river systems, especially along the Gulf Coast. This model closely follows the diversity and river
drainage-specific endemism of freshwater fishes (Swift et al. 1985). Ten of the 14 species are
river-system endemics of southeastern rivers that empty into the Gulf of Mexico. These forms
occupy specific rivers found from the Apalachicola River in Florida to the Guadalupe River in
Texas.
Map turtles are named so because of the intricate pattern on the carapace (and plastron in
some species, i.e. G. sabinensis, G. caglei, G. versa) that often resembles a topographical map.
These “maps” vary in color, shape, and pattern. Patterns are more pronounced in juveniles and
generally become less evident in most adults. However, males tend to retain the “map-like”
pattern more readily than females. The carapace of large female Graptemys gets very worn down
and often dull in color due to their tendency to hide under large stumps, crevices in dead trees,
and rocks along the banks of rivers.
The shape of the carapace in Graptemys is very distinctive. Most species show some type of
knobby projections or spikes down the vertebral scutes (scutes 2-4). This trait is at its extreme in
the southeastern United States with the sawback group. The sawback group (G. flavimaculata, G.
nigrinoda, and G. oculifera) consists of three microcephalic species found in river systems in
Alabama (Alabama River), Louisiana (Pearl River), and Mississippi (Pearl, Pascagoula, and
Escatawpa rivers). The extremely knobby or sharp projections on the carapace of hatchlings of
1
most other species become less obvious with age (Cagle 1954). The pulchra-group (G. barbouri,
G. ernsti, G. gibbonsi, G. pearlensis, and G. pulchra) are a megacephalic group of turtles that
also have spike-like or knobby projections on the vertebral and marginal scutes, although theirs
are not as pronounced (Lovich and McCoy 1992). These five species are found in river systems
in Georgia (Flint, Chattahoochee), Alabama (Alabama, Yellow, Conecuh, and Choctawhatchee
rivers), Florida (Apalachicola, Chipola, Escambia, and Choctawhatchee rivers), Mississippi
(Pascagoula, and Pearl rivers) and Louisiana (Pearl River). Three of the five species in the
pulchra-group are sympatric with each of the three species of the sawback group in their
particular river drainages.
Sexual dimorphism is extreme in map turtles. Males are much smaller than females. Adult
male G. barbouri reaches an approximate carapace length of 115 mm (135 mm maximum),
while adult females have an average carapace length of about 264 mm (330 mm maximum;
Sanderson 1974). An adult female can be 4-5 times the mass of an adult male, such as in G.
barbouri (mean value of 206 g in males and 2500-3300 g in females; Sanderson 1974). Juvenile
map turtle growth rates are very high during the first couple of years (45% a year in plastron
length until they reach 100 mm and then it slows to almost 0%) and then decrease considerably
as they reach maturity, Sanderson 1974; Ernst and Lovich 2009). Males mature at around 3-4
years and females at 14-20 years (Sanderson 1974). When a female reaches full adult size,
growth all but ceases (Sanderson 1974). Indeterminate growth was once believed to occur in all
reptiles, but now it is known that this trait only occurs in certain individuals and not populations
(Congdon 2012). Male map turtles do not show plastron concavity as in many other turtles. They
do, however, have a longer, thicker tail and a more posteriorly positioned cloaca as compared to
females. Head width is also a dimorphic trait in members of the pulchra-group (G. barbouri, G.
2
ernsti, G. gibbonsi, G. pearlensis, G. pulchra), and G. geographica. The megacephalic head of
an adult female G. barbouri is unmistakable as compared to that of a male. This widened head
helps the turtle consume hard-shelled mussels and clams with the help of an enlarged alveolar
surface in the mouth (Figure 1). The alveolar surface enables the turtle to crush hard mussels,
clams, and snails (Lindeman 2000).
Megacephaly and microcephaly in map turtles pertains to the width of the head of adult
females only. Female Gulf Coast map turtles feed primarily on hard-shelled prey such as
mussels, clams, and snails. Their strong and immense alveolar plate enables megacephalic
female map turtles to crush and consume bivalves (Lindeman 2000). Consequently, a large
female map turtle has a very large, sometimes distorted head shape that differs considerably from
the head of a smaller male. Female sympatric microcephalic species have a head size more in
proportion to their body without an enlarged alveolar surface. In other words, they resemble
larger versions of the male turtles. Microcephalic females primarily eat insects, snails, and other
small hard- and soft-bodied invertebrates. By the female having a different head size and
therefore feeding on different prey, the sexes are less likely to compete for food resources. Both
species of map turtles involved in this study are megacephalic.
Graptemys habitat is mostly riverine (moving water), although creeks, streams, oxbow lakes,
and even some isolated lakes may contain them (Ernst and Lovich 2009). These turtles are avid
baskers that spend many hours of the day lying on woody debris, rocks, or manmade debris
while taking advantage of the heat and ultraviolet light from the sun (Sanderson 1974). When
disturbed, they quickly plunge from their perch and hide among a maze of twisted branches near
the bottom of the river. I will refer to such partially or fully submerged collections of woody
vegetation as deadwood, brush piles, or “stick-ups”.
3
Deadwood basking areas are the result of fallen trees in the river channel, especially in sharp
bends. These dead trees have submerged and exposed sections. Map turtles use the exposed parts
to sun themselves for thermoregulation, prevention and destruction of parasites and fungi (that
may grow on their skin or carapace), and for exposure to ultraviolet radiation which facilitates
absorption of vitamin D (Prichard and Greenwood 1968). Map turtles may spend 6 or more hours
a day basking (Sanderson 1974). The submerged part of deadwood is used for protection and
feeding. When turtles are startled, they dive off the exposed basking areas and hide themselves
among the twisted, submerged parts of the tree. Many invertebrates also use the submerged logs
as habitat and turtle forage on the attached invertebrates. Many freshwater clams wedge
themselves into the deadwood along the bottom of the river. Female map turtles often hide in the
deeper parts of the river with deadwood and can feed on these invertebrates without going into
open water. Males often search along the smaller branches near the surface of the water where
the light allows algae to grow along the wood. Many soft-bodied invertebrates (such as the larvae
of dragonflies and damselflies (Ephemeroptera), caddisflys (trichopterans) and snails) live
among these algae-laden branches.
The number of map turtles that can be seen during basking surveys is a function of the
abundance of deadwood along a river channel (Lindeman 1999). Without basking areas, map
turtles can be very hard to be seen and identified. Major storm events, such as tropical storms
and hurricanes, create more map turtle habitat by knocking more trees into the water (Lechowicz
2005). Deadwood breaks down over time due to decay and becomes either totally submerged
and/or is pushed down river There are more basking sites (deadwood) generally in curves and
turns in the river because free-moving deadwood gets caught up in banks. Along with more
abundant basking sites in curves of the river, exposed open sand areas are common. Sandbars
4
along steep curves in the river are advantageous nesting areas because hatchlings have more
habitats there to hide in after entering the river.
Both incubating and hatchling map turtles are preyed upon by a diversity of aquatic and nonaquatic animals. Raccoons (Procyon lotor), opossums (Didelphis virginiana), and armadillos
(Dasypus novemcinctus) are the main mammalian predators on Graptemys eggs (Ernst and
Lovich 2009). Fish crows (Corvus ossifragus) are equally detrimental to nests. They watch the
female deposit her eggs and fill in her nest, then, after the turtle walks away, the fish crow probes
into the nest with its bill to retrieve the eggs, one at a time. Once in the water, hatchling map
turtles are eaten by fish such as bass (Micropterus sp.) and gar (Lepisosteus sp.). It is
advantageous to have more deadwood (brush piles) in an area. Fewer brush piles results in
hatchling turtles being forced into high density groups in the limited habitats. Large fish,
American alligators (Alligator mississippiensis), and alligator snapping turtles (Macrochelys
temminckii) also use these deadwood piles for refuge. Close proximity of hatchling turtles and
large predators in deadwood is counterproductive to high hatchling survival rates (Lechowicz
2005).
In northern climates, map turtles brumate (hibernate) over the winter, underwater, in the
river or stream (Ultsch et al. 2000). In southern climates, they remain active most of the winter,
but, as poikilotherms, are slowed down by cooler water temperatures. In Florida and southern
Alabama, they can be seen basking every month of the year, if it is warm enough. As a general
rule, basking occurs if the air temperature is higher than the water temperature (Humbert pers.
comm.). However, they are most active from late March to mid-October (Humbert pers.
comm.).
5
Species Descriptions
Barbour’s map turtle (Graptemys barbouri)
Barbour’s map turtle (Figure 2) is a large basking turtle (Family Emydidae) with extreme
sexual dimorphism. Males reach about 130 mm CL (carapace length) and females can reach 330
mm CL. G. barbouri has a vertebral keel with black spines that become worn down with age,
especially in females. Individuals of both sexes are mostly tan or gray with yellow to orange
markings on the skin and carapace.
On top of the head, G. barbouri has a mask-like pattern that consists of two postorbital
blotches connecting one interorbital blotch (Figure 3). There is a dark “Y-shaped” patch between
the postorbital blotches (Figure 4). G. barbouri has a transverse bar on the chin (Figure 5), a
feature only shared with one other Graptemys species, G. sabinensis from Louisiana and Texas.
G. barbouri also has a “U-shape” pattern that opens posteriorly behind the transverse bar (Figure
6). The “U-shape” may have connections to other striping or not. The neck and limbs have both
wide and narrow yellow stripes.
The carapace of G. barbouri can have pronounced to subtle yellow or orange patterns. The
second and third costal scutes, on each side of the carapace, have a “C” shape (Figure 7) that is
often distorted or faded in large females. The markings on the upper 5th and 6th marginal scutes
appear as a thin or bold capital letter "C" or an upside down "L" whose vertical bar is closest to
the anterior part of the scute (Figure 8). Also, there may be nondescript half-circles, or a faint
lower case "c" inside of the large "letter C" and/or a small filled circle but this trait is more
common in G. ernsti. The 5th and 6th lower marginal scutes also have a “C” pattern, but that
6
pattern can also resemble an “H” or “I” (Figure 9). This yellow to orange color occupies 50% or
more of the visible scute. The interior of this “C” pattern also may have smaller “C” patterns.
Barbour’s map turtle occurs in the Apalachicola River system in Alabama, Georgia, and
Florida (Figure 10). This includes the Chattahoochee, Flint, and Chipola rivers, and many of
their tributaries. It has recently been found in small numbers in the Wacissa (Jackson 2003), and
Ochlockonee Rivers (Enge and Wallace 2008) in north Florida; its presence there is probably as
a result of human releases. G. barbouri is most associated with limestone-bottomed sections of
rivers.
G. barbouri is protected throughout its range. It is state listed as Endangered in Alabama
(Mirarchi et al. 2004) and Florida (“Barbour’s map turtle: Graptemys barbouri” 2013) and as
Threatened in Georgia (Jensen et al. 2008). It is protected from any type of take, collection, or
commercialization. The Florida Natural Areas Inventory Listing is G2 or Imperiled (global and
state). The IUCN (International Union of the Conservation of Nature) lists G. barbouri as LR/nt
(LOWER RISK/near threatened). All Graptemys spp. are listed by CITES (Convention on
International Trade in Endangered Species of Flora and Fauna) as Appendix III (van Dijk 2011).
Escambia map turtle (Graptemys ernsti)
G. ernsti (Figure 11) is a large basking turtle (Family Emydidae) that shows extreme sexual
dimorphism. Males reach 132 mm in CL and females can reach 285 mm. Like G. barbouri, they
are also tan to gray with yellow to orange marking on the skin and carapace in both sexes. In
G.ernsti, the two postorbital blotches are not connected to the interorbital blotch (Figure 12).
Most specimens also show supraoccipital spots at the ends of the paramedial neck stripes (Figure
13). G. ernsti also has a nasal trident on the upper surface near the tip of their snout (Figure 14).
7
The chin is not as distinctive as in G. barbouri. This species usually has three spots or blotches
along the anterior edge of the chin and variable partial “U-shaped patterns posterior to them that
are extremely variable (Figure 15a-b). There is not a transverse bar under the chin.
The marginal scute pattern of G. ernsti is somewhat similar to that of G. barbouri. The upper
marginal scute pattern can appear as a thin capital letter "C" or upside down "L" whose vertical
bar is closest at the anterior part of the scute (Figure 16). There are usually nondescript halfcircles, or a faint lower case "c" inside of the large "letter C" and/or a small a small filled circle.
The lower marginal scute has a much wider bar. This large bar begins anteriorly and occupies
nearly 50% of the scute, although it is normally located along the outside edge of the scute
(Figure 17). The color of these bars tends to be yellow as opposed to orange in G. ernsti. The
yellow color on the marginal scutes is usually consistent with that of all the patterns on the scutes
of the carapace.
The pleural (costal) scutes (second and third only) of G. ernsti differ slightly from those of G.
barbouri in having a thin yellow to orange “C”-like pattern. The “C’-like pattern on the second
pleural scute usually has an intersecting line that begins mid-“C” and progresses anteriorly until
it reaches that end of the scute (Figure 18). Variation in this characteristic is common, but the
pattern itself is usually very thin and mostly or partially vanishes as the turtle approaches
adulthood.
The Escambia map turtle is found in three river systems, the Escambia (named the Conecuh
in Alabama), the Yellow, and the Choctawhatchee river systems (Pea River only; Figure 19).
The Escambia/Conecuh and Yellow rivers originate in Alabama and empty into Escambia Bay in
the Florida panhandle. G. ernsti is not found in the Blackwater River, which is between the
8
Escambia and Yellow rivers, and empties into Escambia Bay. The Blackwater River is named so
because it is what is known as a “blackwater river” – its waters are acidic, dark, and “tea-like” in
color resulting from its heavy load of tannins from decaying vegetation. The prey items of
female megacephalic Graptemy, freshwater clams, mussels, and snails, are less abundant in
blackwater rivers for various reasons. Snails require high calcium content in water bodies to
build their shells and blackwater rivers have very low calcium. Also, high vegetation content
(decaying) in blackwater rivers are counterproductive to bivalve abundance and diversity. G.
ernsti is most associated with sandy bottoms, occasionally with gravel bottoms.
G. ernsti is protected throughout its range from take, collection, and commercialization. It is
listed as Endangered in Alabama (Mirarchi et al. 2004) and protected from any type of collection
and take in Florida (due to its similarity to G. barbouri; “Freshwater turtles” 2009). There is a
possession limit of two per person from animals not collected from the wild. The Florida Natural
Areas Inventory Listing is G2 or Imperiled (global and state). The IUCN lists G. ernsti as LR/nt
(LOWER RISK/near threatened). All Graptemys species are listed by CITES as Appendix III
(van Dijk 2011a).
River Description
The Choctawhatchee River is a major alluvial river between the Yellow and Apalachicola rivers
in Florida (Figure 20, rivers map). It is a south-flowing river that begins in Henry and Dale
counties in Alabama and empties into Choctawhatchee Bay along the Florida panhandle in
Walton and Okaloosa counties. The river is approximately 227 km (141 miles) long and begins
in two tributaries (named the East Fork and West Fork) in Henry and Dale counties in Alabama.
9
The Choctawhatchee River has a main tributary to the west called the Pea River that is
approximately 248 km (154 miles) long. The Pea River is actually longer in river kilometers than
the main stem of Choctawhatchee River (if you do not include the East and West forks that
converge to form the headwaters). The Pea River begins in Bullock County, Alabama, and
converges with the Choctawhatchee River in Geneva, Alabama. The Pea River is peculiar in that
the southern section of the river shifts from northeast to southwest in direction to northwestsoutheast. As the Pea River approaches the Florida state line, it turns sharply east and one small
1.8 km (1.1 mile) dip enters Florida and then reenters Alabama (Figure 21). It is called the Pea
River because of its pea soup color (green) most of the year.
The riverine habitats along the Pea and Choctawhatchee rivers in south Alabama and in Florida
are similar in appearance, except for width. The Choctawhatchee River along the Florida border
averages about 70 m across, whereas the Pea River averages about 35 m across near the Florida
border (Godwin 2002). There is more shading of the Pea River by trees due to its intrinsic
narrowness as opposed to the Choctawhatchee River. I noticed that south of the confluence with
the Pea River, the banks of the Choctawhatchee River get a lot of uninterrupted sunlight, as trees
are not able to stretch across the river like a canopy. The riverine forest canopy trees are
primarily sweetgum (Liquidambar styraciflua), red maple (Acer rubrum), American sycamore
(Platanus occidentalis), bald cypress (Taxodium distichum), and American beech (Fagus
grandifolia). The dispersion of tree species along the bank depends on the relative height of the
land along the river. Bald cypress and red maple are common in lower areas, whereas American
sycamore and American beech are in the higher areas.
I found that both rivers had occasional sand bars along the banks where turtles will nest. I
found sand bars to be more frequent in bends on the Pea River and in straightaways on the
10
Choctawhatchee River (Figure 22). My study areas on the Pea River had many more turns and
curves, as opposed to the mostly straight sections I surveyed on the Choctawhatchee Rivers. The
lengths of the sandbars were greater on the Choctawhatchee, as opposed to the Pea River. These
two rivers change in flow quite often from rainfall (or the lack thereof) to the north. It is not
uncommon that sandbars become completely submerged due to high flows. There are numerous
sections of the Pea River north of Samson, Alabama where both banks of the river are lined with
large rock formations (that can resemble tunnels) and therefore provide little area for nesting.
Cryptic Species
As advancements in genetics over the past two decades have increased, the numbers of newly
named species have also increased. When considering Gulf Coast Graptemys species, certain
statements regarding their range and sympatric/allopatric relationships are considered mutually
exclusive. These “rules” or tendencies were thought to be infallible. The first rule is that Gulf
Coast map turtle species are endemic to one or two river systems (or to a common Bay; Lovich
and McCoy 1992). Second, if a river system supports two sympatric species, then the species are
of opposite head type (megacephalic vs. microcephalic). Third, if there is only one Graptemys
species inhabiting a Gulf Coast river system, it is a megacephalic or mesocephalic species
(females only). A species with a mesocephalic head type, such as G.caglei, is intermediate
between microcephalic (narrow) and megacephalic (wide) head width. Female mesocephalic
Graptemys have head widths that are noticeably wider than that of microcephalic species, such
as G. nigrinoda, but not as exaggerated as a megacephalic species such as G. barbouri.
The recent discovery of cryptic species has resulted in the identification of further diversity
of Graptemys species (Lovich and Gibbons 1997, Ennen et al. 2010). In the last 20 years, G.
11
pulchra has been separated into three species (G. ernsti, G. gibbonsi, G. pulchra) (Lovich and
McCoy 1992) and G. gibbonsi has been separated into 2 species (G. gibbonsi and G. pearlensis)
(Ennen et al. 2010). Differences between G. pulchra (pre-1992) have been noted by previous
Graptemys researchers (Cagle 1952, Mount 1977). The division of G. pulchra into three species
kept G. pulchra as an Alabama River drainage endemic, G. ernsti in the Escambia and Yellow
river systems (both emptying into Escambia Bay) and G. gibbonsi in the Pearl and Pascagoula
river systems. This split was based on mostly morphological and geographical differences. The
morphological differences among these three species are distinct. However, the naming of G.
gibbonsi, as one species, from the Pascagoula and Pearl rivers was due to the lack of substantial
noticeable morphological differences between turtles from the two river drainages.
In 2010, G. pearlensis was named from the Pearl River in Mississippi (Ennen et al. 2010). The
naming of this species separated G. gibbonsi into two species (G. gibbonsi from the Pascagoula
River and G. pearlensis from the Pearl River). This was based on genetic, morphological, and
geographical characteristics. The genetic study showed conclusive evidence that these two
species that were more divergent than the two sympatric microcephalic species, G. flavimaculata
(from the Pascagoula River) and G. oculifera (from the Pearl River). However, the
morphological differences are minute, considering other Graptemys species recognition traits. As
a result, positive identification, to the species level, of all individuals from a large, mixed group
from both river systems cannot be differentiated by morphological characters alone. The trend of
higher priority of species identification by genetic sampling rather than morphological
characteristics is still questioned and misunderstood by many people. It is hard for those to
accept a new species based upon genetics alone (something you can’t visualize in a wild
specimen) without having defined diagnostic patterns, colors or body structure.
12
Choctawhatchee Conundrum
In 1996, Jim Godwin (2002) from the Alabama Department of Natural Resources was
conducting turtles surveys, for Macrochelys temminckii (alligator snapping turtle), on the
Choctawhatchee River in Alabama and saw what he believed was a Graptemys turtle. This was
the first known report of a map turtle from the Choctawhatchee River system. Godwin returned
to the area in September 1997 and documented the first G. barbouri from the river basin. He also
returned in 1999 - 2002 to collect more data (collection of specimens and basking survey data)
on this new discovery. This left many researchers puzzled as to how this species could have
been overlooked, for a century or more, in a major drainage.
On 31 May 2002, Godwin collected the first G. ernsti in the Pea River (Godwin 2002). This
was the first instance of two Gulf Coast megacephalic Graptemys species being documented in
the same river system. During his surveys, Godwin reported that G. ernsti was seen only in the
Pea River (a western tributary of the Choctawhatchee River), whereas G. barbouri had been
documented in both the Pea and Choctawhatchee rivers. In the Pea River, he also found
specimens that did not key out to either species definitively. Godwin deduced that there must be
some hybridization between the species. They were referred to as “putative hybrids” since only
morphological characters were used to identify them. Genetic analysis would have to be
conducted in order to call them true hybrids. In 2006, the first phylogenetic analysis using
mitochondrial DNA from G. barbouri, G. ernsti, and G.barbouri x G. ernsti putative hybrids
(McHenry et al. 2006) was conducted. They found that putative hybrids from the Pea River were
indeed true hybrids carrying alleles of both species. The hybrids lined up more with G. ernsti in
the phylogenetic tree than with G. barbouri, but had some unexplainable outliers that needed to
13
be explained at a later time. As of 2013, a new genetic and taxonomic assessment study on these
turtles has been conducted (Godwin et al. ms) and will soon be published.
The detection of two Graptemys species, plus putative hybrids of those species, in the
Choctawhatchee River system led to several theories as to their only recent discovery (Godwin
2002). When reports broke of the diversity within the Graptemys in the Choctawhatchee, it might
have been reasonable to assume that it came about as a result of a recent human introduction. For
many researchers, it was difficult to conceive that two Graptemys species could have been
overlooked, until 1997 and 2002, in such a large drainage. Looking back for previous work in the
drainage led to very few examples. Only a few turtle surveys were conducted in the
Choctawhatchee River in Alabama in the 1960’s, but no Graptemys were documented (Godwin
pers. comm.). With the fairly recent discoveries of low numbers of G.barbouri in the
Ochlockonee (Enge 1996) and Wacissa rivers (Jackson 2003) – allopatric to their main
population in the Apalachicola and Chipola river drainages -- it is reasonable to assume that
Graptemys could be found in adjacent drainages. The populations of G. barbouri found in rivers
east of the Apalachicola River (Ochlockonee and Wacissa rivers) are believed to be the result of
human introductions (Enge and Wallace 2008). This assumption is based on captures occurring
near frequently used boat ramps and in low numbers. This project will compare any similarities
with these believed manmade introductions to rivers east of the Apalachicola River with
Graptemys populations in the Choctawhatchee River.
Another question that arose after this discovery was the possibility of a new, undiscovered
species in the drainage. The last Graptemys species to be described (without dividing a species
into several species) was G. caglei, in 1974, from the Guadalupe River in Texas (Haynes and
McKown 1974). Several cryptic species (hidden species that had been unrecognized within
14
another species) have been described since 1974, from species that were known from multiple
river systems (Lovich and McCoy 1992; Ennen et al. 2010). These new species were described
using molecular genetics, morphology and range resulting in endemism to a particular river
drainage or bay (for example; G. gibbonsi in the Pascagoula River and G. pearlensis from the
Pearl River). According to the range patterns shown in other Gulf Coast Graptemys, a second
species occurring in a river drainage should have been of opposite head width type. Graptemys
researchers speculated as to whether or not the putative hybrids between G. barbouri and G.
ernsti were hybrids, variants of the Choctawhatchee River system, or perhaps a new
undocumented, undescribed turtle (Jackson per. comm.; Lovich pers. comm.). Morphological
inspection of suspected hybrid individuals, as in this study, would show anomalies in species
descriptions, but only genetic sampling of hybrid turtles would prove the presence of alleles of
both species.
The precise range of G. barbouri and G. ernsti in the Choctawhatchee River drainage is
unknown. Godwin included a general range map in his unpublished report (Godwin 2002) of
G.barbouri, G.ernsti, and G. barbouri x G. ernsti hybrids in this river system. This map
specified areas of the river system with G. barbouri only and areas containing both species.
There were also two locations (dots on the map) showing where hybrids were found. This map
shows that G. ernsti occupies the upper regions of the Pea River, but not farther north than Elba,
Coffee Co., Alabama, and just south of the Florida border in the Choctawhatchee River. Godwin
showed that G. barbouri has a much larger range in the drainage, occupying the entire lower Pea
River and the Choctawhatchee River to approximately 33.3 km to the north of the confluence
and 13.2 km to the south of it (within Florida). Enge and Wallace (2008, Figure 6) indicate
15
G.barbouri occurs from the confluence of the Pea and Choctawhatchee rivers south 67 km to
Ebro, Washington County, Florida.
Objectives
The objectives for this project are as follows: Basking Surveys; (1) to collect and compare
basking survey data from the Pea and Choctawhatchee rivers in Graptemys turtles per river
kilometer (#turtles/rkm or rkm) with previous surveys from this river drainage (Godwin 2002)
for similarity. (2) to compare basking survey data with neighboring river systems (parent
drainages) for similarity. (3) to assess if P. concinna is still the most frequently observed basking
turtle during surveys as reported by Godwin (2002).
Range Determination; (4) to further knowledge of the actual range of G. barbouri, G. ernsti
and hybrids in the drainage, especially where each species shows allopatry and sympatry. (5) to
create a new range map of both species in the Choctawhatchee River drainage representing data
collected during this study, as well as previous data including the delineation of a hybrid zone.
Morphological Differentiation; (6) attempt to identify similar morphological traits of
Graptemys hybrids. (7) attempt to identify morphological differences (pigment width of the
upper and lower marginal scutes, relative carapace height and relative carapace width). (8)
determine if morphological characteristics, such as relative carapace height and relative carapace
height, are different for these two species captured inside the hybrid zone as opposed to outside
in the Choctawhatchee River drainage (9) to collect the eggs from a nesting hybrid, artificially
incubate them and document the phenotypes of all offspring (whether they all or partially
resemble hybrids and/or each species).
16
Biogeographical Considerations and the Potential Origin of these Turtles in the Drainage; (10)
evaluate the credibility of human introduction, stream capture, and overland migration, as
hypotheses as to how G. barbouri and G. ernsti arrived in the Choctawhatchee River drainage.
(11) based on researched evidence, decide on the most credible hypothesis of how each of these
species arrived in the Choctawhatchee River system and how they came to be sympatric in the
system.
Basking Surveys
Field work was conducted from June 2007 through April 2009, with preliminary work in
April 2006 to assess the river and find adequate trapping locations. Data were collected during
six trips to the Choctawhatchee River drainage (Geneva and Coffee counties, Alabama; Holmes
County, Florida) during 2007-2008. Work in the field was primarily during daylight hours. I
attempted nocturnal observations and collections twice without success using the methods that
had been successful for Chaney and Smith (1950). Dip-netting and hand-capture of sleeping
specimens in brush piles at night, while using bright lights, failed due to very low river clarity.
The Pea River was not clear enough to see more than 5 cm beneath the surface in most places.
The drought conditions of 2007 resulted in their being very little deadwood clusters in water that
was deep enough to contain Graptemys and therefore made night capture useless.
Methods
A total of four basking surveys were conducted in spring and fall 2008 at two sites (two per
season). I used a 4.3 m (14-foot) flat-bottomed-boat with a 15-hp motor in conducting these.
Surveys at two sites were conducted once in spring and once in fall of 2008. All surveys were
conducted on sunny days, beginning at 12:00 p.m. A sunny day was chose in order to maximize
17
the number of turtles basking during the survey. Also, the specific start time was chosen to
maximize the amount of sunlight on both banks of the river at the time of the survey. Basking
surveys were conducted in stretches of river that allowed for continuous travel (without
bottoming out) due to low river levels. Basking surveys were not conducted in 2007 due to the
inability to launch a boat and navigate down the middle of the channel because of extremely low
river levels.
On April 20, 2008, I conducted the first survey on the Choctawhatchee River north of US
highway 2 in Florida, south of the Alabama border (30°56’53.48N, 85°50’37.91W to
30°59’35.69N, 85°49’51.16W) in an area expected to contain exclusively G. barbouri (Enge and
Wallace 2008). This survey totaled 6 river km. The second site was on the Pea River in the
hybrid zone, just south of the confluence of Flat Creek and the boat ramp at County Rd 17 to the
north, (30°59’50.88N, 85°59’52.48W to 31°0’14.22N, 86°02’28.82W). This was surveyed on
April 22, 2008. The river distance was also 6 km. Both sides of the river were surveyed. My
protocol was to spot turtles while an assistant recorded data and steered the boat down the middle
of the river. I traveled upriver while watching from the middle of the river towards shore, and
then returned downriver, watching towards the opposite shore in order to survey both sides of the
river. Effort was taken to try to equalize the speed (~ 4.8 – 8.0 kph) of upriver and downriver
travel in order to keep the sample time as close as possible. Surveys were conducted on sunny
days (little to no cloud coverage) with a range of temperature from 23.3 – 29.4° C. (74 - 85°F). If
the vessel maintained a steady course down the middle of the river at approximately the same
speed, most turtles did not dive into the water from their basking sites. If turtles on the opposite
side of the river (not the side being surveyed) were startled and jumped into the water, this could
18
create some bias. However, because of the slow speed of the boat and the 6 km distance, some
turtles would have climbed out of the river to bask again on the return trip.
Godwin (2002) and Enge and Wallace (2008) conducted basking surveys on the Choctawhatchee
and Pea rivers prior to my study. I mostly followed the same protocol (not the same routes or
distances) and found it difficult to distinguish Graptemys turtles by species on the Pea River, but
not on the Choctawhatchee River. The difference between my method and that of Godwin, Enge
and Wallace was that I traveled both upriver and downriver during the survey. I did this so I
could concentrate my attention to one side of the river at a time. With both survey routes, I was
able to navigate in the center of the river channel without causing most basking turtles to flee
from their basking logs before they could be identified. The turtles on this river were accustomed
to frequent boat travel and did not usually jump from their basking perches unless a passing boat
got too close to them (usually within 20-25 meters) or noticeably decreased acceleration adjacent
to them.
Results
In spring 2008, on the Choctawhatchee River, I observed a total of 20 G. barbouri, along with
14 P. concinna, two P. floridana, four S. minor, 12 A. spinifera, seven T. scripta, and three
unknown turtles (Table 1, Graph 1). I had high confidence in the identity of Graptemys since G.
ernsti has not been documented this far south in the drainage, as well as the captures I had made
in the area so far. The nearest documentable evidence of G.ernsti was nearly 6.44 km (4 miles)
west of the confluence of the Choctawhatchee and Pea rivers in Geneva, Alabama. This route
was repeated in the fall of 2008. Basking surveys on the 6 km stretch of river on the
Choctawhatchee River resulted in 45 G.barbouri, 21 P. concinna, three P. floridana, seven S.
19
minor, six A. spinifera, 15 T. scripta, and six unknown turtles (Table 1). Both surveys were
conducted on days when basking conditions were optimal (sunny and warm).
Basking surveys on the Pea River in the spring of 2008 resulted in observations of 19
Graptemys (unidentifiable to species), 18 P. concinna, one P. floridana, nine S. minor, two A.
spinifera, two T. scripta, and five unknown turtles (Table 1, Graph 2). The second survey in fall
2008 resulted in observations of 38 unidentified Graptemys, 16 P. concinna, two P. floridana,
six S. minor, four A. spinifera, seven T. scripta, and nine unidentifiable turtles. Both Pea River
surveys were conducted on sunny warm days when basking activity was optimal.
The 6.0-km (3.72 mile) stretch of the Choctawhatchee River, near the Alabama/Florida
border, to Route 2 in Florida had densities of 10.08 G.barbouri/km (Figure 23). The Pea River
basking surveys showed an average of 9.5 Graptemys/km in a 6.0-km section (Table 2). These
were comparable to basking surveys conducted on the Chipola River (2.64 – 5.69
G.barbouri/km; Moler 1986) if you adjusted for unknown turtles that were probably Graptemys.
Moler surveyed a 58.7 km portion of the Chipola River. Significant sections of the river had very
little basking sites so the turtle per river km was lowered. The highest average densities observed
by Moler were 13.67 G.barbouri/km in a 3.2-km section of river to 16.7 G.barbouri/km if
adjusted for unidentified turtles.
Discussion
Already being familiar with basking surveys of Graptemys turtles, I had high confidence in
positively identifying most map turtles, down to species, with binoculars. My basking surveys in
the Choctawhatchee River were successful. G. barbouri was both common and in densities
equivalent to what I have seen in the Chipola and Apalachicola rivers. However, I found it
20
difficult to correctly differentiate between G. barbouri and G. ernsti in the Pea River from the
boat. After capturing live examples from the Pea River, I decided that close examination was
mandatory to accurately differentiate between G. barbouri, G. ernsti and hybrids. For example,
some captured turtles that resembled G. barbouri lacked key characters, such as a transverse bar
and separated interorbital/postorbital blotches after close examination. Even though these turtles
were identified as a full species, due to my strict rule pertaining to a suspected hybrid having
~50% characteristics of both species, they were highlighted as questionable. When it came to
basking hatchling turtles, it was nearly impossible, even with good binoculars, to guess as to its
species. I conceded that I would need to have every turtle in my hand to make a positive
identification. This resulted is having to lump all Graptemys sightings into one group in the Pea
River basking surveys.
My previous basking survey experience in other Gulf Coast rivers, such as the Pascagoula,
Pearl, and Coosa rivers, with two sympatric species did not prepare me for the difficulty in the
Pea River. In the Choctawhatchee River system, there are two megacephalic, sympatric species,
whereas in other Gulf Coast drainages with sympatric Graptemys species, there is each of
megacephalic and microcephalic type. Rivers containing two species with opposite head width
types are fairly easy to differentiate by carapace shape (profile) and female head width because
of different diets resulting in structural differences. However, in the Pea River I found it
troublesome to differentiate between the two species, with any reliability, from a moving boat.
To differentiate, I needed to have the turtle in hand to look at morphological characteristics. As
a result, I clumped all basking Graptemys sightings together in the Pea River.
Godwin’s basking surveys in 2002 showed that G. barbouri, G. ernsti and G. barbouri x G.
ernsti hybrids (combined) were only the 2nd most abundant turtle in the Choctawhatchee and Pea
21
rivers, with Pseudemys concinna the most abundant (Godwin 2002). I found Graptemys to be
the most abundant basking turtle at those two rivers. The time of year and optimal basking
conditions may have played a part in this difference. When I conducted these surveys, hatchlings
were very plentiful and many of the observations, and captures were of hatchling Graptemys. If
hatchlings Graptemys were observed during basking surveys, but not captured in the
Choctawhatchee River, I designated them G. barbouri. However, if they were observed in the
Pea River, I called them Graptemys sp. Jim Godwin also mentioned to me in conversation that
he believes he saw a G. ernsti, in binoculars, just south of the confluence but north of the Florida
line but it cannot be verified. If this is valid, then that represents the only G.ernsti known from
the Choctawhatchee River.
Wallace conducted basking surveys for G. barbouri on the Choctawhatchee River, mostly in
Florida, and its tributaries from 1999-2001 (Enge and Wallace 2008). A 145.2-km section of the
Choctawhatchee River was surveyed resulting in an average of 5-7 G.barbouri/km (Figure 24).
These surveys were very important because it documented how far south in the drainage
Graptemys actually existed. However, particular sections of the river, especially toward the
southern-most parts of the survey (Washington County, Florida) revealed low numbers of map
turtles (Figure 24). Wallace found that G.barbouri was seen more frequently in sections of the
river with exposed limestone (Enge & Wallace 2008). Both of my basking survey zones were in
areas with limestone bottoms resulting in a high Graptemys/km. Godwin also conducted basking
surveys on the Choctawhatchee and Pea rivers in 2002 and his averages were only 0.93
Graptemys/km. This can be explained due to the fact that his numbers were averaged over long
stretches of river. Many sections of those surveys were in less suitable areas of the river or at the
outskirts of the range of these species. The Ochlockonee River basking surveys by Enge revealed
22
0.025 G.barbouri/km (Enge and Wallace 2008). This included only four G. barbouri out of the
731 other turtles that they observed during the basking surveys. All were juveniles and subadults
from nearly 35 km apart, suggesting that there may be some reproduction occurring.
Basking surveys are a common method to estimate populations of basking turtles. They are
commonly used in Graptemys population’s studies. They are not without their flaws however.
Basking surveys can be biased depending on the air temperature, water temperature and the
amount of sunlight. Turtles tend to bask when air temperatures are higher than the water
temperature. Aquatic turtles bask to increase their ambient temperature. This activity is at its
peak in the fall though spring in southern United States. When water temperatures equal or
surpass air temperatures, basking activity decreases. Aquatic basking turtles such as Graptemys.
Pseudemys, Trachemys, and Chrysemys tend to follow this pattern. Basking activity still occurs
but at lower rates than in the cooler months of the year. Graptemys turtles still need to bask, even
during the hotter months in order to dry their shells and skin to deter external parasites and
fungal infections as a result of being constantly wet. Basking activity is highest in the spring and
fall (Sanderson 1974). My basking surveys were conducted in the spring and fall to maximize
basking activity due to lower daily temperatures. While surveying on the Pea River, I noticed
that map turtles invoke a peculiar diurnal behavior when the air temperature drops below the
water temperature during cold fronts. If it is sunny and the air temperature is lower than the air
temperature, Graptemys will congregate near the surface of the water in brush piles, but will
remain submerged. It is possible that they do this to gather the ultra-violet rays from the sun by
being near the surface but remain at the highest temperature possible while staying submerged.
Turtles use UV light to process vitamin D which they get in their food. I call this “underwater
basking”. I have also seen this in south Florida with Pseudemys peninsularis. During the
23
summer, air temperature can reach around 35 degrees Celsius. P. peninsularis will bask at the
surface with just a fraction of their carapaces being above the water. This allows them to absorb
ultra-violet light by being near the surface, but keeps their body temperature low by not being
completely out of the water. Both P. peninsularis and Gulf Coast Graptemys are gathering UV
near the surface, but are submerged near the surface opposite temperature needs.
Basking surveys do not account for submerged turtles that are not basking at that time. On
the Pea River, I noticed that some brush piles did not have basking turtles even though a similar
brush pile nearby did. After years of basking surveys on other river systems, I recognized that
some deadwood piles were better than others for Graptemys. Larger turtles tend to bask on large
pieces of deadwood (Lindeman 1998) that are further from the shore and in swifter currents than
with smaller turtles. Hatchling turtles tend to gravitate closer to shore in deadwood piles with
smaller branches with very thin twigs. Both size classes of turtles prefer deadwood without green
leaves attached. When I saw an ideal deadwood pile but did not see any basking turtles I would
use a mask and snorkel and investigate the pile. Almost 50% of the time, I would see at least one
submerged Graptemys turtle. I conclude that basking surveys are only assessing part of the
population and should not be the sole method of estimating a population. Important decisions
concerning the river conservation and/or legislation in relation to Graptemys should not be solely
based upon basking survey data. At this time, there is not an efficient method to count
submerged turtles hiding in deadwood. I have had conversations with fish biologists concerning
sonar equipment that is used to survey fish and how it could be used to detect submerged turtles.
There is some promise, but it has not been tested as of yet.
24
Range Determination
Methods
Mark-recapture
Locations - In order to complete my objectives pertaining to the range of G. barbouri and G.
ernsti in the Choctawhatchee River drainage, I originally decided to conduct a mark-recapture
study to document turtle morphology, gather population data, and get a better idea of the ranges
of these two species (and hybrids) in the system. Five sites (Figure 25) were chosen to conduct a
mark-recapture study. These were: (1) the Choctawhatchee River in extreme north Florida in
Holmes County near Pittman (N3057’31.20, W8550’21.35); (2) the Pea River in south
Alabama (N3124’22.32, W8604’18.65) in Coffee County; (3) near Royal Crossroads
(N3059’41.01, W8600’55.50) in Holmes County, Florida; (4) the confluence of Flat Creek and
the Pea River (N3102’17.69, W8605’10.01) in Geneva County, Alabama; and (5) near Ganer,
Geneva County, Alabama (N3103’55.50, W8605’54.15). The mark-recapture effort was
intended to be limited to two river km at each site (1 km on each side of the point). The
reasoning for these specific sites was to include one area on the Choctawhatchee River that
contained pure G. barbouri, one area on the Pea River with pure G. ernsti, and three sites where
both species would likely be found along with possible hybrids. I chose these sites by using
Godwin’s range map (2002) and my scouting surveys in 2006 to include areas that seemed most
suitable for the species relative to their known ecology.
Field equipment and capture methods - To conduct the mark-recapture study in the
Choctawhatchee and Pea rivers, both a 4 m (14 ft) jon-boat and a 5 m (17 ft) aluminum canoe
were used. The canoe was the preferred craft for capturing turtles due to its stealth and
25
maneuverability, but it limited the distance that could be covered on the river in a day. It was
impractical to use the canoe in some stretches of the river due to the long distance between boat
ramps. The motorized jon-boat allowed large treks up and down river, but was mostly unusable
during the drought conditions of 2007.
Six primary capture methods were used, each of which was recorded for each turtle. The
methods of capture included (1) capture in a basking trap above or below water; (2) capture by
dip net from a boat; (3) capture by hand from a boat; (4) capture by hand while I was snorkeling;
(5) floating and submerged basking traps; and (6) night capture while turtles are sleeping.
Capture methods were not deployed equally, but rather by the best choice to capture turtles in a
given situation. By these capture methods, bias is certainly favorable toward younger individuals
that have not had years of experience evading predators and are therefore less skittish. A GPS
coordinate was taken at each site of capture in degrees-minutes-seconds. Each turtle was released
at the location where it was captured. The time of day of each capture was recorded in 24-hour
(military time). The time of capture was also recorded as being in one of three categories relative
to photoperiod: day (d), night (n), twilight (t). Water temperature was recorded with a laser heat
gun (Pro Exotics PE2 Infrared Thermometer Temp Gun) in degrees Celsius. The air temperature
(in degrees Celsius) was also measured using a hand-held weather meter (Kestrel 3000 Wind
Meter).
For dip-netting, I used custom-designed dip-nets with an aluminum frame measuring 45.7 cm x
45.7 cm (18” x 18” in) with a plastic net guard on the front. The pole lengths of my nets were
1.22 m (4 ft) and 50.8 cm (20 in). The 50.8 cm length handle was especially useful for capturing
juvenile turtles that were close to the vessel. The netting mesh was 6.35 mm (1/4 in) and the net
26
depth (bowl) was 10.16 cm (4 in). A shallow net bowl is preferred to limit the potential of the net
to get caught on branches in the brush pile.
Alternative protocols -Because of extreme drought during 2007, the original plan of sampling
within 2 km of the five mark-recapture sites became unrealistic. Large sections of the river had
little to no water, and we found that turtles were limited to sporadic deeper pools. The original
protocol of a mark-recapture project at five locations needed to be reworked due to a two year
field work window. After visiting all five locations in the spring of 2007, I altered my original
protocols to expand past the 2 km limit at the five chosen sites. Instead of capturing turtles at
static locations for the duration of the project, I began at my southern most site and worked my
way upriver capturing turtles sequentially.
Turtle capture began in the Choctawhatchee River at Site 1, where Graptemys were believed
to be pure G. barbouri (Godwin 2002; Enge and Wallace 2008). I sampled upriver to about 9.8
km north of the confluence with the Pea River (22.5 km total). Next, I entered the Pea River at its
confluence with the Choctawhatchee and surveyed as far north as Elba, Alabama, totaling 107
km (66.5 miles), minus a 12.3-km stretch south of the Pea River power dam, which is 8 km (5
miles) south of Elba.
Effort was given, specifically, to the Florida section of the Pea River to attempt to document
the first G. ernsti in the Choctawhatchee River drainage in Florida. A 1.77 km (1.1 mile) stretch
of the Pea River (Figure 21) dips into Florida. G. ernsti has been confirmed east and west of this
dip (in Alabama), but not actually in Florida. I also concentrated efforts in the Choctawhatchee
River, just south of the Alabama border; to try to document the first G. ernsti in Florida in the
27
Choctawhatchee River. The boundary of this effort was from the confluence of Pea and
Choctawhatchee rivers in Alabama downriver to County Road 2 in Florida. Since the main goal
was to capture a G. ernsti or a hybrid, the protocol was to capture as many examples of
Graptemys as possible. This involved concentrated capture attempts on banks with ample,
unshaded brush piles. Treks up and down the river were coordinated with the photoperiod to
allow for maximum sun exposure, since turtles rarely bask in the shade. My capture methods
used in this section of the river were by dip net and hand capture from a vessel as well as hand
capture while snorkeling. Godwin mentioned seeing a G. ernsti with binoculars, approximately 5
km south of the confluence, of the Pea River, in the Choctawhatchee River (Godwin pers.
comm.). This sighting cannot be verified and is considered undocumented.
Results
I captured 115 turtles on the Pea and Choctawhatchee rivers during this study. All turtles were
marked using the Cagle method (Cagle 1952). Turtles 50 mm or larger in carapace length were
drilled with a single hole in each pertinent marginal scute; turtles less than 50 mm were notched
on the marginal scutes. A total of 72 G. barbouri, 38 G. ernsti, and 5 G.barbouri x G.ernsti
hybrids were captured, measured and photographed, and released (Table 3). Of the 72 G.
barbouri captured, 40 (55.5%) were captured in the Choctawhatchee River and 32 (44.5%) were
captured in the Pea River (Figure 26). All G.ernsti (n = 38) captured were from the Pea River
(Figure 27), as were all hybrids (n = 5; Figure 28). Of the 115 captured turtles (Figure 29), 96
(83.5%) Graptemys specimens were unsexable and therefore considered only as juveniles or
hatchlings. Map turtles were sexable when they reached carapace lengths of approximately 72-79
mm. Of the 96 juvenile or hatchling map turtles captured, 67.8% (n = 65) were G. barbouri, 27%
(n = 26) were G. ernsti, and 5.2% (n = 5) were G. barbouri x G. ernsti hybrids (Table 4).
28
Approximately 58.4% (n = 38) of the unsexable G. barbouri (hatchlings and juveniles) were
captured in the Choctawhatchee River. The remainder (n = 27) originated from the Pea River.
All of the juvenile G.ernsti (n =26) and all hybrid map turtles (n = 5) were captured in the Pea
River. Bias toward hatchlings was certainly apparent.
As far as adults, approximately 37% (n = 7) of the 19 sexable turtles were G. barbouri and
63% (n = 12) were G. ernsti. Around 29% (n =2) of the G. barbouri were captured in the
Choctawhatchee River and the remaining (n = 5) were from the Pea River. Exactly 100% of the
G. ernsti were captured in the Pea River. Captured turtles labeled as hybrids were either females
or juveniles that appeared to be developing characteristics of females. Also, during the study
there were no recaptures of any marked turtles.
Approximately 72% (n=83) of the collected turtles were captured with a dip net. 13% (n = 15)
were captured by hand from either the jon-boat or canoe as opposed to 14.7% (n =17) captured
by hand while snorkeling in the river (Graph 3). During ideal conditions, clear and sunny and a
low river depth, underwater visibility approached 3 m. However, even the slightest bit of
precipitation would cause the water to get silty and visibility would quickly deteriorate as
described by Godwin (2002). No Graptemys were captured using basking traps (both above and
below water models) however, several T. scripta were captured with above water basking traps
above the dam near Elba, Alabama. Night capture by dip-netting or hand capture of sleeping
turtles was unsuccessful in two trials on the Pea River. Night capture was not attempted on the
Choctawhatchee River. This technique can be quite successful in rivers with medium to high
visibility (Chaney and Smith 1938), but the murkiness of the Pea River did not allow for
adequate light penetration to see the turtles.
29
Choctawhatchee River -- I surveyed the Choctawhatchee River from its confluence with the
Pea River, to 9.8 km upriver. My visual observations and captures of G. barbouri were
noticeably decreasing as I surveyed upriver. The river also began to narrow as I traveled upriver
and sunny basking areas were not as plentiful. My farthest upriver capture of G. barbouri on the
Choctawhatchee River was still 27 km shy of Godwin’s farthest capture. He mentioned that G.
barbouri numbers significantly dropped off as he traveled north on the Pea River from its
confluence with the Choctawhatchee. My findings from visual encounters and captures showed
the same trend.
Specimens (n=40) of G. barbouri that I captured in the Choctawhatchee River from County
Road 2 in Florida to 9.8 km north of the confluence of the Pea River in Alabama did not show
any head or scute pattern variations suggesting hybridization. From this limited sampling of this
stretch of river, I could not document the influence of G. ernsti in the Choctawhatchee River as
of 2008.
Pea River.--I surveyed the Pea River from its confluence with the Choctawhatchee River
to12.3 km south of the dam south of Elba, Alabama (a distance of 107 km). From its confluence
with the Choctawhatchee, all Graptemys captures and observations were of G. barbouri until the
first G.ernsti was captured at 11.4 km up the Pea River. Godwin caught one as close as 1.75 km
of north of the confluence of the Choctawhatchee with the Pea, so it is possible that G. ernsti
have entered the Choctawhatchee River, but this has yet to be documented. After the first G.
ernsti was captured at 11.4 km up the Pea River, I did not see or catch another for 3.31 km (2.1
miles) farther upriver. With this second capture of G. ernsti, capture frequency increased until
they were the dominant Graptemys species captured, in the Pea River, upstream of the
confluence with Flat Creek, but downriver of the dam near Elba. G. barbouri was the most
30
common Graptemys species in the Pea River from the confluence with the Choctawhatchee
River to 3.30 km (2.1 miles) upriver of the confluence with Flat Creek (a total of 25.5 km or 15.8
miles).
The section of the river where both species were observed at a near 1:1 ratio is approximately
10.3 km (6.4 miles) long, and extends from 30°59'40.89"N, 85°58'57.86"W to 31° 4'0.19"N, 86°
5'54.96"W. I call this the inner hybrid zone (Figure 30). The outer hybrid zone is the area outside
of the 1:1 ratio section but where hybrids have been documented as well as both Graptemys
species. This area includes G. barbouri found upriver of Flat Creek and G.ernsti found
downriver of the dip of the Pea River into Florida. The outward range of the outer hybrid zone, at
the time of this study, was from 31° 8'38.91"N, 86° 5'50.23"W to 31° 4'0.19"N , 86° 5'54.96"W
(11.8 km) and 31° 1'32.43"N, 85°52'49.64"W to 30°59'40.89"N, 85°58'57.86"W (18.2 km). In
the outer hybrid zone, it is likely that hybridization occurs but is likely less common. The total
length of the hybrid zone (inner and outer) is 36.4 km (22.6 miles). All five captured hybrids
were juveniles that could not be positively sexed; however three of them (the largest) did appear
to be developing into females because of their relatively shorter tail length and relatively wider
carapace.
On 1 September 2007, John Archer and I captured the first G. ernsti from the Florida section
(Holmes County) of the Pea River (Lechowicz and Archer 2007) with 4.5 hours of effort. I
considered it a juvenile (unsexable) because it had a carapace length of 63 mm and
indistinguishable sexual characteristics. This capture was in the outer hybrid zone where G.
barbouri is considered the more common species. Thirty-six capture hours were logged during
six trips, from June 2007 through October of 2008, in the Choctawhatchee River near the
Alabama border to try to document G. ernsti in Florida to no avail.
31
Discussion
After trying several capture methods, I found that dip-net capture and snorkeling hand capture
were the most successful for this project. Dip-net capture worked best in a canoe instead of a
motorized boat. It was easier to approach the basking turtles in the brush piles while traveling up
river. There was less noise and the turtles were less wary while using this method. There was a
bias toward hatchling-juvenile turtles while applying this method. The hatchling turtles are less
wary and resurface quicker than older animals. The older the turtle, the less likely they were to
resurface near me. Only rarely, would an adult stay visible long enough to try to net them.
Snorkeling for turtles was more biased toward adults. When a suitable deadwood pile was
spotted, I would leave the canoe or motorized boat and try to locate adult turtles in their
submerged habitat. A suitable brush pile is one that had several basking turtles on it as we
approached, that quickly dove for cover at the site of the approaching vessel. As in other
Graptemys rivers I have been on, females would seek the deepest water that contained the
biggest stumps or logs after diving in. They would either hide under submerged logs along the
bottom or go inside hollow crevices in them. Males would generally choose smaller branches to
hide under or just lay on the bottom near deadwood in less deep areas, but not shallow (less than
1.5 m). Hatchlings and juveniles prefer to hide in vast tangles of small twigs that are difficult to
enter while snorkeling.
During the drought year (2007), the motorized boat was useless. I used a canoe most of the
year and quite often there was not enough water in the river to even use that. I portaged through
many areas on the Pea River. As on the Apalachicola and the Escambia Rivers, hatchlings
emerge in late July through September. There are several waves of hatchling emergence that
appear on the river during the summer, depending on when the clutch of eggs was laid.
32
Immediately after hatching, they can be very abundant and then two weeks later they are scarce
again. A high percentage of them are eaten by predators as they are small and inexperienced in
the river. During the drought, the Pea River was reduced to mostly very shallow areas with little
to no submerged deadwood cover.
In August-October 2007, I was expecting to find numerous hatchlings but did not find any.
During my scouting trip in 2006 and while collecting turtles during the mark-recapture effort in
2008, I saw numerous hatchlings throughout the river. There were noticeable deep pools (up to
2.1 meters deep) in random locations on the Pea River in 2007. After snorkeling in these deep
pools and capturing numerous adults in the confined space, I noticed dense numbers of prey fish
(M. salmoides, L. oculatus, etc.) as well as the occasional A. mississipiensis that also used these
deep pools. Since there was little to no water in the river channel, it appeared that river fauna
crowded into these pools. Many of these pools were immediately adjacent to known nesting
beaches, but I still found no hatchlings in 2007. After inspecting a few nesting areas, I did find
some evidence of turtle hatching by seeing subtle depressions with dried up egg shells. I deduced
that the hatchlings did indeed hatch and many were probably eaten in the shallow water, by birds
or mammals, while looking for deeper water. Those that did find the pools were in close
proximity to numerous, large game fish and alligators and subsequently were eaten.
River turtle populations can survive these extremes in river level. In 2005, I conducted basking
surveys on the Apalachicola (FL), Chipola (FL), Conecuh (AL), Tensaw (AL), Coosa (AL),
Pascagoula Rivers (MS) and Pearl Rivers, during a flood period due to Hurricane Katrina. Most,
if not all, of the nesting beaches were completely submerged for long periods of time. We found
no hatchlings in the fall and saw no young turtles on these rivers in spring 2006. Occasionally,
most nests/hatchlings in an area are lost due to flooding or drought (Lechowicz 2005). The
33
flooding was so severe, that the original channels of the rivers were hard to spot from bridges.
Adult turtles were still observed from bridges at some locations during extremely high water
conditions, in the treetops, near the edges of the flooded out corridor of the rivers (Sanderson
1974; Lechowicz 2005). We did not find any Graptemys in the floodplain of these rivers where
the preferred deadwood piles were abundant.
From prior basking surveys on these seven rivers, dating back to 1994, I noticed a reduction in
the number of brush piles from year to year in surveyed stretches. Toward the early 2000’s, we
noticed a reduction in the number of hatchlings that were spotted. After Hurricane Katrina, there
was an abundance of new fallen trees in these rivers and an increased number of juvenile basking
turtles. The conclusion was that hurricanes and other severe storms are good habitat creators. By
adding wore deadwood to the river, hatchlings are able to spread out along the river, as well as
predators, causing less interaction and predation. Unfortunately, quantitative deadwood
abundance surveys were not conducted on the Choctawhatchee or Pea Rivers, but I would
predict the same results as in neighboring Graptemys rivers.
Floating basking trap efforts were unsuccessful, as far as Graptemys, even when placed directly
next to popular basking sites. The only turtle captures using floating basking traps were
Trachemys scripta. Other Graptemys researchers have good success with submerged basking
traps on other river systems. These were used infrequently during this project due to the
consistent success with the dip-net and snorkeling, plus the time it took to set them up and wait
for turtles to bask above them.
As a result of no turtle recaptures, I was unable to gather quantitative population or movement
data. However, these turtles have permanent notched or drilled carapaces. These turtles could be
34
recaptured during future studies in the river system and longevity, growth and site fidelity data
can be acquired. Because of the change from a traditional mark-recapture study at five sites to a
sequential capture, mark and move-on protocol in 2007 (due to low water levels), collected data
provided an indication of where these two species were allopatric and sympatric in the river
system.
The naming of a hybrid zone was intended to illustrate a better picture of the range of these
two species during a small time period in this drainage. However, with only 125 individuals
captured over a 23.1 km (14.3 mile) stretch in the Choctawhatchee River and a 107 km (66.5
mile) stretch of the Pea River, the graphic is not intended to be definitive. The actual range is
likely more complex than what can be shown from this study. The ranges of these two turtles are
dynamic and are likely shifting from year to year. Since G. barbouri occupies a greater
percentage of the river, it is feasible that this species could be overtaking the range of G.ernsti
(possibly due to competition). If this is valid, the expansion can only be monitored by periodic
sampling in the river using similar methods over a long period of time. From sightings and
captures during this project, G. barbouri is apparently more successful in both the Pea and
Choctawhatchee rivers than G. ernsti. The fact that G.ernsti has yet to be documented in the
Choctawhatchee River and has a smaller range in the drainage suggests that G. ernsti has not
been in the drainage as long as G.barbouri or the latter is more successful at expanding its range.
Morphological Differentiation
Methods
The morphological characteristics distinguishing G. barbouri from G. ernsti are well
documented (Lovich and McCoy 1992). They are both members of the “pulchra-complex”
(Lovich and McCoy 1992) and have the same general profile, as well as a very similar ecological
35
niche. Individuals can be identified to species by morphological characteristics or by their
genome. The characteristics used to differentiate these two species are marginal scute pattern,
chin pattern, fusion or separation of the postorbital blotches, the existence of supraoccipital
spots, and the presence of a nasal trident – a marking which resembles a pitch fork – (Table 6).
Distinguishing between species and identifying possible hybrids, in this drainage, can only be
done accurately with the animal in hand and not through binoculars.
Patterns on the upper and lower marginal scutes of these species are less distinctive than head
and chin patterns. Both species have a yellow to orange bar on the upper surface of the upper
marginal scutes with an anterior perpendicular appendage pointing towards the ventral edge of
the scute. Also, both species have a similar yellowish “C” pattern on the lower marginal scutes.
The width of this pattern is variable in both species with considerable overlap between species,
thus was not a distinctive characteristic for the animals I examined. However with a larger
sample size, a distinctive difference between species may become evident. Most diagnostic
characteristics are more distinct in younger specimens, especially hatchlings. Adult males and
subadult females are mostly differentiable as well. However, large adult females, with their more
bulbous head, tend to have characteristics that appear to be distorted in the same manner as a
design drawn on a balloon that is then inflated.
I photographed each captured animal using a Canon A95 digital camera (5 megapixel). This
camera has macro capabilities and I specifically took photos of each characteristic on each
animal. Photographs of each specimen were analyzed after field work was complete. Precise
pictures of head pattern, chin pattern, upper and lower marginal scute pattern, and carapace and
plastron were used to determine the species. Specimens exhibiting shared traits, of both species,
36
and/or jumbled traits that did not fit either species, were considered hybrids. Hybrid turtles were
examined for any similar traits among them.
Morphological characteristics from this study were compared with the same characteristics on
specimens from other river systems using data provided by Jeff Lovich, a research ecologist
from the USGS. For G. barbouri, 72 specimens from the Choctawhatchee and Pea rivers were
compared to 102 specimens from the Apalachicola River system (including the Flint and
Chattahoochee rivers in Georgia and the Chipola River in Florida). G. barbouri is the sole
Graptemys species in this drainage, so should carry one or more alleles that differ from other
species (resulting in characteristics of other species) in the samples. The presence of a transverse
bar is a key characteristic so I assumed that any specimen labeled as G. barbouri should have
one.
Lovich did not provide data pertaining to head or chin patterns in G. barbouri; however he
did provide data containing upper and lower marginal scute width and pigment width on the
lower fifth marginal scute. First, I measured the width of the upper marginal scute from the
center of the scute. Then, I measured the width of the pigmented bar that intersects that center
line. I divided pigment width by marginal scute width to obtain percentage of pigment width per
marginal scute width. I performed non-parametric statistics (Mann-Whitney U Test) to test for
differences between Choctawhatchee and parent drainages since data from other drainages did
not have a normal distribution.
I collected head pattern data from all of my captured G. barbouri (n = 72) and recorded the
presence/absence of a transverse bar under the chin. I also recorded if the interorbital and
postorbital blotches were connected (presence/absence) as well as the presence/absence of a
37
complete “Y-shaped” pattern between the postorbital blotches. G. barbouri head pattern data,
from the Choctawhatchee River, were not compared with specimens from other drainages
because this variable was not included in the data from Lovich.
For G. ernsti, 38 specimens from the Pea River were compared to 181 specimens from other
river systems; Conecuh River (Alabama), Escambia River (Florida), and the Yellow River
(Alabama and Florida). G. ernsti is the only known Graptemys species in these river systems, so
these populations should not have alleles (and therefore characteristics) of other species. The
presence/absence of a nasal trident, paramedial neck stripes with supraoccipital spots, and
separated interorbital and postorbital blotches were compared between the Choctawhatchee
River and all other river systems. Chin pattern data, which were not provided by Lovich from
other rivers, were collected and used for comparison with hybrids. This included the
presence/absence of 3-4 blotches under the chin and a complete or incomplete upside down “Ushape” posterior to the chin blotches. If the “U-shape” was branched, the number of branches
was recorded. Hybrids were also examined for all head and chin patterns found in both species.
Combinations of traits, whether combined, separate or illegible, were recorded.
I also compared two carapace dimensions of captured G. barbouri and G. ernsti from the
Choctawhatchee River drainage with specimens from parent drainages (Conecuh/Escambia
rivers for G. ernsti and the Apalachicola River system for G. barbouri). I did this comparison to
test whether the relative carapace height (carapace height/carapace length) and relative carapace
width (carapace width/carapace length) differed between the Choctawhatchee River and other
drainages. I separated all specimens, by species, into three groups (males, females, and
juveniles). Specimens that were unsexable, due to their small size, were placed in the juvenile
category. Turtles that were labeled as males showed external sexual characteristics, such as an
38
enlarged tail (thicker near the base) and a cloaca that was 1-3 cm posterior to the base of the tail.
Those turtles labeled as females showed external sexual characteristics, such as a short tail with a
cloaca near the base of the tail. Larger female specimens also showed cranial megacephaly.
I performed non-parametric statistics (Mann-Whitney U Test) on these three classes, of each
species, to test if Choctawhatchee specimens were significantly different from specimens from
the other drainages. An ANOVA or non-paired t-tests could not be used because the variances
were not equal among classes, and the data were not normally distributed (even after
transforming the data). This test was performed to find out if the measurements of
Choctawhatchee specimens were equal or similar to those in other drainages. I also compared
juvenile hybrids (n=7), five from this study and two from the Auburn Museum of Natural
History, to juvenile G. barbouri and G. ernsti from the Choctawhatchee River drainage and the
other drainages to find out if hybrids were significantly different from them.
Relative carapace height and relative carapace width of G. barbouri from the inner hybrid
zone in the Pea River were also compared to those south of the Alabama-Florida border in the
Choctawhatchee River, using non-parametric statistics (Mann-Whitney U Test), to document any
differences in G. barbouri in an area not known to include G. ernsti and an area where both
species occur in a near 1:1 ratio and therefore where hybridization is more likely to occur. A
similar comparison was done between G. ernsti from the inner hybrid zone in the Pea River and
specimens collected near Samson, Alabama, and upriver where they are thought to be pure G.
ernsti.
39
The relative carapace lengths and relative carapace widths of juvenile hybrids were compared
to those of G. barbouri and G. ernsti from the drainage to test if they were similar to either
species. These measurements were tested using the Mann-Whitney U test.
Results
The Mann-Whitney U test showed that there is significant difference (p < .00001) between the
pigment width on the upper 5th marginal scute, in G. barbouri, from the Choctawhatchee River
(CR) and the parent drainages (PD; Table 11). The mean pigment widths were 0.1111 (11.1 %)
of the total width of the scute from the CR (n =72) as opposed to 0.0851 (8.5%) from the PD
(n=92). Pigment width on the lower marginal scutes, in G. barbouri was also shown to be
significantly different (p < 0.0001) between the CR and PD (Table 12). The mean pigment
widths from the same specimens were 0.4714 (47.1%) of the total width of the scute from the CR
and 0.6108 (61.1%) from the PD.
Head patterns traits (presence of a tranverse bar, a “Y’shape” on the top of the head near the
neck stripes, and the complete connection of the interorbital and postorbital blotches) of G.
barbouri were not recorded by Lovich. However, I did collect this data from the Choctawhatchee
River specimens. A transverse bar was present in (1.000; n = 72), a “Y-shape” was present in
(0.917; n = 72), and the interorbital blotch was completely connected to the two postorbital
blotches in (0.764; n = 72) specimens.
G. ernsti head pattern traits, such as the presence of a nasal trident, the presence of
supraoccipital spots and the connection of the interorbital and postorbital blotches were
compared between the Choctawhatchee River system and parent drainages (Table 13). The
presence of a nasal trident was present in 76.3% (n = 28) of specimens from CR and 100% (n =
40
129) of the specimens from the PD. Supraoccipital spots were present in 86.8% (n = 38) of
specimens from CR and 31.0% (n = 116) from PD. Also, there was a connection between the
interorbital blotch and the postorbital blotches in 2.0% (n =38) of G. ernsti from CR and 8.5% (n
= 118) from PD.
Relative carapace height and relative carapace width are what help give Graptemys their
distinctive appearance. The “pulchra-group” and “sawback-group” of map turtles have several
architectural characteristics that separate the two groups from each other and also relate the
species within the group. The “pulchra-group”, including G. barbouri and G. ernsti, have a
higher carapace height, in general, than members of the “sawback-group”, when comparing
similar age classes. Also, the vertebral knobs or projections along the center of the carapace are
more pronounced in the “sawback group”. Still, within a group, there can be variation, such as
the noticeably lower relative carapace height in G. pulchra (pulchra-complex) from the Alabama
River drainage.
The median relative carapace height (carapace height/carapace length; RCH) of juvenile G.
barbouri from the CR was 0.9010 and 0.5437 from PR (Lovich 1992). As far as males from CR,
they showed a mean relative carapace height of 0.0453 and PD showed 0.3976. Female G
.barbouri had a CR of 0.4790 and from PD were 0.4175 RCH (Table 14). The median relative
carapace width (carapace width/carapace length; RCH) of juvenile G. barbouri from the CR was
1.016 and 0.9010 from PR (Lovich 1992). As far as males from CR, they showed a mean relative
carapace height of 0.7900 and PD showed 0.7777. Female G .barbouri had a CR of 0.8240 and
from PD were 0.7928 RCH (Table 15). The difference in relative carapace height in juvenile G.
barbouri was considered significant since the two-tailed p value is <0.001.
41
Neither male (RCH; p = 0.1698, RCW; p = 0.3800) or female (RCH; p = 0.0118, RCW; p =
0.1306) relative carapace lengths or relative carapace widths were significantly different.
As far as juvenile G. ernsti, the median relative carapace length was 0.4882 from CR and
0.5321 from PD (Table 16). The mean RCH from males was 0.4370 from CR and 0.4337 from
PD. Female RCH was 0.4460 from CR and 0.4432 from PD. The relative carapace length in
males (p =0.6239) and females (p = 0.8080) were not significantly different from the drainages,
although juveniles were considered significant (p < 0.0001). Relative carapace width in juvenile
G. ernsti was 0.9859 from CR and 0.9232 from PD (Table 17). Male RCW was 0.7884 from CR
and 0.7749 from PD while female RCW was 0.7722 from CR and 0.7730 from PD. Male were
not considered significant (RCW; p = 0.2249), as well as females (RCW; p = 0.9247). Juveniles
were considered significant (p < 0.0001).
Relative carapace lengths in juvenile G. barbouri from the hybrid zone in the Pea River were
not significantly different (p = 0.08929) from those captured outside the hybrid zone in the
Choctawhatchee River. The mean relative carapace length from the hybrid zone was 0.5461 and
0.5444 from outside the hybrid zone (Table 18). Adult males and females were not compared
due to the very low sample sizes. Relative carapace widths in juvenile G. barbouri from the same
areas were also not significantly different (p = 0.4622) with RCW of 1.010 from the hybrid zone
and 1.017 from outside the hybrid zone.
As for G. ernsti, juvenile G. ernsti captured in the hybrid zone did not significantly differ in
relative carapace height (p = 0.6563) or width (p = 0.3886) from specimens captured upriver of
the hybrid zone (Table 19). The mean relative carapace length of G. ernsti from the hybrid zone
42
was 0.5332 and 0.5296 upriver outside the hybrid zone. The mean relative carapace width of G.
ernsti from the hybrid zone was 0.9873 and 0.9751 from the same areas.
Comparisons between RCH and RCW of juvenile hybrids and both Graptemys species in the
drainage showed that hybrid carapace measurements were more similar to G. ernsti. Juvenile
G.barbouri from the Choctawhatchee River drainage had relative carapace heights that were
nearly significant (p = 0.0591) and relative carapace widths that were significant (p = 0.0018) as
opposed to juvenile G. ernsti that had relative carapace heights and widths that were not
significantly different (RCH; p = 0.3321, RCW; p = 0.1168). The mean RCH was 0.5253 for
hybrids and 0.5321 for G. ernsti from the Pea River. The mean RCW was 0.9485 for RCH and
0.9859 for RCW (Table 20).
The hybrids (Figures 31-33) I identified during this study showed some similarities to each
other. Most noticeable were the reduced postorbital blotches on the top of the head. This
similarity was most evident on the posterior section of the postorbital blotches. The postorbital
blotches were either reduced to narrow appendages (Figure 31) lateral to the body or they had
wider appendages (partially reduced) pointing posterior to the body (Figure 32). Most specimens
had reduced interorbital blotches as well. This is likely caused by the “Y-shape on the top of the
head (as in G. barbouri) being enlarged in hybrids. Neck striping was more pronounced posterior
to the lateral appendages (reduced posterior blotches). In most cases, the interorbital and
postorbital blotches were connected, although they were sometimes difficult to identify due to
extreme irregularities in shape. In most cases, hybrids had nasal tridents (as in G. ernsti; Figure
32).
43
Turtles classified as hybrids demonstrated little difference in chin patterns, and are difficult to
differentiate between non-hybrid turtles by chin pattern alone. However, chin patterns of hybrids
do have slight similarities. Like non-hybrids, they all had a complete or incomplete upside down
“U-shape” posterior to the transverse bar (G. barbouri) or 3-4 blotches (G. ernsti) or both. The
“U-shape” may be branched or not. Two hybrids and some questionable specimens found in the
outer hybrid zone had what resembled a slightly more posterior transverse bar (as in G.
barbouri), as well as 3-4 chin blotches (as in G. ernsti; Figure 31). When both characteristics
were present, the transverse bar had short, connected perpendicular bars pointing posterior to the
turtle. This made the bar resemble a very wide “U”. This wide “U-pattern could be the result of
combined chin blotches.
The scute patterns on the carapace of hybrids were indistinguishable from non-hybrids due to
both species having very similar patterns to begin with. Natural variation in both species,
especially pigment width, shape, and color on the pleural and marginal scutes, made positive
identification depend on other characteristics, such as head pattern. Hybrids did not have any
noticeable blending of scute patterns of both species. However, hybrids did superficially
resemble one species or the other when just looking at the shell of the turtle. This was not due to
carapace patterns but by profile. G. ernsti has a higher relative carapace height (profile) than G.
barbouri.
Discussion
Marginal scute pattern and pigmentation have been used to help separate multi-river drainage
Graptemys species; for example, G. pulchra was taxonomically split into three species (G. ernsti,
G. gibbonsi, and G. pulchra; Lovich and McCoy 1992) and G. gibbonsi was later split into two
species (G. gibbonsi and G. pearlensis; Ennen and Lovich 2010). Although patterns on the upper
44
and lower sides of the marginal scutes in G. barbouri are very similar in appearance, pigment
width on the upper and lower surfaces of the scutes of turtles from the Choctawhatchee River
were significantly different from scutes of the species from their parent drainages (Apalachicola
and Chipola rivers). Choctawhatchee specimens have wider pigment widths than do turtles from
the two parent drainages. I was unable to find out if this pattern also occurs in G. ernsti, because
these characteristics were not examined by Lovich on turtles from the parent drainages. I believe
that this trait likely represents clinal variation of G. barbouri in the Choctawhatchee River
system rather than an exchange of alleles between these species. Certainly this is an area for
future research.
Head and chin patterns in G. barbouri and G. ernsti are more distinct than scute patterns in
these species. Although multiple morphological characteristics are often used to identify species,
a few characters are uniquely distinct and their use can usually quicken the identification
process. For example, the transverse bar on the chin of G. barbouri is a relatively invariable
characteristic. No other Graptemys species east of the Mississippi River has this trait. G.
barbouri is often confused for other members of the ‘pulchra-complex”, but none has a
transverse bar. However, even distinct head patterns can vary in a pure population of the species,
so the accurate identity of a species must be made using a variety of characteristics (when
depending on purely morphological characteristics without a genetic component).
The separation of the interorbital and postorbital blotches in G. ernsti is another mostly
consistent characteristic. All other “pulchra-complex” species have these three blotches on the
top of the head to some extent. Rarely, one of the dark bars separating the interorbital blotch
from either of the postorbital blotches in G. ernsti may be broken; creating a very small
connection; this is uncommon in the parent drainages, but was fairly common in the Pea River
45
(especially in the hybrid zone). Other head pattern traits, such as the presence of supraoccipital
spots at the ends of paramedian neck stripes and the presence of a nasal trident in G. ernsti, are
identifying traits that are seen most of the time, (≤ 85% of the time). These traits that are absent
in over 15% of specimens from the parent drainages were found at lower percentages in hybrids.
G. ernsti can have 1-5 chin blotches. These usually roundish blotches appear to connect with
each other in some specimens, forming elongated blotches that resemble long bars. These long
bars can sometimes resemble a transverse bar, as in G. barbouri, but are found more posterior to
the traditional location of the transverse bar near the front of the chin. G. ernsti has a higher
tendency for branched “U-shaped” patterns than does G. barbouri. I found no other significant
variation in the “U-shaped” pattern on the chin of either species or hybrids. This pattern has not
been looked at in any other drainage that contains these species.
I analyzed five hybrids that I captured, one of the two juvenile specimens labeled as hybrids
from Auburn University Museum (AUM), and the two hybrid photos from Godwin’s report
(2002). I could not use one hybrid from AUM for head-pattern analysis since it was missing the
top of the head. I may have captured more hybrids than those discussed here as a result of my
rigid adherence to the arbitrary definition of a hybrid as an individual that shows an
approximately equal number of traits from each parent species. To do otherwise might have
allowed for natural variation in the population to be misinterpreted as hybridization. Among the
115 specimens I captured, 17 individuals showed characteristics suggesting they might be of
hybrid origin but did not fit my criteria. Without a genetic component to the study, it was
impossible to more accurately assess the extent of hybridization. I did take genetic samples
throughout the study and they are in a genetics paper on the Graptemys of this drainage (Godwin
et al. 2013 in review).
46
Variation in one suite of characters isn’t always accompanied by parallel variation in another
suite. For example, a questionable hybrid specimen from the Pea River (Figure 33) closely
resembled pure G. barbouri, as far as the lower profile (relative carapace height) and less pointy
snout. When I showed a profile picture of this turtle to several Graptemys researchers, without
letting them see the head and chin patterns, they said it looks like G. barbouri. However, when I
revealed the head and chin patterns, the lack of a transverse bar and the presence of the three
small blotches under the chin, as well as a nasal trident suggested that it is actually G. ernsti.
This turtle has a relative carapace height and width consistent with G. barbouri, but head and
chin marking mostly consistent with G. ernsti. This specimen clearly appears to have alleles of
both species. This turtle would likely be misidentified as a pure G. barbouri during a basking
survey (even at close range) and in hand (if the ventral side of the turtle was not checked).
Relative carapace height and relative carapace width of male G. barbouri and G. ernsti from
the Choctawhatchee River were not significantly different from the same parameters of the
species from the parent drainages. I expected females to show the same pattern, but G. barbouri
females showed a significantly higher relative carapace height in the Choctawhatchee, while G.
ernsti females showed no significant difference in relative carapace height between river
systems. The small sample of adult females from the Choctawhatchee River included only one
large adult (n=5; range of carapace lengths = 72-286 mm), whereas the greater sample from the
parent drainages included many larger adults (n=38; range of carapace lengths = 67.7-296.0
mm). Thus while the significance level suggests that higher RCH might be a trait of
Choctawhatchee River system specimens, there may be ontogenetic factors that are confounding
the situation. Both species showed significant differences in juvenile relative carapace height and
relative carapace width. G. barbouri and G. ernsti from the Choctawhatchee River had higher
47
RCH and RCW than juveniles from the parent drainages. This may be due to lower flow rates in
the Pea and Choctawhatchee rivers. Turtles in rivers with higher average flow rates tend to have
lower carapace height (such as in G. pulchra) in the Alabama River; flow rate = .83 ft/sec; USGS
2013), and higher carapace height (such as in G. gibbonsi in the Pascagoula River; flow rate =
0.67 ft/sec; USGS 2013). A higher carapace height is counterproductive to turtles in rivers with
high currents, especially smaller turtles. Juvenile Graptemys in the Choctawhatchee River
system may have higher relative carapace heights because they do not need to swim against
currents as strong as in the parent drainages. It is advantageous to have a higher relative carapace
height and width, as juveniles, to prevent from being eaten by many fish and birds. Relative
carapace heights and widths in adult Graptemys from the Choctawhatchee River were similar to
those in the parent drainages, with the exception of relative carapace height in female G.
barbouri. A lower relative carapace height makes the older and larger age class more
hydrodynamic in high river current.
Within the Choctawhatchee River there were no differences in RCH and RCW between
samples from within and outside of the hybrid zone. This suggests that hybridization may not
affect carapace dimensions. Since hybridization is more likely in the hybrid zone where both
species are near a 1:1 ratio, I would have expected a difference because alleles of both species
are likely shared there. Perhaps with a larger sample size, a difference would have been evident.
Relative carapace height in juvenile G. barbouri from the Choctawhatchee River drainage
was very close to being significantly greater from the RCH of hybrids. However, relative
carapace width of G. barbouri was significantly greater than the RCW of the hybrid juveniles.
The relative carapace height and width of juvenile G. ernsti from the Pea River were not
48
significantly different from those of hybrids. This means that juvenile hybrids more resemble G.
ernsti, in profile, than G. barbouri.
Biogeographical Considerations and Potential Origin of these Turtles in the
Drainage
Methods
I evaluated the credibility of three hypotheses as to how G. barbouri and G. ernsti became
established in the Choctawhatchee River system. The first hypothesis (1) was that both species
were intentionally introduced by humans. This hypothesis includes the possibility that the
release was meant to create a new population or just relocated without the intention of starting a
new population. In considering this hypothesis, I looked at the full geographic range of both
species in the drainage and estimated their populations by using the basking survey data per river
km.
The second hypothesis (2) assumes that G.ernsti was established in the Yellow River drainage
first, and a branch of that river (known as the Pea River) was captured by the Choctawhatchee
River (Godwin 2002). This capture would allow G. barbouri to enter the Pea River and work its
way upriver while incidentally producing hybrids with G. ernsti. I provide a map showing the
possible route of the original “Pea River” and how far it would have moved to be captured by the
Choctawhatchee River (Figure 34). Also included in that map are the opposing river directions of
three neighboring three rivers systems (Escambia/Conecuh, Yellow, and Apalachicola) along the
Gulf Coast with that of the Pea River. I also measured the closest distances from adjacent parent
river systems to the Choctawhatchee River system to document the distance turtles would have
had to travel overland (Figure 35-36). Faunal populations, such as fish and freshwater
49
clams/mussels were also compared from the Choctawhatchee and Yellow rivers to document if
they shared many of the same species, especially rare species.
The third hypothesis (3) involves turtles moving across land during flood events and/or sea
level rise. This circumstance involves G.barbouri entering a creek or stream of the
Choctawhatchee River from the outer tributaries of the Chattahoochee River during flooding
events or during Pleistocene high water periods. As far as G.ernsti, this species would have
entered a western tributary of the Pea River from a far eastern tributary of the Yellow River also
during extreme flooding. I measured distances between the outer tributaries of adjacent river
systems to the Choctawhatchee River system as evidence for the viability of overland travel as a
possible means of migration.
Results
Three hypotheses by which G. barbouri and G. ernsti could have arrived in the
Choctawhatchee River were looked at in depth. G. barbouri is known to occur in 100.3 river km
(62.3 river miles) in the Choctawhatchee River and 64 river km (39.7 river miles) in the Pea
River (a total of 164.3 km or 102 river miles). G. ernsti is known to occur in 96 river km (59.7
river miles) in the Pea River (this study and Enge et.al 2008, Godwin 2002). G. barbouri has a
much larger range in the drainage (about 68.3 river km or 42.4 river miles larger) than G .ernsti
and densities from all (this study and Enge et al. 2008, Godwin 2002) basking surveys and
captures likely represents a higher quantity of G. barbouri per river km.
I found G.barbouri to not be continuous throughout the drainage. G. barbouri is unknown
from nearly 40 km (24.9 miles) south of Ebro, Florida, to the Gulf of Mexico and over 50 km (31
miles) to the north of Godwin’s furthest upstream capture. G. ernsti is not common upstream of
50
the dam, which acts as a barrier to upriver travel, near Elba, Alabama. Only one G. ernsti has
been documented north of the dam (Godwin, pers. comm.) The Pea River continues well over
40 river km (24.9 river km) upstream of the G.ernsti capture near Elba. The lack of optimal
habitat is likely the key reason for their absences in these extreme sections of the drainage.
These conditions consist of a very low or non-existent current resulting in low diversity and
abundance of mussels which the female turtle feed upon (Godwin pers. comm.).
All age classes of both species were seen throughout the study suggesting that they have been
in the system for at least two generations (≥ 28 years). However, the continuous range of G.
barbouri from south of I-10 in the Choctawhatchee River in Florida to the northern-most section
of the outer hybrid zone in the Pea River, suggests that there are many generations present. The
known range of G. barbouri in the Choctawhatchee River was compared with those in the
Ochlockonee and Wacissa rivers to find similarities that would suggest a human-introduced
population. There were almost no similarities, besides being recent discoveries, since the
populations in those river systems are known only from very few animals (three captures and
four observations in the Ochlockonee River; Wallace and Enge 2008, over two 162.0 km (100.7
mile) trips and one gravid female from the Wacissa River; Jackson 2003). It is worth noting that
one capture location in the Ochlockonee River was near a frequently used boat ramp and the
other was very remote. Enge believes that this population could possibly be natural (Enge pers.
comm.). Jackson’s captured nesting female G.barbouri from the Wacissa River oviposited 12
fertile eggs (Jackson 2003). This shows that there could have been some successful nesting on
the Wacissa River nearly 40 km east of the Ochlockonee River and near 80 km east of the
Apalachicola River. However, this is the only G. barbouri known from the Wacissa River.
51
G. ernsti has a much smaller range in the Choctawhatchee River system (Pea River) than G.
barbouri, but were seen with increased frequency as surveys and captures were made
sequentially upriver from the confluence. This frequency decreased as I approached within 10
km of the dam near Elba, AL. Graptemys sp outnumbered all other turtle species I observed and
captured during this study (Figure 6) in the Pea and Choctawhatchee rivers. The hypothesis (1)
that the Choctawhatchee River system populations of G.barbouri and G. ernsti were created by
releases by people is unlikely, at least in the last 30 years, due to their large and continuous range
in the system (as opposed to the Wacissa and Ochlockonee rivers) and comparable densities
within that range to densities in other drainages.
The second hypothesis (2) involves stream capture (Godwin 2002) of the Pea River by the
Choctawhatchee River. Stream capture, in this instance, involves the Pea River (then a tributary
of the Yellow River) shifting sharply to the east, probably from erosion, and being captured by
the Choctawhatchee River. This connection would allow fauna from the Choctawhatchee River
to disperse into the Pea River and vice-versa. This also assumes that the Pea River loses its
connection to the Yellow River at some point and gene flow between G. ernsti from the Yellow
and Pea rivers.
With this hypothesis, G. barbouri successfully colonized the lower Pea River and continues
to work its way upriver. G. barbouri is currently the dominant Graptemys species in the Pea
River, at least as far upriver as the US-87 bridge (west of the dip into Florida). As far as G.
ernsti, the current range suggests it to be unsuccessful at colonizing the Choctawhatchee River.
G. ernsti may have actually lost territory (perhaps from competition) in the extreme lower Pea
River, assuming that it occupied the entire lower river at the time of the stream capture event.
52
Comparisons of general river corridor direction were made of adjacent river drainages to the
Pea River. The Conecuh, Yellow, and Apalachicola all follow a mostly northeast to southwest
direction. However, the Pea River shows a strong northwest to southeast path, especially in the
lower section of the river (Figure 34). This sharp eastern turn of the river corridor suggests an
environmental event that led to the capture by the Choctawhatchee River. Therefore, because of
the sharp northwest to southeast turn of the lower Pea River that eventually connects to the
Choctawhatchee River, the dominance of G.ernsti in the upriver sections of the Pea River south
of the dam in Elba, AL, and the close proximity of the Yellow River to the Pea River (where G.
ernsti is the dominant Graptemys species), stream capture is the most likely hypothesis (2) that
enabled G.barbouri to enter the Pea River.
Species that are found in multiple, adjacent drainages can usually be traced back to a common
connection due to stream capture or a common bay. Distributions of other faunal groups both
defend the stream capture hypothesis and other groups are not consistent with it. Endemic
Choctawhatchee mussels such as Elliptio mcmichaeli (Mollusca; fluted elephantear) and
Fusconaia burkei (Mollusca; tapered pigtoe) are not known from the neighboring rivers (Yellow
and Chipola rivers) of the Choctawhatchee (Mirarchi et al. 2004). This provides some evidence
to negate the stream capture hypothesis because if the Choctawhatchee River captured the Pea
River, these endemics should have infiltrated the Yellow River system. However, these mussels
may have been unsuccessful in the Yellow River and naturally went extinct or these species
arose after the river capture event. However, Lampsilis australis (Mollusca; southern sandshell)
is endemic to the Conecuh/Escambia, Yellow, and Choctawhatchee rivers (Blalock-Herod et al.
2002) suggesting that there was a connection between the Choctawhatchee and Yellow rivers.
For example, G. ernsti is found in the Escambia River in Florida, as well as the Yellow River.
53
The two rivers are not connected, but they share the same bay (Escambia Bay). There are no
endemic fish in the Choctawhatchee River, suggesting that a connection with other drainages
was not too long ago, resulting in a lack of speciation and river endemism. The method by which
movement of freshwater fish from one river system to another during sea level fluctuation events
is how dispersal of Gulf Coast Graptemys is explained (Lovich and McCoy 1992), particularly
the pulchra-group. When sea levels fall, new river pathways and bays are formed that likely lead
to dispersal.
The third hypothesis (3), involving overland migration of turtles to adjacent drainages was
investigated by finding the closest path to neighboring river systems. Overland migration of G.
barbouri has only been reported once (Crenshaw and Rabb 1949) and is considered extremely
rare for these highly aquatic turtles (Sanderson 1974). However, it is not impossible that
extended high-water events, such as flooding from heavy rainfall or tropical storms, could allow
for dispersal of turtles to nearby water bodies or tributaries, especially if there is a brief
connection. Even if short overland migration is possible with these turtles, it certainly is not with
water-bound fauna, such as fish or mussels without a connection. Gulf Coast map turtles show
high fidelity to the river or stream channel, even during flood conditions (Lechowicz 2005) and
evidence of overland migratory behavior is lacking or unknown (Shealy 1976). Gravid female G.
ernsti were found as far as 150 meters (Shealy 1976) from the river, while searching for nesting
areas. Males have not been reported to wander around on land. Neonates can get disorientated
after hatching and can end up short distances from the river (Humbert pers. comm.).
With G. barbouri, migration to the Choctawhatchee River drainage is most likely from the
Chipola or Chattahoochee rivers (Table 21). Omusee Creek (Chipola) is 3.67 km from Little
Choctawhatchee River (Choctawhatchee). The same distance of 3.67 km is between Big Creek
54
(Chipola) and Wrights Creek (Choctawhatchee). Between Big Creek (Chipola) and Holmes
Creek (Choctawhatchee) is a distance of 3.63 km, which is the closest distance between the two
drainages. Dry Creek (Chipola) is 4.95 km from Hard Labor Creek (Choctawhatchee). As far as
G. ernsti, Big Creek (a tributary of the Choctawhatchee River) is 16.25 km from the Conecuh
River. Flat Creek (Choctawhatchee) is 13.5 km from Lightwood Knot Creek (Yellow River;
Table 21). The fact that overland migration is unknown in both species and the large distances
recorded between these drainages mostly rules out overland migrations as a method of dispersal.
However, this is based upon current maps of the drainage and not on the distances between
drainages in the past (during sea level fluctuations).
Discussion
Since none of the three hypotheses can be proven with the available evidence, my conclusions
are a result of choosing the most realistic scenario. The accidental or purposeful human
introduction and establishment of both species (1) is highly unlikely due to their large range in
the drainage, all age classes being seen throughout and a generation time of 14 years. It would
take a dedicated effort to successfully introduce two species and have both succeed in the river
system. Plus, this would require a quite a few turtles to be released in subsequent years. An
historical, commercial need is not known for these turtles that would provide motivation to do
this. Not until the last 25 years has there been any notable pressure from the national and
international pet trade. Neither species was in high demand like bog turtles (G. muhlenbergii;
Klemens 2001) and wood turtles (G. insculpta; Harding 2004) in recent decades, even before
they were completely protected in Alabama, Georgia and Florida. However, there was some
pressure from the pet trade which caused the Genus Graptemys to be added to CITES in 2006
(Ernst and Lovich 2009) and to impose non-commercial possession limits in Florida (Bill Turner
55
pers. comm.). With Florida’s legislation change in 2009, these two species were totally protected
from collection throughout their range.
The second hypothesis (2) is the most realistic and plausible of the three theories that
explain the presence of G. ernsti in the Pea River. This hypothesis states that a branch of the
Yellow River (that would later be called the Pea River) was captured by the Choctawhatchee
River (Godwin 2002). This also assumes that G. barbouri was already occupying the
Choctawhatchee River at the time of capture. This would have allowed G. barbouri to enter the
Pea River and begin to expand its range upriver while incidentally creating hybrids of these two
closely related species. If this is the case, why didn’t G. ernsti infiltrate enter the
Choctawhatchee River downriver after the stream capture? The habitat downriver of the
confluence with the Choctawhatchee River is ideal map turtle habitat with many curves in the
river providing ample deadwood basking material and sandbars on which to nest. Also, some of
my highest basking numbers are from this section as you continue into Florida.
I believe there are two possible scenarios explaining why G. ernsti did not expand its range
into the Choctawhatchee River, while G. barbouri did infiltrate the Pea River after the river was
captured. First, G. barbouri is quite abundant around the confluence of the Pea and
Choctawhatchee rivers. This is evident from the basking surveys by Wallace (Enge et al. 2008)
and during this project near the Alabama-Florida border. G. ernsti may not have been very
common in the extreme lower Pea River near the confluence at the time of stream capture, as
shown during the time period of this project. After the Pea River was captured, G. barbouri may
have had little competition with G. ernsti in the southernmost stretch of the Pea River. G.
barbouri may have just claimed a mostly unused territory in that section of the Pea River due to
56
the lack of competition. It is likely that the rate of range expansion up the Pea River by G.
barbouri lessened as it intersected with denser populations of G. ernsti.
Second, G. barbouri may be the dominant Graptemys species in the drainage. These two
species occupy very similar niches in their respective parent drainages (Escambia/Conecuh River
(G. ernsti), Yellow River (G. ernsti), and Apalachicola River (G. barbouri). They are both the
only Graptemys to exist in these parent drainages, unlike river systems to the west that contain
sympatric populations of a microcephalic and megacephalic map turtle species. These rivers with
allopatric Graptemys species contain a single megacephalic map turtle species in which the
females feed exclusively on hard-shelled prey (mollusks, snails, etc). Resource competition
studies (food partitioning) have not been conducted with these two species in the
Choctawhatchee River, as of yet. Since this is the only known occurrence of Gulf Coast
megacephalic sympatric species, nothing is known about how these niche-sharing species
coexist. There is a possibility that G. barbouri may be a more aggressive feeder or may be more
selective to higher nutrient prey than G. ernsti.
Another possibility is that G. barbouri may be a more dominant basker than G. ernsti. This
would lead to G. barbouri, particularly females, using the best basking logs to sun themselves
and could prevent G. ernsti from climbing out of the water (because they are in the way). G.
ernsti may be less apt to bask when G. barbouri is present, or wait longer in the water for an
available basking site. As with studies on less frequent basking due to high traffic rivers
(recreational tubing, canoeing, etc.; Pitt and Nickerson 2012), turtles do not gather the
appropriate amount of solar energy to produce as many eggs because they are always leaving
their basking logs.
57
Godwins (2002) stream capture hypothesis explains the origin of G. ernsti in the Pea River, as
well as the infiltration of G. barbouri up the Pea River. The origin of G. barbouri in the
Choctawhatchee River may have also been by stream capture of the Choctawhatchee River by
tributaries of the Chattahoochee River (Godwin 2002) in Alabama. However, the suspected
movement of Graptemys species during Pliocene and Pleistocene sea level fluctuations (Lovich
and McCoy 1992) may have allowed G. barbouri to enter the Choctawhatchee from the Chipola
River in Florida. The current abundances from basking surveys and captures shows that G.
barbouri is more abundant south of the Alabama border in the Choctawhatchee River than above
its confluence with the Pea River in Alabama.
The third hypothesis (3) involves turtles moving across land during flood events. Possible
examples include G.barbouri entering a creek or stream of the Choctawhatchee River system
from an outer tributary of the Chattahoochee River or Chipola rivers. Another example would be
G.ernsti entering a western tributary of the Pea River from a far eastern tributary of the Yellow
River during extreme flooding events.
Although Graptemys rarely travel over land (Jackson 1975, McKown 1972), range expansion
by this method is not impossible, if the distance is short enough or there is a brief connection. As
far as G. barbouri, distances of 3.63 – 4.67 km were found, at three locations, between tributaries
of the Chipola River and Choctawhatchee River. Also, a distance of 3.67 km was discovered
between outer streams of the Chattahoochee River and the Choctawhatchee River. However,
with G. ernsti, the distances between the Pea River and a tributary of the Yellow River (13.5 km)
and the Conecuh River (16.25 km) were much farther than with G. barbouri and less plausible.
58
The basis for this theory is that during high water, due to excessive rainfall and flooding,
turtles will leave their drainage and migrate to an adjacent drainage. Graptemys are not known to
be colonizing turtles (outside of their drainage) without a connection. Extreme flooding is
common in the Florida panhandle and south Alabama, so opportunities for possible range
expansion are somewhat conceivable. During extreme conditions, the river corridor can be
mostly indiscernible and the farthest tributaries can resemble flooded woodlands. If Graptemys
occur at the extremities of these far-reaching tributaries, a 3-4 km trek (as predicted with G.
barbouri) to the next drainage, without an aquatic connection, may not be impossible but highly
unlikely during extreme flood events. It is also unlikely that both species would leave and
successfully reach the adjacent drainage and establish new populations. If the habitat in these
farthest branches of the river were unsuitable, it is more likely that turtles would travel toward
the main river channel instead of venturing overland. It is even less likely that G. ernsti could
successfully venture 13.5 km or more to penetrate the adjacent drainage (Choctawhatchee River
drainage). However, it is unknown how close these tributaries would have been from each other
at the period of suspected migration.
Future Research
Future studies in the river system should include food partitioning because of the possible
competition between female G. barbouri, G. ernsti. It is possible that these Graptemys species
(female) are targeting specific food items (such as specific bivalve species or specific size
bivalves), independent of the other species. The apparent smaller range of G. ernsti might be due
to direct competition over food resources as well as basking sites due to G. barbouri a less shy
species. The presence of hybrids in the river system adds another layer of complexity to the
59
equation. This G. barbouri x G. ernsti may add a third layer of partitioning or just act as a
generalist of the required food source.
There are other Gulf Coast river systems between Texas and Florida where Graptemys
species are not known. It is not impossible that yet another instance of an undiscovered turtle
may be found some day. Many of the river systems, without Graptemys species, are blackwater
rivers. These rivers are rich with decomposing vegetation and have a dark brown color (tannins).
As a result, these rivers generally lack megacephalic Graptemys species. However, at least one
microcephalic Graptemys species have been shown to exist in this habitat. The southern variety
of G.nigrinoda (G.n.delticola) exists in extreme southwestern Alabama in the convergence of
several rivers (Tensaw, Alabama, Tombigbee) before they empty out in the estuary and the Gulf
of Mexico. These converging rivers form countless webs of channels between them and flow
through hardwood and cypress forests that allow high densities of organic debris to enter the
rivers. As a result, most mollusks are unable to thrive in these sections of the river. This limits
the down river range of G. pulchra, the Alabama River drainage megacepahalic Graptemys
species but not G. nigrinoda (the sympatric, microcephalic species in that drainage). Due to the
higher number of blackwater rivers as compared to non-blackwater rivers, a new microcephalic
species or known microcephalic species in an adjacent drainage is more likely to be found.
Conclusions
Graptemys were unknown from the Choctawhatchee River drainage before 1996. The
discovery of two megacephalic species 1997 and 2001 in a Gulf Coast River drainage, where no
Graptemys species has been known before was unexpected. This study added to the very limited
knowledge that is known about Graptemys in the Choctawhatchee River system.
60
Basking Surveys
(1) Basking surveys showed that I found higher turtles per river kilometer, 9.54
Graptemys/rkm, than Godwin (0.93 Graptemys/rkm; 2002) and Wallace (5-7 Graptemys/rkm;
2008) on the Pea and Choctawhatchee rivers. (2) Also, average Graptemys per kilometer data at
my sites (9.54 Graptemys/rkm) in the Choctawhatchee and Pea rivers were comparable to that
from Chipola River (2.64 -13.67 G. barbouri/rkm; Moler 1986). This means that turtles were
seen at the same abundance or higher on the Choctawhatchee as were in a parent drainage. All
age classes of Graptemys turtles were seen during basking surveys. This suggests a large and
well established population that has been established for at least two generations, but
undoubtedly much longer than that. (3)Basking surveys showed that Graptemys were the
dominant basking turtles in two locations under ideal conditions, as opposed to P. concinna in a
previous study (Godwin 2002). I found that basking surveys, by themselves, are a poor method
of assessing turtle populations, because they are highly subjective to the person conducting them,
as well as the high number of submersed turtles that are not visible.
Range Determination
(4) By systematically trapping and catching turtles by starting at an area dominated by one
Graptemys species and ending at another area dominated by the other Graptemys species, I was
able to roughly estimate where the two species are sympatric and allopatric, as well as where the
highest possibility of hybridization can occur. (5) Several long sequential treks up the Pea and
Choctawhatchee rivers while counting and capturing turtles has enabled me to create a more
detailed range map as to the actual range of these turtles as of 2008. This area was named the
hybrid zone. The hybrid zone is separated into two sections, the inner hybrid zone where G.
61
barbouri and G. ernsti were collected at a near 1:1 ratio and the outer hybrid zone where both
species have been documented but not at a 1:1 ratio. The ranges of these two species are believed
to be dynamic and change over time, even year to year.
Extremes in river level from May- October, such as drought during this study causing high
predation of hatchlings and flooding in 2005 from Hurricane Katrina causing nest inundation,
can wipe out most of the hatchlings in a given year. However, many larger juveniles and adults
appear to be able to survive these events. Recruitment in 2008, after the drought of 2007, on the
Pea and Choctawhatchee rivers appeared to at near-normal levels, as well as subsequent trips to
affected Gulf Coast Graptemys rivers the year after Katrina. It is my belief that as long as these
extremes in river level are periodic and not annual, then populations are able to recuperate in
subsequent years.
Morphological Differentiation
During this study, I named hybrids as having ~1:1 ratio of G. barbouri and G. ernsti traits,
based on head, chin and carapacial markings. This method was used in order to account for
variation in the population that may not be due hybridization. Several other specimens showed a
lower ratio of morphological traits that were not referred to as hybrids, but may have been. These
questionable specimens were noted as so, and genetic samples were taken for future analysis.
(6) I found two similar morphological characteristics of hybrids pertaining to head patterns.
Hybrids had reduced postorbital blotches that many times resulted in opposite narrow lateral
branches or the blotches were reduced from the posterior center resulting in the outside posterior
edge resembling a posterior pointing arrow.
62
(7) Statistical analysis revealed that pigment width on the upper and lower 5th marginal scute
in G. barbouri and G.ernsti from the Choctawhatchee River drainage was significantly wider
(measuring at the midline) than those from the parent drainages (Escambia, Yellow,
Apalachicola rivers). Relative carapace height (RCH) and relative carapace width (RCW) in
juvenile G. barbouri and G. ernsti are greater than those from parent drainages, however, males
and females are about equal, with the exception of female G. barbouri in RCH which was
marginal. (8) There is no difference in RCH and RCW from juveniles, of both species, from the
hybrid zone as compared with those outside the hybrid zone in the Choctawhatchee River. The
RCH and RCW of hybrids are more similar to that of G. ernsti from the Choctawhatchee River
than G. barbouri.
(9) I was unable to locate a nesting female hybrid Graptemys in the Pea River, so I could
incubate and hatch them in a laboratory. If I had and they hatched successfully, this would have
shown me the phenotypes of hatchlings from a hybrid female. I hypothesized that not all
neonates would show evidence of hybridization and those would be indiscernible from pure
species by morphology alone. The implications of that would have meant that I likely captured a
lot more hybrids than I accounted for.
Biogeographical Considerations and the Potential Origin of these Turtles in the
Drainage
The three most likely hypotheses as to how these two species arrived in the Choctawhatchee
River drainage were human introduction, stream capture, and overland migration. (10) Evidence
from my thesis findings on turtle populations today are inconsistent with hypothesis 1 (human
releases) and inconclusive with hypothesis 3 (overland migration during high water events) for
63
how G. barbouri and G. ernsti arrived in the Choctawhatchee River system. (11) Hypothesis 2
(stream capture) is supported by the current range of G. ernsti in the drainage, as well as the
overall river direction as compared to neighboring rivers. As far as G. barbouri, stream capture
of Choctawhatchee tributaries by Chattahoochee tributaries and/or Chipola tributaries could have
resulted in this species entering the system. Distances between Chipola and Choctawhatchee
tributaries was less than 4 km, and an extreme flood may have caused a connection (especially at
an earlier period) allowing G. barbouri to enter the Choctawhatchee River system. However, sea
level decrease may have resulted in a connection of the Chipola to the Choctawhatchee River, as
suspected in the pulchra-group of Graptemys from the Alabama River to the Escambia, Yellow,
Pascagoula and Pearl drainages during the Pliocene and Pleistocene Epochs (Lovich and McCoy
1992).
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Mirarchi, R. E., J. T. Garner, M. F. Mettee and P. E. Neil. 2004. Alabama Wildlife Volume Two:
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Moll, E. O., and D. Moll. 2000. Conservation of river turtles. Pp. 126-155, in Turtle
Conservation (M. W. Klemens, editor). Smithsonian Press, Washington, D.C.
Mount, R. H. 1975. The reptiles and amphibians of Alabama. Auburn University Agricultural
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Pitt, A., M. Nickerson. 2012. Reassessment of the turtle community in the North Fork of White
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Tortoise Society Journal. 2 (1):2-25.
Sanderson, R. A. 1974. Sexual dimorphism in the Barbour's map turtle, Malaclemys barbouri
(Carr and Marchand). M.S. thesis, University of South Florida, Tampa.
Shealy, R.M. 1976. The natural history of the Alabama map turtle, Graptemys pulchra Baur, in
Alabama. Bulletin of the Florida State Museum Biological Sciences 21:47-111.
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68
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van Dijk, P.P. 2011. Graptemys barbouri. In: IUCN 2013. IUCN Red List of Threatened
Species. Version 2013.1
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Version 2013.1
69
Figures
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71
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73
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79
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82
83
84
85
86
Tables
Table 1. Turtle species observed during two basking surveys conducted at each of two sites, one on the
Choctawhatchee and one on the Pea River. Each survey transect covered 6 km of river (total = 24 km).
Turtle Species
GBa
GS
PC
PF
SM
20
0
14
2
4
12
7
3
62
Spring 2008-Pea River
0
19
18
1
9
2
2
5
56
Fall 2008-Choctawhatchee River
45
0
21
3
7
6
15
6
103
Fall 2008 – Pea River
0
38
16
2
6
4
7
9
82
65
57
69
8
26
24
31
23
303
Location
Spring 2008-Choctawhatchee River
Total
a
AS
TS
UN
Total
Turtle species were: GB = G. barbouri, GS = unidentifiable Graptemys species, PC = P. concinna, PF =P.
floridana, SM = S. minor, AS = A. spinifera, TS = T. scripta, UN = unknown).
87
Table 2. The average Graptemys observed per river kilometer (rkm) during basking surveys in the
Choctawhatchee, Peam and Chipola rivers.
Graptemys observed per river kilometer
Survey location
Chipola River (Moler 1986)
2.64 – 13.67
Choctawhatchee River (Wallace 2008)
5 -7
Choctawhatchee and Pea rivers (Godwin 2002)
0.93
Choctawhatchee and Pea rivers (Lechowicz 2008) a
9.54
a
Represents two 6 km stretches of each river only.
88
Table 3. Total captures of G. barbouri, G. ernsti, and G. barbouri x G. ernsti hybrids on the
Choctawhatchee and Pea rivers from 2007-2008.
River
Species
G. barbouri
Choctawhatchee River
Pea River
Total
40
32
72
G. ernsti
0
38
38
G. barbouri x G. ernsti (hybrid)
0
5
5
40
75
115
Total
89
Table 4. Size class of all captured G. barbouri, G. ernsti, and G. barbouri x G. ernsti in the Pea and
Choctawhatchee rivers.
Size Class
Species/River
Adult male
Adult female
Juvenile
Hatchling
Total
G. barbouri
Choctawhatchee River
0
2
2
36
40
Pea River
2
3
3
24
32
Choctawhatchee River
0
0
0
0
0
Pea River
6
6
5
21
38
Choctawhatchee River
0
0
0
0
0
Pea River
0
0
2
3
5
Total (both rivers)
8
11
12
84
115
G. ernsti
G. barbouri x G. ernsti
a
Size classes were: M =Adult male, F = Adult female, J = Juvenile (unsexable), H = hatchling (unsexable).
90
Table 5. Total observations (including captures) of G. barbouri, G. ernsti, and G. barbouri x G. ernsti
hybrids, unidentifiable Graptemys (from basking surveys), P. concinna, P. floridana, T. scripta, S. minor,
A. spinifera, and C. serpentina on the Choctawhatchee and Pea rivers from 2007-2008.
River
Species
G. barbouri
Choctawhatchee River
Pea River
Total
105
32
137
G. ernsti
0a
38
38
G. barbouri x G. ernsti (hybrid)
0a
5
5
Unidentifiable Graptemys
0
57
57
P. concinna
39
37
77
P. floridana
5
5
10
T. scripta
22
11
33
S. minor
14
19
33
A. spinifera
0
8
8
C. serpentina
0
1
1
Unidentifiable turtles
9
14
23
194
227
421
Total
a
Graptemys observed during basking surveys in the Choctawhatchee River were assumed to be pure G.
barbouri (n = 64). All captured Graptemys in the Choctawhatchee River were verified to be G. barbouri
(n = 41).
91
Table 6. Morphological characteristics of G. barbouri and G. ernsti that were recorded during this study
(Lovich & McCoy 1992).
Species
Characteristic
G. barbouri
G. ernsti
Transverse bar under the chin
yes
no
Three small blotches under the chin
no
yes
“Y-shaped” pattern separating inter/post orbital blotches
yes
no
Combined interorbital and postorbital blotches
yes
no
Separated interorbital and postorbital blotches
no
yes
Supraoccipital spots connected to paramedian stripes
no
yes
Nasal trident
no
yes
Broken or unbroken “U-shaped” pattern under the chin
yes
yes
“C-shape” pattern on the 3rd and 4th costal scutes
yes
yes
“C” or “L-shaped” pattern on the upper 5th and 6th marginals
yes
yes
Wide “L-shaped” pattern on the lower 5th and 6th marginals
yes
yes
92
Table 11. Pigment width of the upper 5th marginal scute in G. barbouri from the Choctawhatchee
River and the parent drainages (Apalachicola, Chipola, Flint and Chattahoochee rivers) using the MannWhitney U Test.
River drainage
Location
# of specimens (n)
Choctawhatchee River
72
Parent Drainages a
92
Mean
0.1111
0.0851
Std. Deviation
0.0492
0.0254
Std. error
0.0049
0.0023
Median
0.1000
0.0900
Minimum value
0.6000
0.0400
Maximum value
0.1000
0.0900
p-value
< 0.0001 (significant)
a
Apalachicola (FL), Chipola (FL), Flint (GA), Chattahoochee (GA) rivers.
93
Table 12. Pigment width of the lower 5th marginal scute in G. barbouri from the Choctawhatchee River
and the parent drainages (Apalachicola, Chipola, Flint and Chattahoochee rivers) using the MannWhitney U Test.
River drainage
Location
# of specimens (n)
Choctawhatchee River
72
Parent Drainages a
92
Mean
0.4714
0.6108
St. Deviation
0.1043
0.0926
Std. error
0.0123
0.9649
Median
0.4700
0.6150
Minimum value
0.2100
0.0400
Maximum value
0.7300
0.7700
p-value
< 0.0001 (significant)
a
Apalachicola (FL), Chipola (FL), Flint (GA), Chattahoochee (GA) rivers.
94
Table 13. Comparison of head pattern traits in G. ernsti from the Choctawhatchee River and the parent
drainages (Escambia/Conecuh and Yellow rivers).
River drainage
Parent Drainages a
Traits present
Pea River
Nasal trident
0.763 (n =38)
1.000 (n = 129)
Supraoccipital spots connected
0.868 (n = 38)
0.310 (n = 116)
Connection of the interorbital blotch
to the postorbital blotches
0.026 (n = 38)
0.085 (n = 118)
a
Escambia (FL), Conecuh (AL), and Yellow (AL, FL) rivers.
95
Table 14. Comparison of relative carapace height (RCH) in juvenile, male, and female G. barbouri from
the Choctawhatchee River and parent drainages (Apalachicola, Chipola, Flint and Chattahoochee rivers)
using the Mann-Whitney U Test.
River drainage
Parameter
Parent Drainages a
Choctawhatchee River
Juvenile
male
female
Juvenile
5
5
male
36
female
# of specimens (n)
64
2
38
Mean
0.5470
0.4353
0.4790
0.4685
0.3976
0.4175
Std deviation
0.0358
0.0526
0.0515
0.0205
0.0149
0.0235
Std error
0.0044
0.0372
0.0230
0.0091
0.0025
0.0038
Minimum
0.4872
0.3981
0.4091
0.4430
0.3684
0.3846
Maximum
0.7576
0.4725
0.5309
0.7576
0.4368
0.4727
Median
0.5526
0.4353
0.4726
0.4780
0.3961
0.4126
p-value is 0.0002 (significant) for juveniles, 0.1698 for males and 0.0118 (significant) for females.
a
Apalachicola (FL), Chipola (FL), Flint (GA), Chattahoochee (GA) rivers.
96
Table 15. Comparison of relative carapace width in juvenile, male, and female G. barbouri from the
Choctawhatchee River and parent drainages (Apalachicola, Chipola, Flint and Chattahoochee rivers)
using the Mann-Whitney U Test.
River drainage
Parameter
Juvenile
# of specimens (n)
Parent Drainages a
Choctawhatchee River
64
male
female
2
5
Juvenile
5
male
female
36
38
Mean
1.016
0.7900
0.8240
0.9010
0.777
0.7928
Std deviation
0.0340
0.0172
0.0548
0.0610
0.0307
0.1604
Std error
0.0042
0.1221
0.0245
0.2729
0.0049
0.0214
Minimum
0.9189
0.7778
0.7622
0.8190
0.7240
0.2870
Maximum
1.0830
0.8022
0.8889
0.9590
0.8530
1.790
Median
1.0250
0.7900
0.8288
0.9070
0.7720
0.7860
p-value is 0.0003 (significant) for juveniles, 0.3800 for males and 0.1306 for females
a
Apalachicola (FL), Chipola (FL), Flint (GA), Chattahoochee (GA) rivers.
97
Table 16. Comparison of relative carapace height in juvenile, male, and female G. ernsti from the
Choctawhatchee River and parent drainages (Escambia/Conecuh and Yellow rivers) using the MannWhitney U Test.
River drainage
Parameter
Juvenile
# of specimens (n)
Parent Drainages a
Choctawhatchee River
89
male
6
female
6
Juvenile
26
0.5321
male
27
0.4337
female
49
Mean
0.4882
0.4370
0.4460
Std deviation
0.0160
0.0120
0.0204
0.0224
0.0215
0.0246
Std error
0.0017
0.0049
0.0083
0.0044
0.0041
0.0035
Minimum
0.4440
0.4272
0.4163
0.4773
0.3970
0.4000
Maximum
0.5240
0.4526
0.4740
0.5833
0.4890
0.4950
Median
0.4890
0.4317
0.4473
0.5294
0.4300
0.4440
p-value is < 0.0001 (significant) for juveniles, 0.6239 for males and 0.8080 for females
a
Escambia (FL), Conecuh (FL), and Yellow (FL, GA) rivers.
98
0.4432
Table 17. Comparison of relative carapace width (RCW) in juvenile, male, and female G. ernsti from the
Choctawhatchee River and parent drainages (Escambia/Conecuh and Yellow rivers) using the MannWhitney U Test.
River drainage
Parameter
Juvenile
# of specimens (n)
Parent Drainages a
Choctawhatchee River
26
male
6
female
6
Juvenile
89
male
27
female
49
Mean
0.9859
0.7884
0.7720
0.9232
0.7749
0.7730
Std deviation
0.4845
0.0201
0.0314
0.0514
0.0347
0.0555
Std error
0.0095
0.0082
0.0128
0.0055
0.0076
0.0079
Minimum
0.8701
0.7573
0.7273
0.7911
0.6750
0.6851
Maximum
1.057
0.8172
0.8195
0.9974
0.8667
0.9016
Median
1.000
0.7869
0.7676
0.9400
0.7723
0.7644
p-value is < 0.0001 (significant) for juveniles, 0.2249 for males and 0.9247 for females.
a
Escambia (FL), Conecuh (FL), and Yellow (FL, GA) rivers.
99
Table 18. Comparison of relative carapace height (RCH) and relative carapace width (RCW) in juvenile G.
barbouri from the hybrid zone in the Pea River and non-hybrid zone in the Choctawhatchee River using
the Mann-Whitney U Test.
Zone
Parameter
Hybrid zone
RCH
# of specimens (n)
RCW
Non-hybrid zone a
RCH
(23)
RCW
(38)
Mean
0.5461
1.0100
0.5444
1.017
Std deviation
0.2496
0.0329
0.0233
0.0352
Std error
0.0052
0.0068
0.0037
0.0052
Minimum
0.5000
0.9194
0.4872
0.9189
Maximum
0.5938
1.0630
0.5789
1.0830
Median
0.5526
1.0000
0.5526
1.0250
p-value is 0.8929 for RCH and 0.4622 for RCW.
a
Choctawhatchee River only.
100
Table 19. Comparison of relative carapace height (RCH) and relative carapace width (RCH) in juvenile G.
ernsti from the hybrid zone and non-hybrid zone in the Pea River using the Mann-Whitney U Test.
Zone
Parameter
Hybrid zone a
RCH
# of specimens (n)
RCW
Non-hybrid zone a
RCH
(18)
RCW
(8)
Mean
0.5332
0.9873
0.5296
0.9751
Std deviation
0.0255
0.4912
0.0144
0.0435
Std error
0.0060
0.0102
0.0050
0.0154
Minimum
0.4773
0.8701
0.5116
0.9048
Maximum
0.5833
1.0570
0.5500
1.0250
Median
0.5340
1.0000
0.5272
p-value is 0.6563 for RCH and 0.3886 for RCW.
a
Pea River only.
101
0.9762
Table 20. Comparison of relative carapace height (RCH) and relative carapace width (RCH) in juvenile G.
barbouri and G. ernsti from outside the hybrid zone in the Pea and Choctawhatchee rivers with G.
barbouri x G. ernsti hybrids from the hybrid zone using the Mann-Whitney U Test.
River drainage
Parameter
G. barbouri
RCH
# of specimens (n)
G. barbouri x G. ernsti a
G. ernsti
RCW
RCH
(65)
RCW
RCH
(26)
RCW
(7)
Mean
0.5470
1.016
0.5321
0.9859
0.5253
0.9485
Std deviation
0.0356
0.3414
0.0224
0.0485
0.0210
0.0593
Std error
0.0044
0.0042
0.0044
0.0095
0.0079
0.0224
Minimum
0.4872
0.9189
0.4733
0.8701
0.5055
0.8571
Maximum
0.7576
1.0830
0.5833
1.0570
0.5660
1.0260
Median
0.5526
1.0250
0.5294
1.0000
0.5156
0.9474
p-value
0.0591
0.0018
0.3321
0.1168
-
-
102
Table 21. Closest distances for overland migration of G. barbouri and G. ernsti from parent drainages to
the Choctawhatchee River system.
Choctawhatchee Waterway
River/creek
a
LC
WC
HC
HL
BA
FC
G. barbouri
Omusee Creek (Chattahoochee)
Big Creek (Chipola)
3.67
3.67
Big Creek (Chipola)
3.63
Dry Creek (Chipola)
4.95
G.ernsti
Conecuh River
16.25
Lightwood knot Creek (Yellow)
13.5
* Distances in km.
a
Choctawhatchee waterway were: LC = Little Choctawhatchee River, WC = Wrights Creek, HC = Holmes
Creek, HL = Hard Labor Creek, BA = Big Creek (Choctawhatchee), FC = Flat Creek.
103
Graphs
104
105
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