HISTORICAL DIET ANALYSIS OF LOGGERHEAD (CARETTA CARETTA) AND
KEMP’S RIDLEY (LEPIDOCHELYS KEMPI) SEA TURTLES IN VIRGINIA
____________
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---
A Thesis
Presented to
The Faculty of the School of Marine Science
The College of William and Mary in Virginia
In Partial Fulfillment
Of the Requirements for the Degree of
Master of Science- - - ---
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-------____________
by
Erin E. Seney
2003
For my parents, Becky and Frank, for their love and encouragement over the years,
and for my cat, Cuervo, who tolerated me when I smelled like turtle guts.
ii
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS..................................................................................................v
LIST OF TABLES.................................................................................................................vi
LIST OF FIGURES...............................................................................................................viii
ABSTRACT...........................................................................................................................xii
INTRODUCTION...............................................................................................................2
METHODS.........................................................................................................................14
Sample Collection..........................................................................................................14
Data Collection..........................................................................................................17
Data Analysis.............................................................................................................18
Diet descriptions.......................................................................................18
Diet comparisons......................................................................................20
RESULTS............................................................................................................................22
Loggerheads..................................................................................................................22
Interannual diet........................................................................................37
Size-specific diet.......................................................................................60
Sex-specific diet........................................................................................68
Interseasonal diet.....................................................................................68
Kemp’s Ridleys........................................................................................................73
Interannual diet........................................................................................87
Interspecific Competition............................................................................................93
DISCUSSION................................................................................................................103
Loggerheads..........................................................................................................103
Interannual diet......................................................................................103
Size-specific diet.....................................................................................106
Sex-specific diet.....................................................................................106
Interseasonal diet...................................................................................107
Kemp’s Ridleys......................................................................................................107
Interspecific Competition.........................................................................................108
iii
Page
Concluding Remarks.....................................................................................................108
APPENDICES.................................................................................................................110
LITERATURE CITED.........................................................................................................115
PREY IDENTIFICATION REFERENCES.......................................................................122
VITA................................................................................................................................123
iv
ACKNOWLEDGEMENTS
I would like to thank my major advisor, Dr. John (Jack) Musick, for his support
and guidance throughout this project. I am also grateful to my committee members, Drs.
John Brubaker, Robert George, and Roger Mann, for their time and advice. Although he
was not on my committee, Dr. David Evans provided much needed advice on data
analysis and reviewed a draft of this thesis. Dr. John E. Graves served as moderator for
both my qualifying exam and my defense.
This study would not have been possible without the efforts made by many
individuals throughout the VIMS Sea Turtle Program’s existence. As such, I would like
to recognize and thank every VIMS student, employee, and volunteer, as well as the
many state cooperators, who contributed to the collection of sea turtle gut samples and
stranding data from 1980 to 2002. Roy Pemberton showed me the VIMS sampling
protocol, and Meredith Fagan, Katy Frisch, Amber Knowles, and Anne Morrison helped
me considerably with sample collection, sieving, and preservation during the 2001 and
2002 stranding seasons. I am also thankful to Trish Bargo, Lisa McFarland, Wendy
Walton, and the other employees and volunteers from the Virginia Marine Science
Museum Stranding Team who collected samples during 2001 and 2002. My officemate,
Kate Mansfield, has taught me much about sea turtles, fieldwork, and the inner-workings
of a turtle program, as well as being a willing proofreader and great friend.
Jim Gartland provided valuable insight and assistance during all steps of my
project, from the literature search to prospectus edits to data analysis. Julia Ellis assisted
with many prey identifications and questions, as well as editing a thesis draft. Melanie
Harbin of the VIMS Fish Collection helped with fish identification, answered many
questions, and assisted me whenever I needed more preservation supplies. Ken
Goldman, Chris Hager, Juli Harding, Beth Hinchey, Mike Vecchione, and John Walter
also aided in various prey identifications. Bobby Harris helped me develop a Microsoft
Access database to link my data to the existing turtle database.
Joey Brown, Marilyn Lewis, Charles McFadden, and Diane Walker of the VIMS
Library provided assistance finding reference materials at VIMS, with interlibrary loans,
and in my search for horseshoe crab data. I am also grateful for the valuable reprints and
correspondence provided by Mike Frick (Caretta Research Project, Georgia), Rom
Lipcius (VIMS), Pamela Plotkin (East Tennessee State University), Carl Shuster (VIMS
emeritus), and Dale Youngkin (formerly Florida Atlantic University). Stephanie Iverson,
Rob O’Reilly, and Todd Watkins of the Virginia Marine Resources Commission
answered countless questions and provided landings data.
Lastly, I would like to thank my parents, Frank Seney and Becky Mazzarella; my
sisters, Lauren and Megan; my brother, Kevin; and my grandparents for their support of
my academic and scientific endeavors over the years.
v
LIST OF TABLES
Table
Page
1. National Marine Fisheries Service condition codes for stranded sea turtles.......................16
2. Virginia Institute of Marine Science condition codes for stranded sea turtles......................16
3. Composition of loggerhead diet data and samples collected during 1980 to
2002.............................................................................................................................27
4. Percent occurrence of all prey items found in loggerhead samples from
Virginia during 1983 to 2002 (n = 166).............................................................................45
5. Percent occurrence, percent dry weight, percent number, and percent index
of relative importance of all prey items found in whole loggerhead gut
samples from Virginia during 1983 to 1987 (n = 13)..........................................................47
6. Percent occurrence, percent dry weight, percent number, and percent index
of relative importance of all prey items found in whole loggerhead gut
samples from Virginia during 1988 to 1992 (n = 49).........................................................48
7. Percent occurrence, percent dry weight, percent number, and percent index
of relative importance of all prey items found in whole loggerhead gut
samples from Virginia during 1993 to 1997 (n = 20)........................................................50
8. Percent occurrence, percent dry weight, percent number, and percent index
of relative importance of all prey items found in whole loggerhead gut
samples from Virginia during 1998 to 2002 (n = 46).....................................................52
9. Prey species with five highest percent index of relative importance values
for loggerheads stranding in Virginia from 1983 to 2002 (n = 297)..................................56
10. Percent occurrence of all fish species found in loggerhead samples from
Virginia during 1983 to 2002 (n = 166)..........................................................................61
11. Composition of Kemp’s ridley diet data and samples collected during 1987
to 2002.....................................................................................................................81
12. Frequency of occurrence of all prey items found in Kemp's ridley
samples from Virginia during 1987 to 2002 (n = 33)......................................................95
vi
Table
Page
13. Percent occurrence, percent dry weight, percent number, and percent index
of relative importance of all prey items found in whole Kemp’s ridley gut
samples from Virginia during 1991 to 1994 (n = 5)...........................................................97
14. Percent occurrence, percent dry weight, percent number, and percent index
of relative importance of all prey items found in whole Kemp’s ridley gut
samples from Virginia during 2000 to 2002 (n = 18).........................................................98
vii
LIST OF FIGURES
Figure
Page
1. Annual reported horseshoe crab (Limulus polyphemus) landings for
(a) all of Virginia and (b) Chesapeake Bay, Virginia from 1980 to 2002............................8
2. Annual reported whelk landings for Virginia from 1992 to 2001...........................................9
3. Annual reported blue crab (Callinectes sapidus) landings for Virginia from
1980 to 2002................................................................................................................11
4. Approximate locations of all loggerheads (n = 179) and Kemp’s ridleys
(n = 33) from Virginia and Maryland from which samples were collected
during 1980 to 2002.......................................................................................................23
5. Approximate locations of all loggerheads from Virginia and Maryland from
which samples were collected during 1980 to 1989 (n = 60)............................................24
6. Approximate locations of all loggerheads from Virginia and Maryland from
which samples were collected during 1990 to 1997 (n = 70)..........................................25
7. Approximate locations of all loggerheads from Virginia and Maryland from
which samples were collected during 2000 to 2002 (n = 49)............................................26
8. Approximate locations of all loggerheads and Kemp’s ridleys from North
Carolina from which samples were collected during 1990 to 1992 (n = 8).......................28
9. Virginia sea turtle stranding regions.....................................................................................29
10. Annual distribution of (a) loggerhead samples (n = 185) and (b) loggerhead
diet data by state (n = 327, excluding 24 empties)...........................................................31
11. Annual distribution of loggerhead samples and data by data type (n = 351,
185 samples, 142 data only, 24 empty)..........................................................................32
12. Distribution of loggerhead samples by month and state (n = 185).................................33
13. Size distribution of (a) Virginia loggerhead whole samples (n = 128), (b) all
Virginia loggerhead samples (n = 169), and (c) all Virginia loggerheads with
diet data (n = 303).......................................................................................................34
14. Cumulative prey curve for whole loggerhead samples collected in Virginia
during 1983 to 2002 (n = 128).....................................................................................36
viii
Figure
Page
15. Linear regressions of loggerhead straight carapace length versus (a) total
dry weight of Virginia whole samples and (b) dry weights of large prey items
in Virginia whole samples collected during 1983 to 2002 (n = 128)..................................38
16. Linear regressions of loggerhead straight carapace length versus (a) total
number of prey items in Virginia whole samples and (b) total number of
large prey items in Virginia whole samples (n = 128)..........................................................39
17. Cumulative prey curves for whole loggerhead samples collected in Virginia
during (a) 1983 to 1987 (n = 13), (b) 1988 to 1992 (n = 49), (c) 1993 to 1997
(n = 20), and (d) 1998 to 2002 (n = 46)........................................................................40
18. Frequency of occurrence of (a) major prey groups in all loggerhead diet data
(n = 297) and (b) major prey items in all loggerhead samples (n = 166) collected
in Virginia during 1983 to 2002, grouped by five-year intervals........................................42
19. Biplots of year division and prey type principal components for PC1 and PC2
of a correspondence analysis using (a) %F values of all four general diet
categories and (b) %F values of three general diet categories from all Virginia
loggerhead diet data collected during 1983 to 2002 (n = 297).........................................43
20. (a) Frequency of occurrence, (b) percent dry weight, (c) percent number, and
(d) percent index of relative importance (IRI) in whole loggerhead gut samples
collected in Virginia from 1983 to 2002 (n = 128), grouped by five-year
intervals..........................................................................................................................54
21. Biplot of year division and prey type principal components for PC1 and PC2
of a correspondence analysis using %F values for major prey items from all
loggerhead samples collected in Virginia during 1983 to 2002 (n = 166).........................57
22. Biplots of year division and prey type principal components for PC1 and PC2
of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia
during 1983 to 2002 (n = 128)........................................................................................58
23. Cumulative prey curves for whole samples from Virginia loggerheads with
straight carapace lengths of (a) 40.0 to 49.9 cm (n = 13), (b) 50.0 to 59.9 cm
(n = 44), (c) 60.0 to 69.9 cm (n = 48), (d) 70.0 to 79.9 cm (n = 9), (e) 80.0 to
89.9 cm (n = 8), and (f) 90.0 to 99.9 cm (n = 6)...........................................................62
24. (a) Frequency of occurrence and (b) percent index of relative importance (IRI)
in whole loggerhead gut samples collected in Virginia during 1983 to 2002
(n = 128), grouped by ten-centimeter size classes (SCL)................................................65
ix
Figure
Page
25. Biplots of size class and prey type principal components for PC1 and PC2
of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia
during 1983 to 2002 (n = 128)........................................................................................66
26. Cumulative prey curves for whole loggerhead samples from Virginia taken
from (a) females (n = 73), (b) males (n = 26), and (c) unknowns (n = 29).......................69
27. (a) Frequency of occurrence and (b) percent index of relative importance (IRI)
in whole loggerhead gut samples collected in Virginia during 1983 to 2002
(n = 128), grouped by sex of turtle..................................................................................70
28. Biplots of turtle sex and prey type principal components for PC1 and PC2
of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia
during 1983 to 2002 (n = 128)........................................................................................71
29. Cumulative prey curves for whole loggerhead samples from Virginia during
(a) Spring (March to May, n = 47), (b) Summer (June to August, n = 64), and
(c) Fall (September to November, n = 14)......................................................................74
30. (a) Frequency of occurrence and (b) percent index of relative importance (IRI)
in whole loggerhead gut samples collected in Virginia during 1983 to 2002
(n = 128), grouped by season.......................................................................................75
31. Biplots of season and prey type principal components for PC1 and PC2
of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia
during 1983 to 2002 (n = 125, spring, summer, and fall only)...........................................76
32. Approximate locations of all Kemp’s ridleys from Virginia from which
samples were collected during 1987 to 1989 (n = 6).......................................................78
33. Approximate locations of all Kemp’s ridleys from Virginia from which
samples were collected during 1990 to 1994 (n = 9).......................................................79
34. Approximate locations of all Kemp’s ridleys from Virginia from which
samples were collected during 2000 to 2002 (n = 18)...................................................80
35. Annual distribution of (a) Kemp’s ridley samples (n = 35) and (b) Kemp’s
ridley diet data by state (n = 62, excluding 4 empties)......................................................82
x
Figure
Page
36. Annual distribution of Kemp’s ridley samples and data by data type (n = 66,
35 samples, 27 data only, 4 empty)..................................................................................84
37. Distribution of Kemp’s ridley samples by month and state (n = 35)................................85
38. Size distribution of (a) Virginia Kemp’s ridley whole samples (n = 23), (b) all
Virginia Kemp’s ridley samples (n = 33), and (c) all Virginia Kemp’s ridleys
with diet data (n = 59).....................................................................................................86
39. Cumulative prey curve for whole Kemp’s ridley samples collected in Virginia
during 1991 to 1994 and 2000 to 2002 (n = 23)............................................................88
40. Linear regressions of Kemp’s ridley straight carapace length versus (a) total
dry weight of Virginia whole samples and (b) dry weights of large prey items
in Virginia whole samples (n = 23)..................................................................................89
41. Linear regressions of Kemp’s ridley straight carapace length versus (a) total
number of prey items in Virginia whole samples and (b) total number of large
prey items in Virginia whole samples (n = 23)...............................................................90
42. Cumulative prey curves for whole Kemp’s ridley samples collected in Virginia
during (a) 1991 to 1994 2002 (n = 5) and (b) 2000 to 2002 (n = 18)...........................91
43. Frequency of occurrence of (a) major prey groups in all Kemp’s ridley diet
data (n = 59) and (b) major prey items in all Kemp’s ridley samples (n = 33)
collected in Virginia during 1983 to 2002........................................................................92
44. Biplots of year division and prey type principal components for PC1 and PC2
of a correspondence analysis using (a) %F values of general diet categories for
all Kemp’s ridley data (n = 59) and (b) %F values of major prey items from all
Kemp’s ridley samples (n = 33) collected in Virginia during 1983 to 2002....................94
45. (a) Frequency of occurrence, (b) percent dry weight, (c) percent number, and
(d) percent index of relative importance (IRI) in whole Kemp’s ridley gut
samples collected in Virginia from 1991 to 1994 and 2000 to 2002 (n = 23)..............100
xi
ABSTRACT
The Chesapeake Bay and coastal waters of Virginia, U.S.A. serve as foraging
grounds for loggerhead (Caretta caretta) and Kemp’s ridley (Lepidochelys kempi) sea
turtles from approximately May to October each year. Both loggerheads and Kemp’s
ridleys are known to feed primarily on benthic invertebrates as juveniles and adults, but
specific prey preferences vary between geographic regions. The Virginia Institute of
Marine Science Sea Turtle Program has collected diet data and gut samples from stranded
and incidentally caught sea turtles in Virginia since 1979. Examination of turtles that
stranded in Virginia during the late 1970s and early 1980s indicated that loggerheads fed
primarily on Atlantic horseshoe crab (Limulus polyphemus) and Kemp’s ridleys primarily
on blue crab (Callinectes sapidus).
During 1980 to 1994, 1997, and 2000 to 2002, 128 whole digestive tract samples
and 41 partial gut samples were collected from loggerheads in Virginia. Diet information
was noted on stranding datasheets for an additional 134 loggerheads from 1980 to 2002.
Twenty-three whole samples and 10 partial samples were collected in Virginia from
Kemp’s ridleys during 1987 to 1994 and 2000 to 2002, and data were available on an
additional 26 ridleys from 1983 to 2002. Prey items in the samples were identified to the
lowest possible taxonomic level, and dry weights and prey item counts were recorded.
Results indicate a shift in loggerhead diet from predominantly horseshoe crab during the
early to mid-1980s to predominantly blue crab during the late 1980s and early 1990s.
Loggerhead diet in the mid-1990s and 2000 to 2002 was dominated by finfish,
particularly menhaden (Brevoortia tyrannus) and croaker (Micropogonias undulatus).
These diet shifts suggest that fishery-related declines in horseshoe crab and blue crab
populations have caused loggerheads to instead forage on fish caught in nets or on
discarded bycatch. A slight seasonal effect on diet was also detected, and the diet of
juvenile loggerheads differed somewhat from that of the adults. The small Kemp’s ridley
dataset suggests that blue crabs and spider crabs (Libinia spp.) were important
components of ridley diet in Virginia during 1987 to 2002.
xii
HISTORICAL DIET ANALYSIS OF LOGGERHEAD (CARETTA CARETTA) AND
KEMP’S RIDLEY (LEPIDOCHELYS KEMPI) SEA TURTLES IN VIRGINIA
INTRODUCTION
Six species of sea turtles are found in the waters of the United States, and five of
these are found along the Atlantic and Gulf coasts. The loggerhead, Caretta caretta, and
the Kemp’s ridley, Lepidochelys kempi, are the most abundant species within the United
States and in Virginia (Keinath et al. 1987; USFWS 1998). The loggerhead sea turtle is
classified as “Threatened” under the U.S. Endangered Species Act of 1973, while the
Kemp’s ridley is listed as “Endangered” and is the least abundant sea turtle species in the
world (USFWS 1998).
Loggerheads are found circumglobally in tropical, subtropical, and temperate
waters, and they nest in temperate zones and in the subtropics. At least four genetically
distinct nesting populations are recognized and managed separately in the Northwestern
Atlantic (TEWG 2000). Two of the world’s largest loggerhead rookeries are found on
the Atlantic beaches of central and southern Florida, and other nesting grounds occur
along the U.S. coast from Virginia to Louisiana (NRC 1990). A petition was filed in
2002 to upgrade the Northern and Florida Panhandle subpopulations to “Endangered”
(NOAA 2002), and it is currently under evaluation by the National Marine Fisheries
Service. Mitochondrial DNA analysis indicates that about 36% of Virginia’s juvenile
loggerheads originate from nesting beaches in North Carolina, South Carolina, and
Georgia, and approximately 69% of Virginia’s loggerheads originate from the Northern
subpopulation as a whole (Virginia to Northeast Florida) (Norrgard and Graves 1996).
2
3
Kemp’s ridleys are restricted primarily to the Gulf of Mexico and Northwestern
Atlantic Ocean. Although they forage in large numbers in U.S. waters, the only
important nesting site for the Kemp’s ridley is found at and around the beaches of
Rancho Nuevo in Tamaulipas, Mexico (TEWG 2000). Juvenile ridleys encountered in
Virginia and along the rest of the U.S. east coast are able to return to these nesting sites as
adults (TEWG, 2000; VIMS mark-recapture data).
The Chesapeake Bay, Virginia serves as an important seasonal foraging ground
for an estimated 5,000 to 10,000 sea turtles each year (Bellmund et al. 1987; Musick
1988; Keinath et al. 1987). These turtles are predominantly benthic-stage juvenile
loggerheads and Kemp’s ridleys, and the numbers of loggerheads that enter the Bay are
estimated at roughly ten times those of the Kemp’s ridley (Musick 1988; Keinath et al.
1994). The Atlantic green turtle (Chelonia mydas) and Atlantic leatherback
(Dermochelys coriacea) also enter Virginia waters, but in substantially smaller numbers,
and there have only been two records of hawksbill sea turtles (Eretmochelys imbricata) in
Virginia since 1979 (Virginia stranding data). Sea turtles begin to enter Virginia’s
coastal waters and the Chesapeake Bay when water temperatures reach approximately 18
to 20o Celsius (Byles 1988; Coles 1999; Musick 1988), generally in mid- to late-May,
and they begin to migrate south in the fall once temperatures decrease (Coles 1999;
Mansfield et al. 2001).
The Virginia Institute of Marine Science (VIMS) Sea Turtle Program has served
as the Virginia center for sea turtle strandings, monitoring, and research since its
inception in 1979. Strandings are responded to by VIMS, the Virginia Marine Science
Museum (VMSM), and various state cooperators. Virginia’s strandings typically number
4
between 200 and 400 annually (Mansfield et al. 2002a), and most strandings occur
between mid-May and mid-October. A large stranding peak is usually seen in the late
spring or early summer as the turtles complete migrations to the Chesapeake Bay
(Mansfield et al. 2001). Data recorded on each stranded turtle include stranding location,
turtle measurements, decomposition state, noticeable abnormalities and wounds, and gut
contents. Tissue, bone, epibiota, and gut content samples are also collected, depending
on decomposition state of the turtle and research interests and requests.
Gut content analysis can aid in conservation and management decisions by
providing insight to the role of an organism in its environment. Diet composition studies
may also be employed to determine competition and habitat segregation between and
within sea turtle species (Burke et al. 1993; Keinath et al. 1987; Shaver 1991). The
presence of predominantly pelagic or benthic prey items can be used to determine the life
stages of stranded turtles (Van Nierop and Den Hartog 1984; Plotkin 1989; Plotkin 1996).
Immediately after hatching, both loggerhead and Kemp’s ridley sea turtles enter a
multi-year pelagic stage, during which the young turtles associate with Sargassum spp.
and feed on pelagic molluscs, crustaceans, and coelenterates, as well terrestrial insects
and anthropogenic debris (Bjorndal 1997; Bolten and Balazs 1995; Carr 1986; Musick
and Limpus 1997; Richardson 1991). More is known about the diet habits of these two
species after the pelagic stage, once the turtles have returned to coastal waters. Both
loggerhead and Kemp’s ridley sea turtles are known to be benthic carnivores as juveniles
and adults (Bjorndal 1985; Hendrickson 1980; Mortimer 1979), but their diets vary by
region.
5
The diets of the small juvenile loggerheads and Kemp’s ridleys that seasonally
forage off Long Island, New York have been evaluated using whole digestive tracts from
stranded animals and fecal samples from turtles caught incidentally in poundnets (Burke
et al. 1993; Burke et al. 1994; Morreale and Standora 1991). Crustaceans accounted for
the vast majority of prey items, and two slow-moving crabs, the nine-spined spider crab
(Libinia emarginata) and Atlantic rock crab (Cancer irroratus), were encountered most
frequently in samples from both species.
Reports from Georgia (Creech and Allman 1997; Frick 1997; Frick and Mason
1998) indicate that stranded Kemp’s ridleys from northern Georgia had consumed
“shallow water inhabitants” including blue crabs (Callinectes sapidus), mud snails
(Nassarius spp.), stone crabs (Menippe mercenaria), spider crabs (Libinia spp.), benthic
finfish, and Carolina diamondback terrapin (Malaclemys terrapin centrata) during the
mid-1990s. Stranded loggerheads collected during the mid- to late-1990s on Wassaw
Island and Cumberland Island, Georgia have contained predominantly spider and stone
crabs, as well as whelks (Busycon spp.), moon snails (Neverita spp.), and horseshoe crabs
(Limulus polyphemus) (Frick et al. 2001). In a long-term (1979 to 1999) diet study using
whole digestive tracts from loggerheads that stranded on Cumberland Island (n = 369),
Youngkin and Wyneken (in press) noted four diet shifts between crab and mollusc
dominance. Fish were found in approximately 50% of all samples, while horseshoe crabs
were only found in about 3%. Amounts of crab and fish varied significantly with curved
carapace length (CCL), with larger turtles eating proportionately more crabs and smaller
turtles eating proportionately more fish.
6
In Southern Texas, the diets of stranded loggerheads and Kemp’s ridleys have
been well documented. Plotkin et al. (1993) noted seventeen different prey groups in
samples from 82 stranded benthic-stage juvenile loggerheads. Sea pens, including
Virgualaria presbytes, were found in 56.1% of the turtles and accounted for 58.7% of the
total dry weight. Crabs occurred in 87.6% of the gut samples, but accounted for only
28.8% of the total dry weight. Walking crabs such as spider crabs, calico crabs (Hepatus
epheliticus), and purse crabs (Persephona mediterranea) seemed to be more important
than portunid crabs in the diet. Plotkin (1989, 1996) also identified some of the smaller
loggerheads stranding in Texas as pelagic-stage animals based on gut contents such as
Sargassum spp. and pelagic crustaceans and molluscs.
Shaver (1991) examined the gut contents of 50 wild and 51 head-started Kemp’s
ridleys, predominantly subadults (benthic-stage juveniles) that stranded in Southern
Texas. (Head-starting is a technique in which hatchlings are raised in captivity for at
least several months to reduce hatchling mortality (NRC 1990).) Crabs, including blue,
spider, and purse crabs, were most frequently observed and accounted for the greatest
proportion of the dry weight in both wild and head-started turtles. However, head-started
subadults consumed greater amounts of molluscs and fewer species of crabs than wild
subadults. The head-started turtles also consumed larger quantities of fish and shrimp,
probably in the form of bycatch.
In the first known publication referring to sea turtle diet in Virginia, Hardy (1962)
reported that crabs from the genus Callinectes accounted for approximately 95% of the
gut contents of a Kemp’s ridley found in Northumberland County. Later reports
(Bellmund et al. 1987; Lutcavage and Musick 1985; Musick et al. 1984) concluded that
7
loggerheads collected from 1979 to 1984 had consumed primarily horseshoe crabs, and
blue crabs, spider crabs, rock crabs, clam bodies, and fish were found in some digestive
tracts. During this same time period, Kemp’s ridleys examined had consumed mainly
blue crabs (Bellmund et al. 1987; Lutcavage and Musick 1985; Musick et al. 1984).
These prey preferences appear to correspond to the partitioning of habitat seen in
biotelemetric studies, with loggerheads feeding on horseshoe crabs in river mouths and
channels and Kemp’s ridleys foraging for blue crabs in shallower waters, including
seagrass beds (Byles 1988; Keinath et al. 1987; Lutcavage 1981; Musick et al. 1984).
Horseshoe crabs were once used in the U.S. for fertilizer and livestock feed, but
the commercial fishery has primarily caught horseshoe crabs for bait and biomedical uses
since the 1970s (Berkson and Shuster 1999; Botton and Ropes 1987). During the 1980s,
Virginia’s reported horseshoe crab landings averaged about 154,000 pounds per year, and
landings within the Virginia portion of the Chesapeake Bay peaked at about 80,000
pounds in 1986 (VMRC data 2003; Figure 1). A ban on all trawling in Virginia waters
was instated in 1989 (VMRC 1995), and Virginia horseshoe crab landings averaged only
about 21,000 pounds per year during 1990 to 1995 (VMRC data 2003; Figure 1a).
However, the Virginia whelk pot fishery took off from its inception in the early 1990s
(VMRC data 2003; Figure 2), and horseshoe crab became the bait of choice (Fisher 2000;
Mills 2000). Virginia’s commercial horseshoe crab landings, particularly from the ocean,
increased considerably during 1998 to 2000, peaking at nearly 1.9 million pounds in 1999
(Figure 1a).
8
FIGURE 1. Annual reported horseshoe crab (Limulus polyphemus) landings for (a)
all of Virginia and (b) Chesapeake Bay, Virginia from 1980 to 2002. Data courtesy
of Virginia Marine Resources Commission. Note: 2002 data is preliminary.
(a)
Millions of Pounds
2.0
1.5
1.0
0.5
Bay Tributaries (VA)
*2002
2000
1998
1996
1994
1992
1990
1988
Chesapeake Bay (VA)
1994
Ocean (VA)
1986
1986
1984
1982
1980
0.0
(b)
100,000
60,000
40,000
20,000
Chesapeake Bay (VA)
Bay Tributaries (VA)
*2002
2000
1998
1996
1992
1990
1988
1984
1982
0
1980
Pounds
80,000
9
FIGURE 2. Annual reported whelk landings for Virginia from 1992 to 2001. Data
courtesy of Virginia Marine Resources Commission. Note: mandatory reporting of
commercial whelk landings was enstated in 1993.
500,000
300,000
200,000
100,000
Channel Whelk
Knobbed Whelk
2001
2000
1999
1998
1997
1996
1995
1994
1993
0
1992
Pounds
400,000
10
Fishing pressure is believed to have reduced the observable horseshoe crab
population in the Northwestern Atlantic by 50% from 1990 to 1998, and drastic declines
have been seen in Delaware Bay (ASMFC 1998; Fisher 2000; Tanacredi 2001). In light
of the implementation of the Atlantic States Marine Fisheries Commission (ASMFC)
Horseshoe Crab Fishery Management Plan (1998) and apparent declines in Virginia
waters (Mills 2000), the Virginia Marine Resources Commission (VMRC) enacted a
number of regulations on the fishery starting in 2001. These included setting the state
horseshoe crab landing quota at 152,495 animals (approximately 400,000 pounds using
an average weight of 2.6 pounds) (ASMFC 1998; VMRC 2000). Just over 145,000
pounds were landed in 2001 (Figure 1a).
The level of fishing for the blue crab in the Chesapeake Bay has been considered
“intensive” since the early 1900s (Van Engel 1958). Virginia’s commercial landings
seldom exceeded 20 million pounds per year in the 1930s and 1940s, but they exceeded
32 million pounds per year in the late 1940s, and annual landings regularly exceeded 40
million pounds during 1965 to 1990 (Kirkley 1997). Average annual blue crab landings
dropped from about 41 million pounds during 1990 to 1995 to about 35 million pounds
during 1996 to 2001 (VMRC data 2003; Figure 3). Recent findings (Lipcius and
Stockhausen 2002) indicate that the Lower Chesapeake Bay blue crab spawning stock,
larval abundance, and postlarval recruitment were significantly lower in 1992 to 1999
than in 1985 to 1991. The decrease in all of these variables was rapid, occurring over one
to two years, indicating a phase shift rather than a progressive decrease. Poor recruitment
in 1991 in concert with high fishing and natural mortality are the proposed cause of the
diminished spawning stock in 1992. The blue crab stock, larval abundance, and
11
FIGURE 3. Annual reported blue crab (Callinectes sapidus) landings for Virginia
from 1980 to 2002. Data Courtesy of Virginia Marine Resources Commission.
Note: 2002 data is preliminary.
60
40
30
20
10
Ocean (VA)
Chesapeake Bay (VA)
Bay Tributaries (VA)
*2002
2000
1998
1996
1994
1992
1990
1988
1986
1984
1982
0
1980
Millions of Pounds
50
12
recruitment are not likely to rebound without significant reductions in fishing and natural
mortality, along with conditions conducive to successful recruitment (Lipcius and
Stockhausen 2002).
Further characterizing and quantifying the diet of loggerheads and Kemp’s ridleys
should provide insight to indirect and direct effects of Virginia’s fisheries on sea turtles.
The apparent declines in horseshoe crab and blue crab populations may have implications
for the diets of these turtle species, and the turtles could be forced to shift their diets to
other prey. In addition, it is believed that turtles are typically “not agile enough to
capture fish under natural conditions” (Bellmund, et al. 1987), and thus would only
consume large quantities of finfish by interacting with fishing gear (Bellmund et al. 1987)
or bycatch (Shoop and Ruckdeschel 1982). The presence of scavenging mud snails, such
as Nassarius spp. and Ilyanassa spp., along with fish in the gut may suggest that a turtle
has been feeding on dead, discarded bycatch (Plotkin et al. 1993; Shaver 1991).
Loggerhead and Kemp’s ridley gut content samples were collected by VIMS and
subsequently preserved and archived during 1980 to 1997. Six loggerhead samples from
1980 were quantified by Lutcavage (1981), but most of the samples collected afterwards
were examined in a cursory manner and saved for later analysis. The quantification of
the archived samples, with the addition of samples collected from 2000 through 2002,
represented one of the first long-term gut content analyses for both juvenile loggerheads
and Kemp’s ridleys. In addition to expanding on the limited knowledge of the diet of
these two species, this undertaking allowed for the examination of loggerhead and
Kemp’s ridley diet in Virginia over time as compared to temporal changes in prey
abundances. The objectives of this study were threefold:
13
1. To describe the diets of loggerhead and Kemp’s ridley sea turtles in Virginia
and help assess the role of sea turtles in the Chesapeake Bay food web.
2. To compare Virginia turtle diet over the time period of 1980 to 2002 and
between size classes, the sexes, seasons, and the two species.
3. To assess potential impacts of horseshoe crab and blue crab population
declines on loggerhead and Kemp’s ridley diets.
METHODS
Sample Collection
Opportunities for collecting sea turtle gut samples are somewhat limited because
these turtles are protected species. This contrasts to many studies conducted on finfish,
which can employ a variety of fishing gear to catch large numbers of fish per site
(Creaser and Perkins 1994; Hacunda 1981; Hynes 1950; Moore and Moore 1974). Shark
diet studies often have smaller sample sizes than finfish studies, and specimens are often
collected by hook and line (Stillwell and Kohler 1982) and longline sets (Gelsleichter et
al. 1999). Sample sizes tend to be even smaller in sea turtle diet studies, and gut contents
are often collected over a span of several years from strandings (Bellmund et al. 1987;
Burke et al. 1994; Plotkin et al. 1993; Shaver 1991) and as fecal samples (Burke et al.
1993). Gastric (esophageal) lavage can be performed on live turtles, but it is more
feasible for green turtles (Forbes 1999) and hawksbills (Mayor et al. 1998), which eat
primarily plant matter and sponges respectively.
The VIMS Sea Turtle Stranding Program and various stranding cooperatives
collected partial and whole digestive tract samples and fecal samples during 1980, 1983
to 1994, and 1997. These samples were stored in jars at VIMS in either 10% formalin or
70% ethanol. Those in 10% formalin were switched to 70% ethanol prior to data
collection. The portion of the digestive tract sampled was somewhat inconsistent prior to
1988, but most samples from later years were obtained from whole digestive tracts.
14
15
Additional samples, predominantly from whole digestive tracts, were collected from June
2000 to October 2002. The collection methods, sieve size, and preservation methods
used for the 2000 through 2002 samples were based on the techniques used to collect and
preserve the earlier samples (D. E. Barnard, pers. comm.; J. A. Keinath, pers. comm.; R.
A. Pemberton, pers. comm.), so that the samples would be comparable.
To obtain a whole gut content sample, the entire digestive tract, from the
beginning of the esophagus to the end of the large intestine, was dissected from a dead
stranded or incidentally caught loggerhead or Kemp’s ridley. These turtles were
primarily fresh dead (NMFS condition “1”, VIMS condition “3”; Tables 1 and 2) and
moderately decomposed (NMFS “2”, VIMS “3” and “4”), as well as some at the low end
of severely decomposed (NMFS “3”, VIMS “4”). After its removal, each digestive tract
was frozen, placed in 10% formalin, or immediately sieved. Each digestive tract was cut
open (after thawing or rinsing where appropriate), and the contents were emptied into a
500 µm brass sieve and rinsed thoroughly with water. The gut contents were placed in a
jar filled with 10% freshwater formalin and kept in formalin for at least 24 to 48 hours.
The formalin was then poured off, and each sample was allowed to soak in freshwater for
several hours before filling the jar with 70% ethanol. Stomach samples and other partial
gut samples were collected from some stranded animals, and fecal samples were
collected from some incidentally caught and live stranded turtles. These samples were
collected predominantly in the 1980s, and preservation procedures matched those used
for whole samples. Lavage was not attempted on live animals, due to low success of the
procedure on loggerheads (R. H. George, pers. comm.), the large and sharp nature of prey
items, the temperament of both species, and the size of most loggerheads in Virginia.
TABLE 1. National Marine Fisheries Service condition codes for stranded sea turtles.
Condition code
0
1
2
3
4
5
Description
Alive
Fresh dead
Moderately decomposed
Severely decomposed
Dried carcass
Skeleton, bones only
TABLE 2. Virginia Institute of Marine Science condition codes for stranded sea turtles.
Condition code
1
2
3
4
5
6
Description
Live, healthy
Live, sick
Dead, slight bloat
Dead, bloated, gray/green skin
Dead, bones showing, decomposed
Dead, bones only, scattered
17
The preservation procedure of 10% formalin followed by 75% ethanol is often
used to prepare scientific specimens for museums (Hangay and Dingley 1985), and 10%
formalin followed by 70% ethanol is currently standard for the VIMS Fish Collection (M.
Harbin, pers. comm.). Formalin is effective in hardening stomach contents (Creaser and
Perkins 1994) and preventing tissue decay (DiStefano et al. 1994); however, freshwater
formalin is also known to increase fish wet weights and decrease fish lengths (DiStefano
et al. 1994; Parker 1963). DiStefano et al. (1994) concluded that 10% formalin had no
significant effects on weights and measurements of a freshwater crustacean, the virile
crayfish (Orconectes virilis). Despite its potential effects on wet weights, the use of
formalin is considered acceptable if the methods are consistent throughout a diet study
(Hyslop 1980). Ethanol is also effective at preventing tissue decay in fishes and
crustaceans, and it lacks the potential serious risks to human health associated with
formalin (DiStefano et al. 1994).
Data Collection
Each gut sample was sorted into major groups such as crustaceans, fish, horseshoe
crabs, molluscs, and plants, and prey items were identified to the lowest possible
taxonomic level. All samples were kept after sorting to provide a reference collection of
prey items, and whole fish, scales, and skeletal preparations from the VIMS Fish
Collection were also used for reference. Numbers of prey items were determined when
possible, and wet weights were obtained to the nearest tenth of a gram. The samples
were dried at approximately 60o Celsius in a drying oven for 24 to 48 hours (Burke et al.
1994; Forbes 1999; Plotkin et al. 1993; Shaver 1991) and dry weights were taken to the
18
nearest tenth of a gram after cooling. Numerical counts were collected because they
provide information about feeding behavior, and weights because they can reflect dietary
nutritional values (Macdonald and Green 1983); however, the large amounts of
indigestible crab, fish, and mollusc parts present in whole sea turtle digestive tracts and
fecal samples may result in some bias (Burke et al. 1993; Plotkin et al. 1993).
All gut content data were linked to the original stranding data in a Microsoft
Access database. Additional diet information on turtles that were necropsied but not
sampled was compiled from the VIMS stranding database. All data entry was verified
prior to analysis.
Data Analysis
Diet descriptions
Cumulative prey curves were used to evaluate whether a sufficient number of
whole samples had been examined to adequately describe the diet of each species and
various temporal, size class, and sex subsets (Cortés 1997; Gelsleichter et al. 1999; Ferry
and Calliet 1996). These curves were constructed by randomizing the order in which
samples were analyzed ten times using Resampling Stats, Inc. Excel Add-in Version 2.0
(www.resample.com) and then plotting the mean cumulative number of prey types versus
the number of samples examined (Gartland 2002; Gelsleichter et al. 1999). The
minimum number of gut samples that are needed to obtain “precise” and “more reliable”
results occurs once the curve has reached its asymptote (Cortés 1997).
Percent occurrences (frequency, %F) of general prey groups (horseshoe crab,
crustaceans, molluscs, and fish) were determined for all diet data from Virginia, and
19
percent occurrences of specific prey items were determined for all Virginia samples and
whole samples. Percent dry weight (%W) and percent number (%N) were also calculated
for prey items in the whole samples, since multiple measures are often necessary when
prey items differ in size (Ferry and Calliet 1996). Wet weights were not analyzed
because of the large discrepancy between total sorting time for individual samples
(ranging from several minutes to several hours).
Compound indices that incorporate occurrence, bulk, and numbers appear to
provide a more accurate description of dietary importance, and they can facilitate
comparative studies (Cortés 1997). The index of relative importance (IRI) (Pinkas et al.
1971), a compound diet index used frequently in the fish literature, was calculated for
general prey groups and individual prey items in the whole loggerhead and Kemp’s ridley
gut samples from Virginia. The original index combined numeric, occurrence, and
volumetric data into one value (Pinkas et al. 1971), but the modification introduced by
Hacunda (1981) that incorporated weight instead of volume was used in this study:
IRIi = (%N i + %Wi) * %Fi
where IRIi is the index of relative importance value for prey type i. To promote
consistency and facilitate comparisons, IRI was also calculated for the whole samples on
a percentage basis (Cortés 1997):
%IRIi = 100 * IRIi / Σ IRIi
where Σ IRIi is the sum of the IRI values all prey categories.
Linear regressions were performed using Minitab Version 12.1 to determine if
there was any relationship between turtle size (straight carapace length) and dry weights
and numbers of prey items in whole samples from all Virginia loggerheads and Kemp’s
20
ridleys. Minitab performs an analysis of variance (ANOVA) in conjunction with each
linear regression to determine if the null hypothesis (Ho ) that the slope generated by the
regression is zero can be rejected. If this null hypothesis is rejected, the regression is
considered significant (Moore and McCabe 1998).
Diet comparisons
To increase sample sizes, the Virginia loggerhead data were grouped into fiveyear increments from 1983 to 2002. The data were also examined in ten-centimeter size
classes from 40 to 100 cm, by sex of turtle, and by season. Due to the limited amount of
Kemp’s ridley data, the year divisions of 1983-1984, 1987-1989, 1991-1994, 1999-2000,
and 2001-2002 were examined for the general diet information. Whole Kemp’s ridley
samples were only collected from 1991 to 1994 and 2000 to 2002, so these divisions were
used in whole sample analysis.
Correspondence analysis (CA) is a multivariate ordination technique similar to
principal component analysis (PCA), and it is considered appropriate for count data
presented in contingency tables (Davis 1989; Gartland 2002). The CA technique was
used to identify variations in Virginia loggerhead diet between the five-year groupings,
size classes, sexes, and seasons using %F, %W, %N, and %IRI values. Correspondence
analysis was also used to examine %F for all Kemp’s ridley data and samples during the
various year divisions. Diet variations between stranding regions were not examined
because dead turtles may float with winds, currents, and tides for days to weeks prior to
stranding on land (Mansfield et al. 2002a, 2002b).
21
The %F, %W, %N, and %IRI values for large, frequently occurring prey items
(horseshoe crab, all crab species, bony fish, Busycon whelks (Busycon spp.), and Atlantic
moon snail (Neverita duplicata)) were entered into worksheets in Minitab Version 12.1 to
run correspondence analyses. Each turtle grouping (years, sizes, sexes, seasons) was
examined separately for each data type (%F, %W, %N, %IRI) due to the small number of
whole samples in each of the divisions. All values were rounded to the nearest whole
integer, as required by Minitab to run a CA. The CA technique operates on a matrix
derived from a contingency table, and row (years, sizes, sexes, or seasons) and column
(prey type) principal components (PCs) are calculated using eigenanalysis (Davis 1986).
Biplots of the first and second PCs for both rows and columns were constructed for each
turtle grouping by data type to identify potential patterns in diet.
Diet overlap between the species and various subsets of loggerheads was
computed using the Schoener (1970) index:
α = 1 – 0.5(Σ |pxi – pyi|)
where pxi is the proportion of food category i in the diet of species x, and pyi is the
proportion of food category i in the diet of species y (Schoener 1970; Wallace 1981).
This index ranges from zero to one (no diet overlap to complete overlap) and can be
multiplied by 100 to yield percent overlap. A comparison of four diet overlap indices by
Wallace (1981) concluded the Schoener index is one of the “least objectionable” indices
available when resource availability data are absent. Additionally, Wallace concluded
that the average of individual volume percentages was a less objectionable measure than
percent occurrence in all guts, percent of total number of prey items in all guts, and
percent of total volume in all guts for evaluating diet overlap.
RESULTS
Loggerheads
Eighty-two whole digestive tract samples, 38 partial gut samples, and two fecal
samples were collected from loggerheads in Virginia during 1980, 1983 to 1994, and
1997 and archived at VIMS (Figures 4-6). An additional 46 whole samples and one
partial sample were collected during 2000 to 2002 (Figure 7). The VIMS Sea Turtle
Stranding Database yielded general diet information on another 134 loggerheads from
Virginia (Table 3). A few samples were also collected from Maryland (Figures 4-7) and
the Outer Banks of North Carolina (Figure 8). Six fecal samples and two whole samples
were archived from Maryland during 1984 to 1994, and two fecal samples were collected
in 2002. Six whole samples were collected from North Carolina from 1990 to 1992.
Additional diet information was available on seven loggerheads from Maryland and one
from North Carolina (Table 3). Twenty-three empty digestive tracts were noted in
Virginia from 1980 to 2002 and one was noted for North Carolina in 1994.
The loggerhead samples (n = 185) were distributed geographically as follows
(number of whole samples in parentheses): Western Chesapeake Bay – 111 (91),
Southern Chesapeake Bay – 16 (12), Eastern Shore Bayside – 17 (10), Eastern Shore
Oceanside – 2 (1), Virginia Beach Oceanside – 23 (14), Maryland – 10 (2), and North
Carolina – 6 (6) (Figures 4-9, Table 3). Available loggerhead data (n = 327) were
22
23
FIGURE 4. Approximate locations of all loggerheads (n = 179) and Kemp’s ridleys
(n = 33) from Virginia and Maryland from which samples were collected during
1980 to 2002.
NT
XE
TU
PA
R.
O
POT
OM
AC
R.
O
R.
S
ME
JA
R.
OO
O
OO
OO
O
OO
O
OO
O
O
OO
OO
O
OO
OOOO
O
O
O OO
O
O
O
OO
O
O
O
O
O
OO
O
O
O
O
O
O
O
O
OO O OO
O
OO
O
O
O
O O OOOO
OO
OO
O O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OC
EAN
E AS
TER
N
O
SH
O RE
O
AT L
ANT
IC
RK
YO
CHESAPEAKE BAY
R.
CK
NO
AN
AH
PP
RA
O
O
O
OO O
O
O Loggerhead
O Kemp's ridley
O
O
O
O
N
W
E
S
24
FIGURE 5. Approximate locations of all loggerheads from Virginia and Maryland
from which samples were collected during 1980 to 1989 (n = 60).
NT
R.
PO
TO
MA
C
R.
#
C
NO
AN
AH
PP
RA
#
R.
#
#
1980
1983
1984
1985
#
#
#
#
1986
1987
1988
1989
HO
RE
NS
STE
R
#
#
#
AT
LAN
TIC
OCE
AN
.
S
ME
JA
#
#
EA
R.
R
RK
YO
#
#
##
## ###
##
# #
CHESAPEAKE BAY
K
#
#
#
##
##
#
###
##
#
#
##
#
#
N
#
#
#
#
#
##
#
##
W
E
S
25
FIGURE 6. Approximate locations of all loggerheads from Virginia and Maryland
from which samples were collected during 1990 to 1997 (n = 70).
TU
PA
N
XE
TR
#
.
POT
OM
AC
R.
#
P
RA
H
PA
#
#
SH
OR
E
TER
N
#
R.
CO
C EA
N
K
###
#
###
# #
#
# ##
#
S
ME
JA
R.
#
#
#
1990
1991
1992
#
#
#
1993
1994
1997
#
##
#
##
# # #
#
#
##
#
#
#
#
ATL
AN T
I
R.
R
YO
##
##
E AS
K
OC
#
# #
CHESAPE AKE BAY
N
AN
#
N
#
# #
#
#
#
W
E
S
26
FIGURE 7. Approximate locations of all loggerheads from Virginia and Maryland
from which samples were collected during 2000 to 2002 (n = 49).
PO
TO
MA
CR
.
#
N
AN
AH
PP
RA
#
#
K
OC
EA S
TE R
NS
HO
R
#
R
RK
YO
#
OC
EA
N
#
E
CHESAPEAKE BAY
R.
#
S
ME
JA
##
# #
R.
#
#
#
#
2000
2001
2002
#
##
##
#
#
#
#
##
## #
AT
L AN
TIC
.
#
## #
N
W
#
E
#
#
S
TABLE 3. Composition of loggerhead diet data and samples collected during 1980 to
2002 (excludes 23 empty tracts from Virginia and one from North Carolina).
Turtles with
Diet Data
(Includes
Samples)
Western Bay, Virginia
Southern Bay, Virginia
Eastern Shore Bayside, Virginia
Eastern Shore Oceanside, Virginia
Virginia Beach Oceanside, Virginia
Maryland
North Carolina
Total
179
40
38
9
37
17
7
327
Samples
(Whole, Partial,
Whole
Digestive Tract
and Fecal
Samples)
Samples
111
16
17
2
23
10
6
185
91
12
10
1
14
2
6
136
28
FIGURE 8. Approximate locations of all loggerheads (n = 6: 2 strandings, 4 trawler
takes) and Kemp’s ridleys (n = 2: 1 stranding, 1 trawler take) from North Carolina
from which samples were collected during 1990 to 1992.
O Loggerhead
O Kemp's ridley
ALBEMARLE SOUND
ATLANTIC
OCEAN
PAMLICO SOUND
O
O O
O O O
O
O
N
W
E
S
29
FIGURE 9. Virginia sea turtle stranding regions. From Mansfield et al. 2001.
30
distributed similarly: Western Chesapeake Bay – 179, Southern Chesapeake Bay – 40,
Eastern Shore Bayside – 38, Eastern Shore Oceanside – 9, Virginia Beach Oceanside –
37, Maryland – 17, and North Carolina – 7 (Table 3).
The annual distribution of sample and data collection is shown in Figure 10. The
majority of samples, including 90 of the 169 Virginia samples, were collected in 1990,
1991, 2001, and 2002. More general diet information was collected on stranding data
sheets in other years (Figures 10-11). The monthly distribution of samples (Figure 12) is
consistent with Virginia stranding patterns (Mansfield et al. 2001), and the majority of
samples were collected in May and June. The Maryland samples were collected from
May to October, and all of the North Carolina samples were collected in January and
December.
For Virginia, loggerheads with whole samples (n = 128) ranged in size from 41.6
to 98.5 cm straight carapace length (SCL) (mean = 63.2 cm, standard deviation (SD) =
11.9 cm), and all those with samples (n = 169) ranged in size from 39.0 to 98.5 cm SCL
(mean = 62.6 cm, SD = 11.8 cm) (Figure 13a-b). Virginia loggerheads with data (n =
303) ranged from 33.0 to 98.7 cm SCL (mean = 63.6 cm, SD = 12.3 cm) (Figure 13c).
The majority of these turtles are “benthic immatures” (TEWG 2000), and the size range
is representative of the overall loggerhead strandings in Virginia (Musick and Limpus
1997). Maryland loggerheads with samples (n = 10) measured 57.2 to 98.0 cm SCL
(mean = 73.9 cm, SD = 14.7 cm), and those with data (n = 17) ranged from 47.3 to 98.0
cm SCL (mean = 72.6 cm, SD = 16.6 cm). North Carolina loggerheads sampled (n = 6)
ranged from 42.9 to 64.9 cm SCL, and those with data (n = 7) ranged from 42.9 to 64.9
cm SCL. All measurements presented are straight carapace length measured from notch
31
FIGURE 10. Annual distribution of (a) loggerhead samples (n = 185) and (b)
loggerhead diet data by state (n = 327, excluding 24 empties).
(a)
45
Number of Samples
40
35
30
25
20
15
10
2001
2002
2002
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
Outer Banks, NC
2001
Virginia
1986
1985
1984
1983
1982
1981
0
1980
5
Potomac R. or Solomon's Is., MD
(b)
45
35
30
25
20
15
10
Virginia
Outer Banks, NC
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
0
1981
5
1980
Number of Turtles
40
Potomac R. or Solomon's Is., MD
32
FIGURE 11. Annual distribution of loggerhead samples and data by data type (n =
351, 185 samples, 142 data only, 24 empty).
45
35
30
25
20
15
10
5
Year
Whole Gut
Partial Gut
Fecal Sample
Data only
Empty
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
0
1980
Number of Samples
40
33
FIGURE 12. Distribution of loggerhead samples by month and state (n = 185).
90
Number of Samples
80
70
60
50
40
30
20
10
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Month
Virginia
Outer Banks, NC
Potomac R. or Solomon's Is., MD
Dec
Straight Carapace Length (cm)
Under 30
90.0-94.9
95.0-99.9
Over 99.9
Over 99.9
80.0-84,9
75.0-79.9
70.0-74.9
65.0-69.9
60.0-64.9
55.0-59.9
50.0-54.9
45.0-49.9
40.0-44.9
35.0-39.9
30.0-34.9
95.0-99.9
70
60
50
40
30
20
10
0
90.0-94.9
(c)
85.0-89.9
Straight Carapace Length (cm)
85.0-89.9
80.0-84,9
75.0-79.9
70.0-74.9
65.0-69.9
60.0-64.9
55.0-59.9
50.0-54.9
45.0-49.9
40.0-44.9
35.0-39.9
30.0-34.9
Under 30
Number of Turtles
Number of Turtles
Under 30
Over 99.9
95.0-99.9
90.0-94.9
85.0-89.9
80.0-84,9
75.0-79.9
70.0-74.9
65.0-69.9
60.0-64.9
55.0-59.9
50.0-54.9
45.0-49.9
40.0-44.9
35.0-39.9
30.0-34.9
Number of Turtles
34
FIGURE 13. Size distribution of (a) Virginia loggerhead whole samples (n = 128),
(b) all Virginia loggerhead samples (n = 169), and (c) all Virginia loggerheads with
diet data (n = 303).
(a)
70
60
50
40
30
20
10
0
Straight Carapace Length (cm)
(b)
70
60
50
40
30
20
10
0
35
to notch. This particular measurement was chosen because it was recorded the most
frequently for the turtles included in this analysis. The length conversions presented in
Coles (1999) were used for loggerheads for which notch-to-notch SCL was not recorded.
Due to the small number of samples from the other states, only Virginia data are
discussed further. The gut contents for each loggerhead sampled from Maryland and
North Carolina are listed in Appendix I.
Of those loggerheads sampled in Virginia (n = 169), 74.0% (125) had no obvious
wounds or abnormalities, 11.8% (20) had become entangled in or ingested fishing gear
and/or had constriction marks, and 6.5% (11) had propeller-like or crushing injuries.
Seven appeared to have illnesses, four were probable cold stuns, one turtle had a gaff- or
bullet-like wound, and one appeared to have been struck with a blunt object. This
distribution was similar for all loggerheads from Virginia with diet data (n = 303):
73.3% (222) had no visible abnormalities, 13.2% (40) showed signs of fisheries
interactions, and 7.3% (22) had propeller-like or crushing wounds. In some cases,
however, it is difficult to tell whether injuries have occurred pre- or post-mortem
(personal observation).
The cumulative prey curve for all loggerhead whole samples collected in Virginia
during 1983 to 2002 (n = 128) appears to reach an asymptote (Figure 14). This suggests
that most of the major prey items for the data set as a whole were encountered. Overall,
whole loggerhead samples had an average dry weight of 77.7 g (SD = 115.2 g, median =
42.0 g), and there was an average of 12.9 prey items per whole sample (SD = 17.9,
median = 8.0) and 9.2 large prey items (horseshoe crab, crabs, fish, whelks, moon snails)
(SD = 15.7, median = 5.0) per whole sample. Linear regression indicates that there was a
36
FIGURE 14. Cumulative prey curve for whole loggerhead samples collected in
Virginia during 1983 to 2002 (n = 128). Samples were randomized ten times and
numbers of prey types averaged. Error bars represent ± one standard deviation.
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
20
40
60
80
100
Cumulative Number of Samples
120
140
37
slight positive relationship between loggerhead SCL and total and large prey dry weights
(Figure 15) and numbers (Figure 16).
Interannual diet
The cumulative prey curves for the five-year divisions for whole loggerhead
samples from Virginia are shown in Figure 17. The curves for the two divisions with
more samples, 1988-1992 (n = 49) and 1998-2002 (n = 46), appear to have reached
asymptotes, indicating that all common prey items were probably encountered. The other
two divisions, 1983-1987 (n = 13) and 1993-1997 (n = 20), probably have not reached
asymptotes, but the slopes of the both curves decrease enough by the last sample to
suggest that most common prey items were encountered. As such, all four of these year
groups were included in analyses.
General prey data were compiled from 297 turtles examined during 1983 to 2002
and divided into five-year increments (Figure 18a). These data suggest that horseshoe
crabs occurred less frequently in the Virginia loggerhead diet from 1983 to 1997, while
fish occurred more frequently during this same time period. Crustaceans were present in
at least 50% of samples in each five-year period, and frequency peaked during 1993 to
1997. Correspondence analysis supports the trend from horseshoe crab dominance in
1983 to 1987 to crustacean and fish dominance in later years, and removing the mollusc
data (and thus small, incidental prey items) does not affect this trend (Figure 19). Small
unfamiliar, and rare prey items were probably missed for the 131 turtles examined by
necropsy only (Ruckdeschel and Shoop 1988), and precise prey species information was
not available for all turtles.
38
FIGURE 15. Linear regressions of loggerhead straight carapace length (SCL) versus
(a) total dry weight of Virginia whole samples and (b) dry weights of large prey
items (horseshoe crab, crustaceans, fish, whelks, Atlantic moon snail) in Virginia
whole samples collected during 1983 to 2002 (n = 128).
(a)
Y = -173.201 + 4.18693X
R-Sq = 16.9 %
ANOVA: p = 0.000
Cc Dry
Wt
Total Dry
Weight
(g)
1000
900
800
700
600
500
400
300
200
100
0
40
50
60
70
80
90
100
Cc SCL (cm)
SCL (cm)
Y = -115.465 + 3.06103X
Cc LPDry
Dry Wt
Large Prey
Weight (g)
(b)
R-Sq = 10.0 %
ANOVA: p = 0.000
900
800
700
600
500
400
300
200
100
0
40
50
60
70
Cc SCL (cm)
80
SCL (cm)
90
100
39
FIGURE 16. Linear regressions of loggerhead straight carapace length (SCL) versus
(a) total number of prey items in Virginia whole samples and (b) total number of
large prey items (horseshoe crab, crustaceans, fish, whelks, Atlantic moon snail) in
Virginia whole samples (n = 128).
(a)
Y = -13.1479 + 0.413245X
R-Sq = 7.6 %
ANOVA: p = 0.002
Cc Numbers
Number
of Prey
150
100
50
0
40
50
60
70
80
90
100
Cc
SCL(cm)
(cm)
SCL
(b)
Y = -17.1564 + 0.417960X
R-Sq = 10.1 %
Number
Large Prey
Cc LPofNumber
ANOVA: p = 0.000
140
120
100
80
60
40
20
0
40
50
60
70
80
Cc
SCL (cm)
(cm)
SCL
90
100
40
FIGURE 17. Cumulative prey curves for whole loggerhead samples collected in
Virginia during (a) 1983 to 1987 (n = 13), (b) 1988 to 1992 (n = 49), (c) 1993 to
1997 (n = 20), and (d) 1998 to 2002 (n = 46). Samples were randomized ten times
and numbers of prey types averaged. Error bars represent ± one standard deviation.
(a)
Cumulative Number of Prey Types
60
50
40
30
20
10
0
0
10
20
30
40
50
60
50
60
Cumulative Number of Samples
(b)
Cumulative Number of Prey Types
60
50
40
30
20
10
0
0
10
20
30
40
Cumulative Number of Samples
41
FIGURE 17 (Continued).
Cumulative Number of Prey Types
(c)
60
50
40
30
20
10
0
0
10
20
30
40
50
60
50
60
Cumulative Number of Samples
Cumulative Number of Prey Types
(d) 60
50
40
30
20
10
0
0
10
20
30
40
Cumulative Number of Samples
42
FIGURE 18. Frequency of occurrence of (a) major prey groups in all loggerhead
diet data (n = 297) and (b) major prey items in all loggerhead samples (n = 166)
collected in Virginia during 1983 to 2002, grouped by five-year intervals.
(a)
100
90
80
% Occurrence
70
60
50
40
30
20
10
0
Horseshoe crab
Crustacean
1983-1987 (n = 95)
Mollusc
1988-1992 (n = 82)
Fish
1993-1997 (n = 27)
1998-2002 (n = 93)
(b)
100
90
70
60
50
40
30
20
1983-1987 (n = 38)
1988 - 1992 (n = 61)
1993-1997 (n = 20)
Atlantic moon snail
Busycon whelks
Bony Fish
Lady crab
Purse crab
Rock Crab
Hermit crabs
Spider crabs
0
Callinectes spp.
10
Horseshoe crab
% Occurrence
80
1998-2002 (n = 47)
43
FIGURE 19. Biplots of year division and prey type principal components (PCs) for
PC1 and PC2 of a correspondence analysis using (a) %F values of all four general
diet categories and (b) %F values of three general diet categories from all Virginia
loggerhead diet data collected during 1983 to 2002 (n = 297). PC1 and PC2 account
for 98.86% and 100.0% of the data in (a) and (b), respectively. Number of samples is
in parentheses.
(a)
Component 2
0.8
0.4
1988-1992 (82)
Mollusc
Crustacean
0.0
1983-1987 (95)
Horseshoe crab
1993-1997 (27)
1998-2002 (93)
Fish
0.0
0.4
0.8
Component 1
(b)
0.4
1998-2002 (93)
0.2
Fish
Horseshoe crab
1983-1987 (95)
1993-1997 (27)
Component 2
0.0
Crustacean
-0.2
1988-1992 (82)
-0.4
-0.6
-0.6
-0.4
-0.2
0.0
Component 1
0.2
0.4
44
More specific data were acquired for those turtles that were sampled (Tables 4-8).
Small molluscs, such as blue mussels (Mytilus edulis) and mud snails (Nassarius spp.,
Ilyanassa spp.), as well as various mollusc fragments, plant matter, and debris were
assumed to be consumed incidentally from the benthos (Youngkin and Wyneken, in
press), as gut contents of other prey (Mansour 1992), or as scavengers on other prey
items (Shaver 1991). Larger items considered to be target prey species were horseshoe
crabs, decapod crustaceans, fish, Busycon whelks, and moon snails. Atlantic moon snails
appear to be consumed alive, as indicated by the occasional presence of opercula, but
their empty shells may also be inhabited by hermit crabs (Pagurus spp.) (Frick et al.
2001). Similar trends arise over time for large, frequently occurring prey items in all of
the samples (n = 166) (Figure 18b) and all of the whole samples (n = 128) (Figure 20a).
One notable difference occurs because few whole samples were collected in earlier years,
and the whole samples collected during 1983 to 1987 appear to have a bias towards the
turtles that had eaten fish.
Index of relative importance is probably the most useful measure to compare diets
since “large” prey items varied in size (e.g. horseshoe crab versus hermit crab) (Ferry and
Calliet 1996) (Table 9). Regardless of the measure examined, a shift in loggerhead diet
from horseshoe crab dominance to Callinectes spp. (mostly blue crab, C. sapidus) to fish
dominance (supplemented by hermit crabs) is apparent (Figure 20, Table 9).
Correspondence analyses of all sample data (%F only) and all whole sample data
(especially %IRI) show a general trend along the first principal component (PC1) from
horseshoe crabs to blue, rock, and spider crabs to fish, hermit crabs, and purse crabs
(Figures 21-22).
TABLE 4. Percent occurrence of all prey items found in loggerhead samples (whole and
partial) from Virginia during 1983 to 2002 (n = 166).
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Unidentified portunid
Rock crab
Spider crab spp.
Lady crab
Hermit crab spp.
Purse crab
Mantis shrimp
Other Crustaceans
Acorn barnacle
Crab barnacle
Unidentified barnacle
Unidentified crustacean
Unidentified crustacean tissue
Fish
Bony fish
Elasmobranchs
Unidentified fish tissue
Molluscs
Bivalves
Ark spp.
Common jingle shell
Common razor clam
Hard clam/clam bodies
Little surf clam
Blue mussel
Tellin sp.
Unidentified bivalve
Gastropods
Lunar dove shell
Knobbed and channel whelk
Slipper shell sp.
Wentletrap
19831987
(n=38)
19881992
(n=61)
19931997
(n=20)
39.5
39.5
19.7
19.7
5.0
5.0
19.1
19.1
22.3
22.3
63.2
93.4
80.0
76.6
80.1
Callinectes sapidus
Callinectes sp.
Cancer irroratus
Libinia spp.
Ovalipes ocellatus
Pagurus spp.
Persephona mediterranea
Squilla empusa
50.0
67.2
55.0
25.5
50.0
0.0
8.2
10.0
2.1
4.8
10.5
49.2
20.0
12.8
26.5
26.3
39.3
25.0
23.4
30.1
Balanus sp.
Chelonibia patula
----
Limulus polyphemus
19982002
Overall
(n=47) (n = 166)
0.0
0.0
0.0
8.5
2.4
5.3
11.5
25.0
36.2
18.7
0.0
8.2
5.0
12.8
7.2
5.3
3.3
0.0
4.3
3.6
0.0
4.9
0.0
0.0
1.8
0.0
6.6
0.0
4.3
3.6
2.6
0.0
0.0
2.1
1.2
0.0
0.0
5.0
17.0
5.4
10.5
42.6
10.0
12.8
22.9
21.1
26.2
55.0
61.7
38.6
21.1
23.0
55.0
63.8
38.0
0.0
3.3
0.0
4.3
2.4
0.0
0.0
0.0
2.1
0.6
28.9
72.1
60.0
63.8
58.4
Anadara spp.
Anomia simplex
Ensis directus
Mercenaria mercenaria/unknown
Mulinia lateralis
Mytilus edulis
Tellina sp.
--
5.3
1.6
5.0
6.4
4.2
2.6
0.0
10.0
0.0
1.8
2.6
1.6
0.0
6.4
3.0
2.6
1.6
5.0
0.0
1.8
0.0
6.6
0.0
2.1
3.0
2.6
47.5
15.0
29.8
28.3
Astyris lunata
Busycon spp.
Crepidula sp.
Epitonium sp.
----
2.6
0.0
0.0
0.0
0.6
7.9
18.0
20.0
19.1
16.3
0.0
0.0
0.0
2.1
0.6
7.9
6.6
20.0
10.6
9.6
0.0
1.6
15.0
4.3
3.6
0.0
1.6
0.0
2.1
1.2
Thick-lipped oyster drill
Eastern mud snail
Three-line mud snail
Unidentified mud snail
Spotted northern moon snail
Mottled dog whelk
Atlantic moon snail
Pyramid shell
Atlantic oyster drill
Unidentified gastropod
Other Molluscs
Squid (beaks only)
Unidentified mollusc
Plants
Rockweed
Widgeon grass
Gulfweed sp.
Cordgrass sp.
Sea lettuce
Eelgrass
Unidentified marine plant
Unidentified terrestrial plant
Miscellaneous
Bird feather
Grasshopper
Hydroid
Rocks
Sand dollar
Sponge
Trumpet worm/tubes
Tube worm/tubes
Tunicate
Unidentified bryozoan
Unidentified eggs
Unidentified gelatinous animal
Unidentified polychaete
Unidentified tissue
Anthropogenic Items
Gillnet
Glass
Hook and line gear
Latex
Plastic
Europleura caudata
Ilyanassa obsoleta
Ilyanassa trivittatus
Ilyanassa or Nassarius sp.
Lunatia triseriata
Nassarius vibex
Neverita duplicata
Turbonilla sp.
Urosalpinx cinerea
--
0.0
0.0
0.0
2.1
0.6
0.0
0.0
5.0
2.1
1.2
5.3
4.9
15.0
14.9
9.0
2.6
1.6
0.0
4.3
2.4
0.0
0.0
0.0
2.1
0.6
5.3
6.6
5.0
8.5
6.6
5.3
9.8
5.0
31.9
14.5
0.0
0.0
0.0
2.1
0.6
0.0
0.0
0.0
2.1
0.6
0.0
4.9
15.0
2.1
4.2
Class Cephalopoda
--
0.0
0.0
5.0
2.1
1.2
2.6
0.0
0.0
12.8
4.2
52.6
68.9
80.0
83.0
70.5
0.0
1.6
0.0
4.3
1.8
2.6
0.0
0.0
6.4
2.4
0.0
0.0
5.0
4.3
1.8
0.0
1.6
0.0
2.1
1.2
2.6
3.3
0.0
0.0
1.8
28.9
42.6
50.0
59.6
45.2
42.1
47.5
50.0
57.4
49.4
0.0
1.6
10.0
12.8
5.4
52.6
0.0
59.0
0.0
60.0
5.0
76.6
0.0
62.7
0.6
0.0
0.0
0.0
4.3
1.2
2.6
3.3
0.0
0.0
1.8
10.5
34.4
25.0
40.4
29.5
0.0
0.0
0.0
2.1
0.6
0.0
0.0
10.0
4.3
2.4
2.6
0.0
0.0
0.0
0.6
5.3
8.2
5.0
4.3
6.0
0.0
1.6
15.0
6.4
4.2
0.0
0.0
5.0
0.0
0.6
2.6
0.0
0.0
0.0
0.6
0.0
1.6
0.0
0.0
0.6
0.0
1.6
0.0
0.0
0.6
42.1
31.1
25.0
51.1
38.6
2.6
3.3
5.0
8.5
4.8
0.0
0.0
0.0
2.1
0.6
2.6
1.6
0.0
0.0
1.2
0.0
1.6
5.0
4.3
2.4
0.0
0.0
0.0
2.1
0.6
0.0
0.0
0.0
2.1
0.6
Fucus sp.
Ruppia maritima
Sargassum sp.
Spartina sp.
Ulva lactuca
Zostera marina
--Class Aves
Class Insecta
Sertularia argentea or unknown
-Echinarachnius parma
Phylum Porifera
Pectinaria gouldii
Asabellides oculata
Molgula manhattensis
Class Bryozoa
--Class Polychaeta
-------
TABLE 5. Percent occurrence (%F), percent dry weight (%W), percent number (%N),
and percent index of relative importance (%IRI) of all prey items found in whole
loggerhead gut samples from Virginia during 1983 to 1987 (n = 13). Note: colonial
animals such as hydroids and tube worms were given a count (number) of one.
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Rock crab
Spider crab spp.
Mantis shrimp
Other Crustaceans
Unidentified barnacle
Unidentified crustacean tissue
Fish
Bony fish
Molluscs
Bivalves
Ark spp.
Hard clam/clam bodies
Blue mussel
Unidentified bivalve
Gastropods
Knobbed and channel whelk
Mottled dog whelk
Other Molluscs
Unidentified mollusc
Plants
Widgeon grass
Sea lettuce
Eelgrass
Unidentified marine plant
Miscellaneous
Hydroid
Rocks
Trumpet worm/tubes
Tube worm/tubes
Unidentified tissue
Anthropogenic Items
Glass
Limulus polyphemus
Callinectes sapidus
Cancer irroratus
Libinia spp.
Squilla empusa
---
%F
%W
%N
%IRI
69.2
69.2
27.6
27.6
13.2
13.2
27.5
38.7
53.8
41.8
31.6
38.5
46.2
28.7
21.1
31.4
7.7
0.4
3.9
0.5
23.1
7.0
3.9
3.5
7.7
0.0
1.3
0.1
7.7
0.0
1.3
0.1
7.7
5.6
--
--
38.5
22.5
17.1
14.9
38.5
22.5
17.1
20.9
38.5
4.4
32.9
14.0
Anadara spp.
Mercenaria mercenaria/unknown
Mytilus edulis
--
7.7
0.0
2.6
0.3
7.7
0.2
3.9
0.4
7.7
0.0
3.9
0.4
7.7
1.2
5.3
0.7
Busycon spp.
Nassarius vibex
7.7
1.6
1.3
0.3
7.7
0.1
2.6
0.3
7.7
1.1
13.2
1.5
46.2
0.2
--
--
7.7
0.0
--
--
7.7
0.0
--
--
30.8
0.1
--
--
46.2
0.1
--
--
61.5
3.3
5.3
5.1
7.7
0.0
1.3
0.1
23.1
0.5
--
--
7.7
0.0
1.3
0.1
15.4
0.4
2.6
0.6
38.5
2.4
--
--
7.7
7.7
0.3
0.3
---
---
--
-Ruppia maritima
Ulva lactuca
Zostera marina
-Sertularia argentea or unknown
-Pectinaria gouldii
Asabellides oculata
---
TABLE 6. Percent occurrence (%F), percent dry weight (%W), percent number (%N),
and percent index of relative importance (%IRI) of all prey items found in whole
loggerhead gut samples from Virginia during 1988 to 1992 (n = 49). Note: colonial
animals such as hydroids and tube worms were given a count (number) of one.
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Unidentified portunid
Rock crab
Spider crab spp.
Hermit crab spp.
Purse crab
Mantis shrimp
Other Crustaceans
Acorn barnacle
Crab barnacle
Unidentified crustacean tissue
Fish
Bony fish
Elasmobranchs
Molluscs
Bivalves
Ark spp.
Common razor clam
Hard clam/clam bodies
Little surf clam
Blue mussel
Unidentified bivalve
Gastropods
Knobbed and channel whelk
Slipper shell sp.
Wentletrap
Three-line mud snail
Unidentified mud snail
Mottled dog whelk
Atlantic moon snail
Unidentified gastropod
Plants
Rockweed
%F
%W
%N
%IRI
22.4
22.4
1.7
1.7
1.7
1.7
0.5
1.1
93.9
70.4
52.7
71.5
Callinectes sapidus
Callinectes sp.
Cancer irroratus
Libinia spp.
Pagurus spp.
Persephona mediterranea
Squilla empusa
67.3
34.2
22.2
52.3
Balanus sp.
Chelonibia patula
--
Limulus polyphemus
---
Anadara spp.
Ensis directus
Mercenaria mercenaria/unknown
Mulinia lateralis
Mytilus edulis
-Busycon spp.
Crepidula sp.
Epitonium sp.
Ilyanassa trivittatus
Ilyanassa or Nassarius sp.
Nassarius vibex
Neverita duplicata
-Fucus sp.
8.2
0.1
0.6
0.1
51.0
4.2
12.3
11.6
42.9
13.7
7.4
12.5
12.2
1.0
5.9
1.2
4.1
0.1
0.3
0.0
4.1
0.0
0.3
0.0
6.1
0.0
2.6
0.2
6.1
0.0
1.1
0.1
42.9
17.1
--
--
20.4
6.2
6.3
1.6
18.4
6.1
6.0
3.1
4.1
0.0
0.3
0.0
75.5
5.5
37.9
20.3
2.0
0.0
0.2
0.0
2.0
0.0
0.2
0.0
2.0
0.1
3.7
0.1
6.1
0.0
1.1
0.1
51.0
0.5
21.0
15.1
20.4
0.5
4.3
1.4
6.1
4.2
3.4
0.6
2.0
0.0
0.2
0.0
2.0
0.0
0.3
0.0
6.1
0.0
0.9
0.1
2.0
0.0
0.2
0.0
6.1
0.0
0.8
0.1
10.2
0.2
1.2
0.2
6.1
0.0
0.6
0.1
69.4
0.2
--
--
2.0
0.1
--
--
Cordgrass sp.
Sea lettuce
Eelgrass
Unidentified marine plant
Unidentified terrestrial plant
Miscellaneous
Hydroid
Rocks
Tube worm/tubes
Unidentified gelatinous animal
Unidentified polychaete
Unidentified tissue
Anthropogenic Items
Glass
Hook and line gear
Spartina sp.
Ulva lactuca
Zostera marina
--Sertularia argentea or unknown
-Asabellides oculata
-Class Polychaeta
----
2.0
0.0
--
--
2.0
0.0
--
--
44.9
0.1
--
--
49.0
0.1
--
--
2.0
0.0
--
--
57.1
16.0
1.4
6.1
4.1
0.0
0.3
0.0
30.6
0.6
--
--
10.2
0.1
0.8
0.1
2.0
0.0
0.2
0.0
2.0
0.0
0.2
0.0
30.6
15.3
--
--
4.1
2.0
0.0
0.0
---
---
2.0
0.0
--
--
TABLE 7. Percent occurrence (%F), percent dry weight (%W), percent number (%N),
and percent index of relative importance (%IRI) of all prey items found in whole
loggerhead gut samples from Virginia during 1993 to 1997 (n = 20). Note: colonial
animals such as hydroids and tube worms were given a count (number) of one.
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Unidentified portunid
Rock crab
Spider crab spp.
Hermit crab spp.
Purse crab
Other Crustaceans
Unidentified crustacean
Unidentified crustacean tissue
Fish
Bony fish
Molluscs
Bivalves
Ark spp.
Common jingle shell
Hard clam/clam bodies
Blue mussel
Unidentified bivalve
Gastropods
Knobbed and channel whelk
Slipper shell sp.
Eastern mud snail
Three-line mud snail
Mottled dog whelk
Atlantic moon snail
Unidentified gastropod
Other Molluscs
Squid (beaks only)
Plants
Gulfweed sp.
Eelgrass
Unidentified marine plant
Unidentified terrestrial plant
Limulus polyphemus
Callinectes sapidus
Callinectes sp.
Cancer irroratus
Libinia spp.
Pagurus spp.
Persephona mediterranea
----
Anadara spp.
Anomia simplex
Mercenaria mercenaria/unknown
Mytilus edulis
-Busycon spp.
Crepidula sp.
Ilyanassa obsoleta
Ilyanassa trivittatus
Nassarius vibex
Neverita duplicata
-Class Cephalopoda
Sargassum sp.
Zostera marina
---
%F
%W
%N
%IRI
5.0
5.0
0.4
0.4
0.6
0.6
0.0
0.1
80.0
46.2
36.0
49.2
55.0
13.7
14.6
28.5
10.0
0.2
1.2
0.3
20.0
13.3
6.7
7.3
25.0
13.3
7.3
9.4
25.0
0.2
4.9
2.3
5.0
0.5
0.6
0.1
0.1
5.0
0.2
0.6
10.0
4.8
--
--
55.0
17.9
18.9
15.1
55.0
17.9
18.9
37.0
60.0
27.7
39.0
29.9
5.0
0.9
3.0
0.4
10.0
0.3
1.2
0.3
5.0
19.0
3.0
2.0
15.0
0.0
4.9
1.3
20.0
1.8
6.7
3.1
20.0
2.8
4.3
2.6
15.0
1.3
5.5
1.9
5.0
0.1
0.6
0.1
15.0
0.1
2.4
0.7
5.0
0.1
0.6
0.1
5.0
0.1
1.2
0.1
15.0
1.0
2.4
1.0
5.0
0.0
3.0
0.3
80.0
0.4
--
--
5.0
0.1
--
--
50.0
0.1
--
--
50.0
0.2
--
--
10.0
0.0
--
--
Miscellaneous
Bird feather
Rocks
Sponge
Tube worm/tubes
Tunicate
Unidentified bryozoan
Unidentified tissue
Anthropogenic Items
Hook and line gear
Class Aves
-Phylum Porifera
Asabellides oculata
Molgula manhattensis
Class Bryozoa
---
60.0
5.0
7.2
0.0
5.5
0.6
5.7
0.1
25.0
0.1
--
--
10.0
0.8
1.2
0.4
5.0
0.0
0.6
0.1
15.0
0.1
2.4
0.7
5.0
0.0
0.6
0.1
25.0
6.2
--
--
5.0
0.1
--
--
5.0
0.1
--
--
TABLE 8. Percent occurrence (%F), percent dry weight (%W), percent number (%N),
and percent index of relative importance (%IRI) of all prey items found in whole
loggerhead gut samples from Virginia during 1998 to 2002 (n = 46). Note: colonial
animals such as hydroids and tube worms were given a count (number) of one.
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Unidentified portunid
Rock crab
Spider crab spp.
Lady crab
Hermit crab spp.
Purse crab
Mantis shrimp
Other Crustaceans
Crab barnacle
Unidentified barnacle
Unidentified crustacean
Unidentified crustacean tissue
Fish
Bony fish
Elasmobranchs
Unidentified fish tissue
Molluscs
Bivalves
Ark spp.
Common razor clam
Little surf clam
Blue mussel
Unidentified bivalve
Gastropods
Lunar dove shell
Knobbed and channel whelk
Slipper shell sp.
Wentletrap
Thick-lipped oyster drill
Eastern mud snail
Three-line mud snail
Unidentified mud snail
%F
%W
%N
%IRI
19.6
19.6
5.8
5.8
1.6
1.6
1.0
2.4
78.3
36.9
47.4
47.9
Callinectes sapidus
Callinectes sp.
Cancer irroratus
Libinia spp.
Ovalipes ocellatus
Pagurus spp.
Persephona mediterranea
Squilla empusa
26.1
2.2
4.4
2.8
Chelonibia patula
----
Limulus polyphemus
----
Anadara spp.
Ensis directus
Mulinia lateralis
Mytilus edulis
-Astyris lunata
Busycon spp.
Crepidula sp.
Epitonium sp.
Europleura caudata
Ilyanassa obsoleta
Ilyanassa trivittatus
Ilyanassa or Nassarius sp.
2.2
0.0
0.1
0.0
13.0
0.3
1.6
0.4
23.9
17.3
7.3
9.7
8.7
1.8
7.7
1.4
37.0
1.4
20.2
13.1
13.0
2.2
3.7
1.3
4.3
0.0
0.3
0.0
4.3
0.0
0.7
0.0
2.2
0.0
0.4
0.0
17.4
0.0
1.0
0.3
13.0
11.5
--
--
63.0
43.7
15.0
26.9
63.0
40.8
14.6
57.2
4.3
0.4
0.4
0.1
2.2
2.5
--
--
65.2
4.7
34.9
18.8
6.5
0.0
0.4
0.0
6.5
0.0
0.4
0.0
2.2
0.0
1.4
0.1
28.3
0.1
3.9
1.9
17.4
0.1
2.6
0.8
2.2
0.0
0.1
0.0
10.9
2.6
8.0
1.9
4.3
0.1
1.3
0.1
2.2
0.0
0.4
0.0
2.2
0.1
0.3
0.0
2.2
0.0
0.1
0.0
15.2
0.2
5.1
1.3
4.3
0.0
0.7
0.0
Spotted northern moon snail
Mottled dog whelk
Atlantic moon snail
Pyramid shell
Atlantic oyster drill
Unidentified gastropod
Other Molluscs
Squid (beaks only)
Unidentified mollusc
Plants
Rockweed
Widgeon grass
Gulfweed sp.
Cordgrass sp.
Eelgrass
Unidentified marine plant
Unidentified terrestrial plant
Miscellaneous
Grasshopper
Rocks
Sand dollar
Sponge
Tube worm/tubes
Tunicate
Unidentified tissue
Anthropogenic Items
Hook and line gear
Latex
Plastic
Lunatia triseriata
Nassarius vibex
Neverita duplicata
Turbonilla sp.
Urosalpinx cinerea
-Class Cephalopoda
-Fucus sp.
Ruppia maritima
Sargassum sp.
Spartina sp.
Zostera marina
--Class Insecta
-Echinarachnius parma
Phylum Porifera
Asabellides oculata
Molgula manhattensis
-----
4.3
0.0
0.1
0.0
8.7
0.0
0.5
0.1
32.6
1.3
7.4
4.7
2.2
0.0
0.1
0.0
2.2
0.0
0.1
0.0
2.2
0.0
0.1
0.0
2.2
0.0
0.1
0.0
13.0
0.1
1.6
0.4
87.0
0.2
--
--
4.3
0.0
--
--
6.5
0.0
--
--
4.3
0.0
--
--
2.2
0.0
--
--
60.9
0.1
--
--
56.5
0.1
--
--
13.0
0.0
--
--
76.1
4.3
8.5
0.0
1.2
0.3
5.3
0.0
39.1
0.6
--
--
2.2
0.0
0.1
0.0
4.3
0.0
0.3
0.0
2.2
0.0
0.1
0.0
6.5
0.0
0.4
0.0
52.2
7.7
--
--
6.5
0.3
--
--
4.3
0.2
--
--
2.2
0.0
--
--
2.2
0.0
--
--
54
FIGURE 20. (a) Frequency of occurrence, (b) percent dry weight, (c) percent
number, and (d) percent index of relative importance (IRI) in whole loggerhead gut
samples collected in Virginia from 1983 to 2002 (n = 128), group ed by five-year
intervals.
(a)
100
90
80
% Occurrence
70
60
50
40
30
20
1983-1987 (n = 13)
1988 - 1992 (n = 49)
1993-1997 (n = 20)
Atlantic moon
snail
Busycon whelks
Bony Fish
Lady crab
Purse crab
Rock Crab
Hermit crabs
Callinectes spp.
Horseshoe crab
0
Spider crabs
10
1998-2002 (n = 46)
(b)
50
30
20
1983-1987 (n = 13)
1988 - 1992 (n = 49)
1993-1997 (n = 20)
Atlantic moon
snail
Busycon whelks
Bony Fish
Lady crab
Purse crab
Rock Crab
Hermit crabs
Spider crabs
0
Callinectes spp.
10
Horseshoe crab
% Dry Weight
40
1998-2002 (n = 46)
0
1983-1987 (n = 38)
1988 - 1992 (n = 61)
1993-1997 (n = 20)
Atlantic moon
snail
Busycon whelks
1993-1997 (n = 20)
Bony Fish
Lady crab
1988 - 1992 (n = (49)
Purse crab
Rock Crab
1983-1987 (n = 13)
Hermit crabs
Spider crabs
Callinectes spp.
Atlantic moon
snail
Busycon whelks
Bony Fish
Lady crab
Purse crab
Rock Crab
Hermit crabs
Spider crabs
Callinectes spp.
Horseshoe crab
0
Horseshoe crab
% IRI
% Number
55
FIGURE 20 (Continued).
(c)
50
40
30
20
10
1998-2002 (n = 46)
(d)
100
90
80
70
60
50
40
30
20
10
1998-2002 (n = 47)
TABLE 9. Prey species with five highest percent index of relative importance values for
whole loggerheads samples from Virginia during 1983 to 2002 (n = 128).
1983-1987 (n=13)
Horseshoe crab (38.7%)
Blue crab (31.4%)
Bony fish (20.9%)
Spider crab spp. (3.5%)
Unidentified mollusc (1.5%)
1988-1992 (n=49)
Blue crab (52.3%)
Blue mussel (15.1%)
Spider crab spp. (12.5%)
Rock crab (11.6%)
Bony fish (3.1%)
1993-1997 (n=20)
1998-2002 (n=46)
Bony fish (37.0%)
Blue crab (28.5%)
Spider crab spp. (9.4%)
Rock crab (7.3%)
Unidentified bivalve (3.1%)
Bony fish (57.2%)
Hermit crab spp. (13.1%)
Spider crab spp. (9.7%)
Atlantic moon snail (4.7%)
Blue crab (2.8%)
57
FIGURE 21. Biplot of year division and prey type principal components (PCs) for
PC1 and PC2 of a correspondence analysis using %F values for major prey items
from all loggerhead samples collected in Virginia during 1983 to 2002 (n = 166).
PC1 and PC2 account for 84.28% of the data. Number of samples is in parentheses.
1.5
Component 2
1.0
Horseshoe crab
Lady crab
0.5
1983-1987 (38)
Atlantic moon snail
1998-2002 (47)
Spider crab spp.
0.0
Bony fish
Callinectes spp.
Hermit
1988-1992 (61)
Purse crab
crab spp.
Busycon whelk spp.
Rock crab
1993-1997 (20)
0.0
0.5
Component 1
1.0
1.5
58
FIGURE 22. Biplots of year division and prey type principal components (PCs) for
PC1 and PC2 of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d)
%IRI values for major prey items from all whole loggerhead samples from Virginia
during 1983 to 2002 (n = 128). PC1 and PC2 account for 86.77%, 88.22%, 93.14%,
and 96.03% of the data in (a), (b), (c), and (d), respectively. Number of samples is in
parentheses.
(a)
1.0
Lady crab
Component 2
Horseshoe crab
0.5
1983-1987 (13)
Bony fish
1998-2002 (46)
Atlantic moon snail
Purse crab
Busycon whelk spp. Hermit crab spp.
0.0
(20)
Spider crab1993-1997
spp.
Callinectes spp.
1988-1992 (49)
-0.5
Rock crab
-0.5
0.0
0.5
1.0
Component 1
(b)
Horseshoe crab
1
1983-1987 (13)
Component 2
Callinectes spp.
Atlantic
0 moon snail &
Purse
crab
Atlantic
Purse
Lady
moon
crab
crab
snail
1998-2002Bony
(46) fish
1988-1992 (49)
Hermit Busycon
crab spp. whelk spp.
Spider crab spp.
1993-1997 (20)
-1
Rock crab
-1
0
Component 1
1
59
FIGURE 22 (Continued).
Horseshoe crab
(c)
0.5
1983-1987 (13)
Lady crab
Bony fish
Component 2
Purse crab
1998-2002 (46)
Atlantic moon snail
0.0
Hermit crab
Busycon
spp. whelk spp.
Callinectes spp.
Spider1993-1997
crab spp. (20)
1988-1992 (49)
Rock crab
-0.5
-1.0
-1.5
-1.5
-1.0
-0.5
0.0
0.5
Component 1
Horseshoe crab
(d)
1
1983-1987 (13)
Component 2
Atlantic moon snail, lady crab &
Atlantic
Purse
Lady
Purse
moon
crab
crab
crab
snail
0
Bony fish
1998-2002 (46)
Hermit crab spp.
1993-1997 (20) Callinectes spp.
Spider
crab spp.
Busycon whelk
spp.
1988-1992 (49)
Rock crab
-1
-1
0
Component 1
1
60
Interestingly, Atlantic moon snails tended to group with hermit crabs in the biplots,
suggesting that the crabs are using the shells.
The fish species encountered in all samples (partial and whole) are listed in Table
10. Atlantic menhaden (Brevoortia tyrannus), striped bass (Morone saxatilis) and
bluefish (Pomatomus saltatrix) were encountered in all four of the five-year periods.
Menhaden and croaker (Micropogonias undulatus) were the two most frequently
encountered fish species during 1993-1997 and 1998-2002. Batoids (skates and rays)
were encountered in several samples, and a sharpnose shark (Rhizoprionodon
terraenovae) was identified from teeth found in a sample from 2001.
Size-specific diet
As with the annual Virginia data, only the cumulative prey curves for size classes
with larger numbers of whole samples (50.0-59.9 cm and 60.0-69.9 cm SCL) reached
asymptotes (Figure 23); however, data for the smaller size class and the three larger ones
were still examined (Figure 24). Although sample size discrepancies should be kept in
mind, horseshoe crab, hermit crab, and whelk consumption (and %IRI) increased with
size (and therefore age) of loggerheads, while blue crab consumption appeared to
decrease with size. Turtles in the middle size classes consumed bony fish most
frequently, and none of the largest turtles (90.0-99.9 cm SCL) had consumed fish.
Correspondence analysis of %F values separated loggerheads into three groups along
PC1: 40.0-69.9 cm SCL, 70.0-89.9 cm SCL, and 90.0-99.9 cm SCL (Figure 25a).
Correspondence analyses using the %W, %N, and %IRI values separated the 90.0-99.9
cm SCL turtles from all other size classes (Figure 25b-d). By calculating the Schoener
TABLE 10. Percent occurrence of all fish species found in loggerhead samples (whole
and partial) from Virginia during 1983 to 2002 (n = 166).
Bony Fish
Striped anchovy
Menhaden
Seatrout sp.
Spot
Croaker
Striped bass
Oyster toadfish
Bluefish
Unidentified clupeid
Unidentified flatfish
Unidentified bony fish
Elasmobranchs
Clearnose skate
Sharpnose shark
Stingray sp.
Skate egg case
Unidentified batoid
19831987
(n=38)
19881992
(n=61)
19931997
(n=20)
19982002
(n=47)
Anchoa hepsetus
Brevoortia tyrannus
Cynoscion sp.
Leiostomus xanthurus
Micropogonias undulatus
Morone saxatilis
Opsanus tau
Pomatomus saltatrix
Family Clupeidae
Order Pleuronectiformes
--
0.0
2.6
0.0
0.0
0.0
5.3
0.0
7.9
0.0
2.6
10.5
0.0
16.4
1.6
0.0
0.0
1.6
1.6
4.9
0.0
1.6
9.8
5.0
35.0
5.0
0.0
20.0
5.0
0.0
10.0
0.0
0.0
20.0
0.0
23.4
10.6
2.1
40.4
4.3
0.0
4.3
6.4
0.0
17.0
Raja eglanteria
Rhizoprionodon terraenovae
Family Dasyatidae
Family Rajidae
--
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.6
1.6
0.0
0.0
0.0
0.0
0.0
0.0
2.1
2.1
0.0
0.0
2.1
62
FIGURE 23. Cumulative prey curves for whole samples from Virginia loggerheads
with straight carapace lengths of (a) 40.0 to 49.9 cm (n = 13), (b) 50.0 to 59.9 cm (n
= 44), (c) 60.0 to 69.9 cm (n = 48), (d) 70.0 to 79.9 cm (n = 9), (e) 80.0 to 89.9 cm (n
= 8), and (f) 90.0 to 99.9 cm (n = 6). Samples were randomized ten times and
numbers of prey types averaged. Error bars represent ± one standard deviation.
Cumulative Number of Prey Types
(a) 50
40
30
20
10
0
0
10
20
30
40
50
40
50
Cumulative Number of Samples
Cumulative Number of Prey Types
(b) 50
40
30
20
10
0
0
10
20
30
Cumulative Number of Samples
63
FIGURE 23 (Continued).
Cumulative Number of Prey Types
(c)
50
40
30
20
10
0
0
10
20
30
40
50
40
50
Cumulative Number of Samples
Cumulative Number of Prey Types
(d)
50
40
30
20
10
0
0
10
20
30
Cumulative Number of Samples
64
FIGURE 23 (Continued).
Cumulative Number of Prey Types
(e)
50
40
30
20
10
0
0
10
20
30
40
50
40
50
Cumulative Number of Samples
Cumulative Number of Prey Types
(f)
50
40
30
20
10
0
0
10
20
30
Cumulative Number of Samples
65
FIGURE 24. (a) Frequency of occurrence and (b) percent index of relative
importance (IRI) in whole loggerhead gut samples collected in Vi rginia during 1983
to 2002 (n = 128), grouped by ten-centimeter size classes (SCL).
(a)
100
90
% Occurrence
80
70
60
50
40
30
20
40.0-49.9 cm (n=13)
50-59.9 cm (n=44)
60-69.9 cm (n=48)
70-79.9 cm (n=9)
80.0-89.0 cm (n=8)
90.0-99.9 cm (n=6)
Atlantic moon
snail
Busycon whelks
Bony fish
Rock crab
Hermit crabs
Callinectes spp.
Horseshoe crab
0
Spider crabs
10
(b)
100
90
80
60
50
40
30
20
40.0-49.9 cm (n=13)
70-79.9 cm (n=9)
50-59.9 cm (n=44)
80.0-89.0 cm (n=8)
60-69.9 cm (n=48)
90.0-99.9 cm (n=6)
Atlantic moon
snail
Busycon whelks
Bony fish
Rock crab
Hermit crabs
Spider crabs
0
Callinectes spp.
10
Horseshoe crab
%IRI
70
66
FIGURE 25. Biplots of size class and prey type principal components (PCs) for PC1
and PC2 of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia during
1983 to 2002 (n = 128). Label represents lower end of size class (e.g. 40 includes
samples from 40.0 to 49.9 cm). PC1 and PC2 account for 95.23%, 86.60%, 89.38%,
and 82.46% of the data in (a), (b), (c), and (d), respectively. Number of samples is in
parentheses.
(a)
0.5
Busycon whelk spp.
40 (13)
Spider crab spp.
Callinectes spp.
90 (6)
50 (45)
Component 2
60 (48)
0.0
80 (7)
Bony fish
Hermit crab spp. Rock crab
Horseshoe crabAtl. moon snail
70 (9)
-0.5
-1.0
-1.0
-0.5
0.0
0.5
Component 1
70 (9)
Spider crab spp.
(b)
Atl. moon snail
50 (45)
Bony fish
0
Horseshoe crab
90 (6)
Busycon whelk spp.
Rock crab
80 (7)
40 (13)
60 (48)
Component 2
Hermit crab spp.
Callinectes spp.
-1
-2
-2
-1
Component 1
0
67
FIGURE 25 (Continued).
80 (7)
(c)
Component 2
1
Hermit crab spp.
Atl. moon70
snail
(9)
Horseshoe crab
Spider crab spp.
0
90 (6)
Busycon whelk spp.
Rock crab
40 (13)
Callinectes
50 (45) spp.
60 (48)
Bony fish
-1
-1
0
1
Component 1
Hermit crab spp.
(d)
80 (7)
1
Atl. moon snail
Horseshoe crab
Component 2
70 (9)
0
crab
SpiderRock
crab spp.
Bony fish
50 (45) spp.
Callinectes
60 (13)
(48)
40
90 (6)
Busycon whelk spp.
-1
-2
-2
-1
0
Component 1
1
68
(1970) index using average percent dry weight values from whole samples, a diet overlap
of 80.5% was found between loggerheads 40.0-69.9 cm SCL (n = 106) and those 70.099.9 cm SCL (n = 22) for the more prominent prey items (horseshoe crabs, Callinectes
spp., spider, hermit, and rock crabs, bony fish, whelks, and Atlantic moon snails).
Sex-specific diet
The cumulative prey curves for whole samples collected in Virginia from female,
male, and unknown sex loggerheads all reached reasonable asymptotes (Figure 26). The
ratio of females to males examined in this study was almost three to one, whereas
reported values for Virginia have been about two to one (Musick et al. 1984; Bellmund et
al. 1987). Discounting the unknown turtles, there did not appear to be any major diet
differences between female (n = 73) and male (n = 26) loggerheads (Figure 27).
Examination of CA biplots along PC1 yielded the same conclusion (Figure 28). The
perceived difference in whelk %IRI was due to an adult male sample containing 57
Busycon whelk opercula. An 89.4% overlap was found between the sexes using the
Schoener (1970) index and average percent dry weight values for horseshoe crabs,
Callinectes spp., spider, hermit, and rock crabs, bony fish, whelks, and Atlantic moon
snails. If whelks were excluded, the overlap was 92.1%.
Interseasonal diet
Samples were also grouped according to season. Only three Virginia loggerhead
samples were collected in Virginia during winter months (December to February).
69
FIGURE 26. Cumulative prey curves for whole loggerhead samples from
Virginia taken from (a) females (n = 73), (b) males (n = 26), and (c) unknowns (n
= 29). Samples were randomized ten times and numbers of prey types averaged.
Error bars represent ± one standard deviation.
(a)
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
60
70
80
60
70
80
Cumulative Number of Samples
(b)
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
10
20
30
40
50
Cumulative Number of Samples
(c)
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
10
20
30
40
50
Cumulative Number of Samples
70
FIGURE 27. (a) Frequency of occurrence and (b) percent index of relative
importance (IRI) in whole loggerhead gut samples collected in Vi rginia during 1983
to 2002 (n = 128), grouped by sex of turtle.
(a)
100
90
% Occurrence
80
70
60
50
40
30
20
Busycon whelks
Atlantic moon
snail
Atlantic moon
snail
Bony fish
Rock crab
Male (n = 26)
Busycon whelks
Female (n = 73)
Hermit crabs
Callinectes spp.
Horseshoe crab
0
Spider crabs
10
Unknown (n = 29)
(b)
100
90
80
70
50
40
30
20
Female (n = 73)
Male (n = 26)
Bony fish
Rock crab
Hermit crabs
Spider crabs
0
Callinectes spp.
10
Horseshoe crab
%IRI
60
Unknown (n = 29)
71
FIGURE 28. Biplots of turtle sex and prey type principal components (PCs) for PC1
and PC2 of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia during
1983 to 2002 (n = 128). PC1 and PC2 account for 100% of the data in all four
analyses. Number of samples is in parentheses.
(a)
0.6
0.5
0.4
Component 2
0.3
Busycon whelks
0.2
0.1
Spider crabs
Hermit crabs
Rock
crab
Bony
fish
Unknown (29)
Male (26)
0.0
Callinectes spp.
Horseshoe crab
Female (73)
Atlantic moon snail
-0.1
-0.2
-0.3
-0.3 -0.2 -0.1 0.0 0.1 0.2
0.3 0.4
0.5 0.6
Component 1
(b)
Busycon whelks
0.5
Male (26)
Horseshoe crab
Spider crabs
Hermit crabs
Component 2
Rock crab
0.0
Unknown (29)
Callinectes spp.
Bony fish
Female (73)
-0.5
Atlantic moon snail
-0.5
0.0
Component 1
0.5
72
FIGURE 28 (Continued).
(c)
Spider crabs
Unknown (29)
Rock crab
Busycon whelks
Atlantic moon snail
Male (26)
Component 2
0.0
Hermit crabs
Bony fish
Callinectes spp.
Horseshoe crab
Female (73)
-0.5
-1.0
-1.0
-0.5
0.0
Component 1
(d)
Atlantic moon snail
Female (73)
Bony fish
Callinectes spp.
Unknown (29)
Rock crab
Component 2
0.0
Hermit crabs
Spider crabs
Male (26)Horseshoe crab
-0.5
-1.0
Busycon whelks
-1.0
-0.5
Component 1
0.0
73
Therefore, diet was examined among only spring (March to May), summer (June to
August), and fall (September to November). The spring and summer cumulative prey
curves reached asymptotes, while the fall curve appeared close to an asymptote (Figure
29). Although no major prey differences were apparent, the spring and summer samples
were dominated slightly by Callinectes spp. and fish, while horseshoe crabs and hermit
crabs slightly dominated fall diet (Figure 30). Spring and summer grouped away from
fall in CA biplots (Figure 31).
Kemp’s Ridleys
Nine partial digestive tract samples and one fecal sample were collected from
Kemp’s ridleys in Virginia and archived at VIMS during 1987 to 1994. Five whole
ridley gut samples were archived from 1991 to 1994, and 18 were collected from 2000 to
2002 (Figures 4, 32-35, Table 11). Two whole samples were collected from North
Carolina during 1990 to 1991 (Figure 8). Additional data were available on 26 Kemp’s
ridleys from Virginia and one from North Carolina (Table 11). Three ridleys from
Virginia and one from North Carolina had empty digestive tracts.
The Kemp’s ridley samples (n = 35) were distributed geographically as follows
(number of whole samples in parentheses): Western Chesapeake Bay – 13 (9), Southern
Chesapeake Bay – 4 (3), Eastern Shore Bayside – 6 (6), Virginia Beach Oceanside – 10
(5), and North Carolina – 2 (2) (Figures 32-34, Table 11). Available Kemp’s ridley data
(n = 62) were distributed similarly: Western Chesapeake Bay – 19, Southern Chesapeake
Bay – 15, Eastern Shore Bayside – 11, Virginia Beach Oceanside – 14, and North
Carolina – 3 (Table 11).
74
FIGURE 29. Cumulative prey curves for whole loggerhead samples from Virginia
during (a) Spring (March to May, n = 47), (b) Summer (June to August, n = 64), and
(c) Fall (September to November, n = 14). Samples were randomized ten times and
numbers of prey types averaged. Error bars represent ± one standard deviation.
(a)
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
60
70
60
70
Cumulative Number of Samples
(b)
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
10
20
30
40
50
Cumulative Number of Samples
(c)
Cumulative Number of Prey Types
70
60
50
40
30
20
10
0
0
10
20
30
40
50
Cumulative Number of Samples
75
FIGURE 30. (a) Frequency of occurrence and (b) percent index of relative
importance (IRI) in whole loggerhead gut samples collected in Vi rginia during 1983
to 2002 (n = 128), grouped by season.
(a)
100
90
80
% Occurrence
70
60
50
40
30
20
Spring (Mar - May, n = 47)
Summer (June - Aug, n = 64)
Atlantic moon
snail
Busycon whelks
Bony fish
Rock crab
Hermit crabs
Spider crabs
Callinectes spp.
0
Horseshoe crab
10
Fall (Sept - Nov, n = 14)
(b)
100
90
80
70
50
40
30
20
Spring (Mar - May, n = 47)
Summer (June - Aug, n = 64)
Atlantic moon
snail
Busycon whelks
Bony fish
Rock crab
Hermit crabs
Spider crabs
0
Callinectes spp.
10
Horseshoe crab
%IRI
60
Fall (Sept - Nov, n = 14)
76
FIGURE 31. Biplots of season and prey type principal components (PCs) for PC1
and PC2 of a correspondence analysis using (a) %F, (b) %W, (c) %N, and (d) %IRI
values for major prey items from all whole loggerhead samples from Virginia during
1983 to 2002 (n = 125, spring, summer, and fall only). PC1 and PC2 account for
100% of the data in all four analyses. Number of samples is in parentheses.
(a)
0.5
Rock crab
Busycon whelks
Component 2
Spring (47)
Fall (14)
Hermit crabs
Atlantic moon snail
Spider crabs
0.0
Callinectes spp.
Horseshoe crab
Bony fish
Summer (64)
-0.5
-0.5
0.0
0.5
Component 1
(b)
0.5
Component 2
Callinectes spp.
Summer (64)
0.0
Horseshoe crab
Spider crabs
Fall (14)
Hermit crabs
Bony fish
Spring (47)
-0.5
Rock crab
Atlantic moon snail
Busycon whelks
-0.5
0.0
Component 1
0.5
77
FIGURE 31 (Continued).
Busycon whelks
(c)
Rock crab
Component 2
0.5
Spring (47)
Hermit
crabs
Fall (14)
Spider crabs
0.0
Atlantic moon snail
Horseshoe crab
Callinectes spp.
Bony fish
Summer (64)
-0.5
-0.5
0.0
0.5
Component 1
(d)
0.5
Summer (64)
Callinectes spp.
Horseshoe crab
Hermit crabs
Fall (14)
Bony fish
Component 2
0.0
Atlantic moon snail
Spider crabs
Spring (47)
-0.5
Busycon whelks
Rock crab
-1.0
-1.0
-0.5
Component 1
0.0
0.5
78
FIGURE 32. Approximate locations of all Kemp’s ridleys from Virginia from which
samples were collected during 1987 to 1989 (n = 6).
PO
TO
MA
C
R.
HO
RE
RN
S
STE
.
AT
LA N
TIC
OC
EAN
.
EA
KR
R
RK
YO
CHESAPEAKE BAY
C
NO
AN
AH
PP
RA
#
#
SR
ME
JA
.
N
#
#
#
#
1987
1988
1989
W
##
E
S
79
FIGURE 33. Approximate locations of all Kemp’s ridleys from Virginia from which
samples were collected during 1991 to 1994 (n = 9).
PO
TO
MA
C
R.
NO
AN
AH
PP
RA
HO
RE
ER
NS
.
SR
ME
JA
AT
LAN
TIC
OC
EA N
EA
ST
.
CHESAPEAKE BAY
R
CK
R
RK
YO
#
#
#
#
#
.
N
#
#
#
1991
#
1992
#
1994
#
#
W
E
S
80
FIGURE 34. Approximate locations of all Kemp’s ridleys from Virginia from which
samples were collected during 2000 to 2002 (n = 18).
PO
TO
MA
C
R.
NO
AN
AH
PP
RA
HO
RE
ER
NS
.
AT
LAN
TIC
OC
EA N
EA
ST
.
CHESAPEAKE BAY
R
CK
R
RK
YO
#
#
SR
ME
JA
.
#
##
#
#
#
#
#
#
N
#
# #
#
#
#
#
2000
2001
2002
W
E
#
#
S
TABLE 11. Composition of Kemp’s ridley diet data and samples collected during 1987
to 2002 (excludes three empty tracts from Virginia and one from North Carolina).
Turtles with
Diet Data
(Includes
Samples)
Western Bay, Virginia
Southern Bay, Virginia
Eastern Shore Bayside, Virginia
Eastern Shore Oceanside, Virginia
Virginia Beach Oceanside, Virginia
Maryland
North Carolina
Total
19
15
11
0
14
0
3
62
Samples
(Whole, Partial,
Whole
Digestive Tract
and Fecal
Samples)
Samples
13
4
6
0
10
0
2
35
9
3
6
0
5
0
2
25
82
FIGURE 35. Annual distribution of (a) Kemp’s ridley samples (n = 35) and (b)
Kemp’s ridley diet data by state (n = 62, excluding 4 empties).
(a)
10
Number of Samples
9
8
7
6
5
4
3
2
1
1996
1997
1998
1999
2000
2001
2002
1997
1998
1999
2000
2001
2002
1995
1994
1993
1992
1996
Virginia
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
0
Outer Banks, NC
(b)
18
14
12
10
8
6
4
Virginia
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
0
1981
2
1980
Number of Turtles
16
Outer Banks, NC
83
The majority of the Kemp’s ridley samples, including 18 of the 33 Virginia
samples, were collected during 2000 to 2002 (Figure 35). Some general diet information
was collected on stranding data sheets in other years (Figures 35-36). The monthly
distribution of samples (Figure 37) is consistent with Virginia spring and fall stranding
peaks (Mansfield et al. 2001), and the vast majority of samples were collected in May,
June, and October. The two North Carolina samples were collected in December.
Kemp’s ridleys from Virginia with whole samples taken (n = 23) ranged in size
from 23.1 to 49.9 cm SCL (mean = 36.7 cm, SD = 7.3 cm) (Figure 38a), and all those
with samples (n = 33) ranged in size from 23.1 to 53.4 cm SCL (mean = 37.9 cm, SD =
8.5 cm) (Figure 38b). Virginia Kemp’s ridleys with data (n = 59) ranged from 23.0 to
53.4 cm SCL (mean = 36.0 cm, SD = 8.6 cm) (Figure 38c). All of the Kemp’s ridleys
examined were “benthic immatures” (TEWG 2000), and the size range included all but
the largest ridleys encountered in Virginia (Musick and Limpus 1997). The North
Carolina ridleys sampled were 30.0 cm and 38.5 cm SCL. As with the loggerhead data,
all measurements presented are notch-to-notch SCL, and conversions presented in Coles
(1999) were used for ridleys for which this measurement was not available.
Only Virginia data are discussed further. The contents of the two North Carolina
Kemp’s ridley samples are listed in Appendix II.
Of those Kemp’s ridleys from Virginia with samples (n = 33), 78.8% (26) had no
obvious abnormalities, and 15.2% (5) had propeller-like or crushing injuries. One ridley
sampled had ingested hook and line fishing gear, and one was an incidental dredge take.
This distribution was similar for all Virginia Kemp’s ridleys with diet information
84
FIGURE 36. Annual distribution of Kemp’s ridley samples and data by data type
(n = 66, 35 samples, 27 data only, 4 empty).
18
16
12
10
8
6
4
2
Year
Whole Gut
Partial Gut
Fecal Sample
Data Only
Empty
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
0
1980
# of Samples
14
85
FIGURE 37. Distribution of Kemp’s ridley samples by month and state (n = 35).
11
10
9
# of Samples
8
7
6
5
4
3
2
1
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Month
Virginia
Outer Banks, NC
Sep
Oct
Nov
Dec
86
FIGURE 38. Size distribution of (a) Virginia Kemp’s ridley whole samples (n = 23),
(b) all Virginia Kemp’s ridley samples (n = 33), and (c) all Virginia Kemp’s ridleys
with diet data (n = 59).
(a)
Number of Turtles
10
8
6
4
2
Over 54.9
50.0-54.9
45.0-49.9
40.0-44.9
35.0-39.9
30.0-34.9
25.0-29.9
20.0-24.9
Under 20
0
Straight Carapace Length (cm)
(b)
Number of Turtles
10
8
6
4
50.0-54.9
Over 54.9
50.0-54.9
Over 54.9
45.0-49.9
40.0-44.9
35.0-39.9
30.0-34.9
25.0-29.9
20.0-24.9
0
Under 20
2
Straight Carapace Length (cm)
(c)
15
10
45.0-49.9
40.0-44.9
35.0-39.9
30.0-34.9
25.0-29.9
0
20.0-24.9
5
Under 20
Number of Turtles
20
Straight Carapace Length (cm)
87
(n = 59): 79.7% (47) had no visible abnormalities, 11.9% (7) had propeller-like wounds,
and 5.1% (3) showed evidence of fisheries interactions.
The cumulative prey curve for the Kemp’s ridley whole samples collected in
Virginia from 1991 to 2002 (n = 23) appears to reach an asymptote, suggesting that most
major prey items were encountered (Figure 39). Overall, whole Kemp’s ridley samples
had an average dry weight of 51.1 g (SD = 51.4 g, median = 33.2 g), and there were an
average of 12.3 prey items per whole sample (SD = 16.9, median = 7.0) and 6.3 large
prey items (horseshoe crab, crabs, fish, whelks, moon snails) (SD = 4.1, median = 6.0)
per whole sample. Linear regression indicated a positive relationship between Kemp’s
ridley SCL and total and large prey dry weights (Figure 40), but there was no significant
linear relationship between SCL and prey numbers (Figure 41).
Interannual diet
The cumulative prey curve for whole Kemp’s ridley samples collected in Virginia
during 2000-2002 (n = 18) appeared to be approaching an asymptote, but the 1991-1994
curve (n = 5) did because of the small number of samples (Figure 42). Due to these
sampling limitations, only general diet data (n = 59, 1983-2002) and %F data for all
samples (n = 33, 1987-2002) were examined with correspondence analysis.
General prey data was compiled from 59 Kemp’s ridleys examined during 1983 to
2002 and was divided into five different year groups (1983-1984, 1987-1989, 1991-1994,
1999-2000, and 2001-2002) (Figure 43a). Crustaceans were dominant throughout the
ridley data set. The rare occurrence of horseshoe crabs and fish may be an artifact of
88
FIGURE 39. Cumulative prey curve for whole Kemp’s ridley samples collected in
Virginia during 1991 to 1994 and 2000 to 2002 (n = 23). Samples were randomized
ten times and numbers of prey types averaged. Error bars represent ± one standard
deviation.
Cumulative Number of Prey Types
35
30
25
20
15
10
5
0
0
5
10
15
Cumulative Number of Samples
20
25
89
FIGURE 40. Linear regressions of Kemp’s ridley straight carapace length (SCL)
versus (a) total dry weight of Virginia whole samples and (b) dry weights of large
prey items (horseshoe crab, crustaceans, fish, Atlantic moon snail) in Virginia whole
samples (n = 23).
Y = -109.951 + 4.44451X
(a)
R-Sq = 40.9 %
ANOVA: p = 0.001
Total Dry
Lk DryWeight
Wt
(g)
200
100
0
20
30
40
50
Lk SCL (cm)
SCL (cm)
(b)
Large Prey
Lk LPDry
Dry Wt
Weight (g)
Y = -106.254 + 4.28814X
R-Sq = 37.3 %
ANOVA: p = 0.002
200
100
0
20
30
40
Lk SCL (cm)
SCL (cm)
50
90
FIGURE 41. Linear regressions of Kemp’s ridley straight carapace length (SCL)
versus (a) total number of prey items in Virginia whole samples and (b) total number
of large prey items (horseshoe crab, crustaceans, fish, Atlantic moon snail) in
Virginia whole samples (n = 23). Note: neither of these regressions is significant.
Y = 1.48853 + 0.293551X
(a)
R-Sq = 1.6 %
ANOVA: p = 0.564
90
Lk Numbers
Number
of Prey
80
70
60
50
40
30
20
10
0
20
30
40
50
Lk SCL (cm)
SCL (cm)
Y = 2.02812 + 0.117714X
(b)
R-Sq = 4.5 %
ANOVA: p = 0.333
Lk of
LP Number
Number
Large Prey
20
10
0
20
30
40
Lk SCL (cm)
SCL (cm)
50
91
FIGURE 42. Cumulative prey curves for whole Kemp’s ridley samples collected in
Virginia during (a) 1991 to 1994 (n = 5) and (b) 2000 to 2002 (n = 18). Samples
were randomized ten times and numbers of prey types averaged. Error bars
represent ± one standard deviation.
Cumulative Number of Prey Types
(a)
35
30
25
20
15
10
5
0
0
5
10
15
20
25
20
25
Cumulative Number of Samples
Cumulative Number of Prey Types
(b) 35
30
25
20
15
10
5
0
0
5
10
15
Cumulative Number of Samples
92
FIGURE 43. Frequency of occurrence of (a) major prey groups in all Kemp’s ridley
diet data (n = 59) and (b) major prey items in all Kemp’s ridley samples (n = 33)
collected in Virginia during 1983 to 2002. Note: Due to incons istent sampling,
these time series are not continuous.
(a)
100
90
80
% Occurrence
70
60
50
40
30
20
10
0
Horseshoe crab
Crustacean
1983-1984 (n = 2)
1999-2000 (n = 13)
Mollusc
1987-1989 (n = 8)
2001-2002 (n = 26)
Fish
1991-1994 (n = 10)
(b)
100
90
80
60
50
40
30
20
1987-1989 (n = 6)
1991-1994 (n = 9)
2000-2002 (n = 18)
Atlantic moon
snail
Bony Fish
Lady crab
Purse crab
Rock Crab
Hermit crab spp.
Spider crab spp.
0
Callinectes spp.
10
Horseshoe crab
% Occurrence
70
93
small sample size, but neither has been reported previously in the literature as part of the
diet in Virginia (Bellmund et al. 1987; Keinath et al. 1987; Lutcavage and Musick 1985).
Additionally, the recent addition of fish to ridley diet would not be surprising given
trends observed in the loggerhead data. Correspondence analysis also suggests that
crustaceans remained a key component of Kemp’s ridley diet during the years examined
(Figure 44a).
More specific data were acquired for those Kemp’s ridleys that were sampled
(Tables 12-14). Target prey species appeared to include horseshoe crabs, decapod
crustaceans, fish, and moon snails. As with horseshoe crabs and fish, the appearance of
hermit crabs, purse crabs, and moon snails in the 2000-2002 diet data may be due to the
increased sampling effort (Figures 43b and 45). The disproportionate sampling may also
be the cause for the separation of the recent samples from the 1987-1989 and 1991-1994
samples in the CA biplot seen in Figure 44b. At best, it can be concluded that Callinectes
spp. (predominantly blue crabs) and Libinia spp. (spider crabs) were important
components of ridley diet in Virginia from 1987 to 2002.
Only three ridleys were examined that had consumed fish. One ridley from 2000
had consumed croaker, and two from 2002 had consumed both croaker and menhaden.
Due to small sample sizes, Kemp’s ridley data were not examined by size class, sex, or
season.
Interspecific Competition
The Schoener (1970) index was used to estimate diet overlap between loggerhead
and Kemp’s ridleys in Virginia during 2001 and 2002. Earlier years were not examined
94
FIGURE 44. Biplots of year division and prey type principal components (PCs) for
PC1 and PC2 of a correspondence analysis using (a) %F values of general diet
categories for all Kemp’s ridley data (n = 59) and (b) %F values of major prey items
from all Kemp’s ridley samples (n = 33) collected in Virginia during 1983 to 2002.
PC1 and PC2 account for 81.54% and 100.0% of the data in (a) and (b), respectively.
Number of samples is in parentheses.
(a)
Component 2
1.0
Horseshoe crab
0.5
Fish
Mollusc
01-02 (26)
87-89 (8)
91-94 (10)
99-00 (13)
0.0
Crustacean
-0.5
83-84 (2)
-0.5
0.0
0.5
1.0
Component 1
(b)
1
Horseshoe crab
Component 2
1987-1989 (6)
Spider Rock
crab spp.
crab
2000-2002 (18)
0
Callinectes spp.
Fish,
Hermit crab &
Hermit
Purse
Purse
Bony
crab
crab
crab
fishspp.
1991-1994 (9)
Lady crab
-1
-1
0
Component 1
1
TABLE 12: Frequency of occurrence of all prey items found in Kemp's ridley samples
(whole and partial) from Virginia during 1987 to 2002 (n = 33).
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Unidentified portunid
Rock crab
Spider crab spp.
Lady crab
Hermit crab spp.
Purse crab
Mantis shrimp
Other Crustaceans
Crab barnacle
Unidentified crustacean tissue
Fish
Bony fish
Molluscs
Bivalves
Eastern American oyster
Blue mussel
Unidentified bivalve
Gastropods
Cerith sp.
Wentletrap
Eastern mud snail
Three-line mud snail
Unidentified mud snail
Mottled dog whelk
Atlantic moon snail
Unidentified gastropod
Plants
Widgeon grass
Gulfweed sp.
Eelgrass
Unidentified marine plant
Unidentified terrestrial plant
19871989
(n=6)
19911994
(n=9)
20002002
(n=18)
Overall
(n = 33)
16.7
16.7
0.0
0.0
5.6
5.6
6.1
6.1
100.0
100.0
100.0
100.0
Callinectes sapidus
Callinectes sp.
Cancer irroratus
Libinia spp.
Ovalipes ocellatus
Pagurus spp.
Persephona mediterranea
Squilla empusa
83.3
100.0
72.2
81.8
16.7
0.0
5.6
6.1
16.7
11.1
27.8
21.2
50.0
33.3
66.7
54.5
0.0
11.1
5.6
6.1
0.0
0.0
33.3
18.2
0.0
0.0
44.4
24.2
0.0
0.0
5.6
3.0
Chelonibia patula
--
16.7
0.0
0.0
3.0
33.3
22.2
61.1
45.5
0.0
0.0
16.7
9.1
0.0
0.0
16.7
9.1
33.3
44.4
50.0
45.5
Limulus polyphemus
--
Crassostrea virginica
Mytilus edulis
-Bittium sp.
Epitonium sp.
Ilyanassa obsoleta
Ilyanassa trivittatus
Ilyanassa or Nassarius sp.
Nassarius vibex
Neverita duplicata
-Ruppia maritima
Sargassum sp.
Zostera marina
---
0.0
0.0
5.6
3.0
16.7
22.2
22.2
21.2
16.7
11.1
11.1
12.1
0.0
0.0
11.1
6.1
0.0
0.0
5.6
3.0
0.0
0.0
5.6
3.0
0.0
11.1
22.2
15.2
0.0
0.0
11.1
6.1
0.0
11.1
5.6
6.1
0.0
0.0
5.6
3.0
0.0
0.0
5.6
3.0
16.7
16.7
77.8
0.0
55.6
16.7
54.5
12.1
0.0
11.1
5.6
6.1
0.0
44.4
38.9
33.3
0.0
44.4
22.2
24.2
0.0
0.0
5.6
3.0
Miscellaneous
Rocks
Unidentified tissue
Anthropogenic Items
Hook and line gear
----
27.3
16.7
22.2
11.1
-5.6
-9.1
33.3
11.1
16.7
18.2
0.0
0.0
5.6
3.0
0.0
0.0
5.6
3.0
TABLE 13. Percent occurrence (%F), percent dry weight (%W), percent number (%N),
and percent index of relative importance (%IRI) of all prey items found in whole Kemp’s
ridley gut samples from Virginia during 1991 to 1994 (n = 5). Note: colonial animals
were given a count (number) of one.
Crustaceans
Decapods
Blue crab
Rock crab
Spider crab spp.
Lady crab
Other Crustaceans
Unidentified crustacean tissue
Molluscs
Bivalves
Blue mussel
Unidentified bivalve
Gastropods
Three-line mud snail
Plants
Eelgrass
Unidentified marine plant
Miscellaneous
Rocks
Unidentified tissue
%F
%W
%N
%IRI
100.0
85.7
32.4
68.3
100.0
20.0
40.0
20.0
29.5
7.0
14.5
0.3
20.6
2.9
5.9
2.9
65.6
2.6
10.7
0.9
40.0
80.0
34.3
0.9
-67.6
-31.7
Mytilus edulis
--
40.0
20.0
0.1
0.3
8.8
2.9
4.7
0.9
Ilyanassa trivittatus
20.0
100.0
60.0
80.0
20.0
20.0
20.0
0.4
0.4
0.2
0.3
13.0
0.0
12.9
55.9
-------
14.7
-------
Callinectes sapidus
Cancer irroratus
Libinia spp.
Ovalipes ocellatus
--
Zostera marina
----
TABLE 14. Percent occurrence (%F), percent dry weight (%W), percent number (%N),
and percent index of relative importance (%IRI) of all prey items found in whole Kemp’s
ridley gut samples from Virginia during 2000 to 2002 (n = 18). Note: colonial animals
were given a count (number) of one.
Chelicerates
Horseshoe crab
Crustaceans
Decapods
Blue crab
Unidentified portunid
Rock crab
Spider crab spp.
Lady crab
Hermit crab spp.
Purse crab
Mantis shrimp
Other Crustaceans
Unidentified crustacean tissue
Fish
Bony fish
Molluscs
Bivalves
Eastern American oyster
Blue mussel
Unidentified bivalve
Gastropods
Cerith sp.
Wentletrap
Eastern mud snail
Three-line mud snail
Unidentified mud snail
Mottled dog whelk
Atlantic moon snail
Unidentified gastropod
Plants
Widgeon grass
Gulfweed sp.
Eelgrass
Unidentified marine plant
Unidentified terrestrial plant
Miscellaneous
%F
%W
%N
%IRI
Limulus polyphemus
5.6
5.6
100.0
0.3
0.3
94.0
0.4
0.4
51.2
0.0
0.0
85.6
Callinectes sapidus
Callinectes sp.
Cancer irroratus
Libinia spp.
Ovalipes ocellatus
Pagurus spp.
Persephona mediterranea
Squilla empusa
72.2
5.6
27.8
66.7
5.6
33.3
44.4
5.6
21.7
0.1
0.8
40.1
0.1
0.2
7.1
0.0
16.1
4.4
3.2
12.9
0.8
3.6
9.7
0.4
34.6
0.3
1.4
44.7
0.1
1.6
9.5
0.0
61.1
16.7
16.7
50.0
23.7
3.0
3.0
0.7
-2.0
2.0
46.4
-0.5
1.1
13.9
Crassostrea virginica
Mytilus edulis
--
5.6
22.2
11.1
0.0
0.0
0.0
0.4
6.9
0.8
0.0
1.9
0.1
Bittium sp.
Epitonium sp.
Ilyanassa obsoleta
Ilyanassa trivittatus
Ilyanassa or Nassarius sp.
Nassarius vibex
Neverita duplicata
--
11.1
5.6
5.6
22.2
11.1
5.6
5.6
5.6
61.1
11.1
11.1
33.3
27.8
5.6
16.7
0.0
0.0
0.1
0.1
0.2
0.2
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
2.0
5.6
0.4
0.8
6.5
2.4
20.6
0.8
1.2
--------
0.8
0.0
0.1
1.8
0.4
1.5
0.1
0.1
--------
---
Ruppia maritima
Sargassum sp.
Zostera marina
---
Rocks
Unidentified tissue
Anthropogenic Items
Hook and line gear
----
5.6
16.7
5.6
5.6
0.0
2.0
-gear missing
-----
-----
100
FIGURE 45. (a) Frequency of occurrence, (b) percent dry weight, (c) percent
number, and (d) percent index of relative importance (IRI) in whole Kemp’s ridley
gut samples collected in Virginia from 1991 to 1994 and 2000 to 2002 (n = 23).
(a)
100
90
% Occurrence
80
70
60
50
40
30
20
Lady crab
Bony Fish
Atlantic moon
snail
Bony Fish
Atlantic moon
snail
Purse crab
Lady crab
1991-1994 (n = 5)
Rock Crab
Spider crab spp.
Callinectes spp.
Horseshoe crab
0
Hermit crab spp.
10
2000 - 2002 (n = 18)
(b)
70
60
40
30
20
1991-1994 (n = 5)
Purse crab
Rock Crab
Hermit crab spp.
Spider crab spp.
0
Callinectes spp.
10
Horseshoe crab
% Dry Weight
50
2000 - 2002 (n = 18)
1991-1994 (n = 5)
60
50
40
30
20
10
0
2000 - 2002 (n = 18)
Lady crab
Purse crab
Rock Crab
Hermit crab spp.
Spider crab spp.
Callinectes spp.
Atlantic moon
snail
70
Atlantic moon
snail
(d)
Bony Fish
2000 - 2002 (n = 18)
Bony Fish
Lady crab
1991-1994 (n = 5)
Purse crab
Rock Crab
Hermit crab spp.
Spider crab spp.
Callinectes spp.
Horseshoe crab
0
Horseshoe crab
% IRI
% Number
101
FIGURE 45 (Continued).
(c)
70
60
50
40
30
20
10
102
due to small numbers of ridley samples, and only whole samples were used in this
calculation. Average dry weight values were used in the calculations, and the prey items
included were horseshoe crabs, Callinectes spp., spider, hermit, rock, and purse crabs,
bony fish, whelks, and Atlantic moon snails, and. The overlap calculated for 2001 (23
loggerheads, 7 ridleys) was 33.4%, and the 2002 (22 loggerheads, 9 ridleys) overlap was
58.0%. Combining the two years gave an overlap value of 46.1% between the
loggerheads and Kemp’s ridleys examined.
DISCUSSION
Loggerheads
Interannual diet
The diet of loggerhead sea turtles in Virginia appears to have shifted from
horseshoe crab dominance during the early to mid-1980s to blue crab dominance in the
late 1980s and early 1990s, and then from a blue crab-dominated diet to a fish-dominated
diet by the mid-1990s and in 2001 to 2002. Additionally, spider crabs and rock crabs
became more prevalent in the diet during the 1990s, and hermit crabs (and their moon
snail shells) were observed more frequently in samples from 2001 and 2002. These diet
shifts are not surprising given the declines in horseshoe crab and blue crab abundance.
No estimates are available for the Chesapeake Bay horseshoe crab population in
any year (C. N. Shuster, pers. comm.) and records of horseshoe crab distribution and
abundance within the Bay are fragmentary and largely unpublished (Shuster 1985);
however, information can be gained from Virginia landings data (Figure 1). Reported
Virginia horseshoe crab landings within the Bay and its tributaries peaked in 1986 at
about 80,000 pounds (approximately 20,000 to 31,000 animals depending on average
weight), and they decreases to less than half of that in the next two years. Given that
horseshoe crabs require about ten years to mature (Berkson and Shuster 1999), these
diminished landings probably reflect a decrease in Chesapeake Bay, Virginia horseshoe
103
104
crab abundance. Continued fishing pressure in conjunction with this long time to
maturity likely diminished horseshoe crab numbers in the late 1980s and early 1990s,
possibly so much that loggerheads shifted their diets. Additionally, horseshoe crabs from
offshore areas may enter the Bay to spawn during May and June (Williams 1985; C. N.
Shuster, pers. comm.). As such, the explosion of the horseshoe crab bait fishery in the
late 1990s and the observed 50% population decline in the northwestern Atlantic
(Tanacredi 2001) undoubtedly affected spring and summer horseshoe crab numbers in the
Bay during more recent years.
Although the Virginia blue crab fishery remained intensive over the entire time
span of this study, the phase shift in blue crab abundance identified by Lipcius and
Stockhausen (2002) is a likely cause for the shift away from blue crab dominance in
loggerhead diet. The blue crab phase shift occurred around 1992, and loggerhead diet
had noticeably shifted by the mid-1990s. Blue crabs were infrequent in the diet by 20012002 and had a %IRI value of less than 3% during these years. The decreased
importance of blue crabs in the diet is likely because spawning stock, recruitment, female
size, and size at maturity values during 1992-2000 were all lower than those for 19851991 (Lipcius and Stockhausen 2002). The blue crab population was certainly
compromised further by the Virginia blue crab landings during 1993-2001, which were at
or near 1985-1991 levels (Figure 3).
The apparent severe declines in horseshoe crab and blue crab populations in the
Chesapeake Bay seem to have caused loggerheads to shift their diet to one dominated by
finfish. Sea turtles are not considered to be fast or agile enough to catch large quantities
of fish (Bellmund et al. 1987; Shoop and Ruckdeschel 1982). Aside from the occasional
105
benthic inhabitant, fish found in sea turtle gut contents are assumed to be acquired either
as discarded bycatch (Shaver 1991; Shoop and Ruckdeschel 1982; Tomas et al. 2001;
Youngkin and Wyneken, in press) or in nets (Bellmund et al. 1987). This dependence on
fisheries to provide food may put the turtles at more risk for boat strikes or entanglement
in nets.
Menhaden, croaker, seatrout (Cynoscion sp.), striped bass, and bluefish were the
fish species most frequently encountered in Virginia loggerhead samples (Table10), and
all are commercially important in Virginia’s gillnet and poundnet fisheries (Mansfield et
al. 2001, 2002a). The fish species composition and the fact that few turtles had
consumed both fish and scavenging mud snails (four in 2001 and two in 2002), suggests
that the turtles examined were feeding primarily on live and fresh dead fish from nets.
Sea turtles are known to enter the pound or “heart” of poundnets successfully and
unharmed, and VIMS has relied on poundnetters to provide live turtles since the turtle
program’s inception (Lutcavage 1981). Turtles are also at risk of becoming entangled
and drowning in poundnet leaders, particularly those with large mesh (greater than 12inch stretch) or stringers (Bellmund et al., 1987). One turtle that stranded in 2002 was
found entangled in a section of gillnet (Virginia stranding data), and its stomach
contained several squares of mesh in addition to bluefish, seatrout, and spot (Leiostomus
xanthurus). Although some turtles entangle in nets and drown (Bellmund et al. 1987;
Mansfield et al. 2002b), the presence of fish in the gut alone does not definitively
implicate a fishery-related death, and many of the fish encountered in this study were
comprised of disarticulated bones and tissue in later stages of digestion.
106
Size-specific diet
Examination of the whole loggerhead samples suggests that a partial diet shift
occurs after benthic immature stage animals reach maturity. The 40.0-69.9 cm SCL
loggerhead diet differs somewhat from the 70.0-99.9 cm SCL diet. The turtles in the
latter size class (n = 106) were probably all immature, whereas the majority of the turtles
in the second size class (n = 22) were likely to be mature adults (TEWG 1998; Van
Buskirk and Crowder 1994). The data suggest that as Virginia loggerheads mature, fish
become less prevalent in the diet, whereas horseshoe crabs and whelks become more
important; however, this conclusion is made hesitantly due to the small sample size for
larger loggerheads. This sampling limitation occurred because only about 5% of
loggerheads that enter Virginia waters are adults (Musick and Limpus 1997; Figure 13).
Loggerheads from Cumberland Island, Georgia sampled during 1979 to 1999 also
appeared to eat less fish as they increased in size, but the amount of crustaceans
consumed increased with size (Youngkin and Wyneken, in press).
Sex-specific diet
There appears to be little or no partitioning of food resources between the male
and female loggerheads examined. The same conclusion was reached in a comparison of
122 males and 217 females from Cumberland Island, Georgia (Youngkin and Wyneken,
in press).
107
Interseasonal diet
Spring and summer loggerhead diet differed somewhat from fall diet with regards
to fish and horseshoe crab consumption and the species of crustaceans consumed, but the
sample size for the fall was only 14, compared to 47 for spring and 64 for summer. The
smaller sample size for fall months may have skewed the results. Youngkin and
Wyneken (in press) did not find any seasonal effects on the consumption of crustaceans
or fish by loggerheads stranding on Cumberland Island, but consumption of moon snails
and whelks increased significantly from spring (n = 105) to summer (n = 214) to fall (n =
48).
Kemp’s Ridleys
All of the Kemp’s ridleys examined were in the benthic immature size class, and
the majority of samples were collected during 2000 to 2002; however, it is clear that blue
crabs and spider crabs were key components of Virginia ridley diet from 1987 to 2002.
In comparison, the smaller Kemp’s ridleys found in New York appear to concentrate their
foraging efforts on slower-moving types of crabs, including spider crabs and rock crabs
(Burke et al. 1993; Burke et al. 1994; Morreale and Standora 1991). Ridleys from
Georgia (Frick and Mason 1998) and Texas (Shaver 1991) appear to consume a large
amount of blue crabs and other portunid (swimming) crabs, in addition to the slower,
walking crabs. Both the turtle size range and prey composition of the Virginia samples
are more similar to the ridleys examined in Georgia and Texas than to those from New
York. The appearance of hermit crabs, purse crabs, and fish in the Virginia 2000-2002
samples could be due to the small sample sizes in earlier years, or it may suggest that
108
Chesapeake Bay blue crab declines (Lipcius and Stockhausen 2002) are beginning to
affect ridley diet.
Interspecific Competition
Sample sizes were only sufficient for 2001 and 2002 to compare the diet of
Virginia loggerheads and Kemp’s ridleys. The overlap for major prey items in 2001 was
33.4%, while the 2002 value was 58.0%. The discrepancy between the years is due in
part to items that were found in 2002 samples but not in 2001 samples: purse and rock
crabs for the loggerheads and horseshoe crabs and fish for the ridleys. The overlap for
the two years combined (46.1%) may be a better estimation of the overlap between
loggerhead and ridley diet in recent years. The actual foraging range overlap may be
minimal, as telemetry data suggest that loggerheads forage in deeper waters than ridleys
(Byles 1988; Keinath et al. 1987).
Concluding Remarks
In addition to establishing a baseline for the current diet of both loggerheads and
Kemp’s ridleys in Virginia, this long-term diet study suggests two shifts in loggerhead
diet that were likely due to fishery-induced prey declines. In general, Virginia’s
loggerheads and Kemp’s ridleys are benthic carnivores, but loggerheads appear to have
become more opportunistic in response to prey declines. In order to better understand the
effects of the horseshoe crab and blue crab fisheries on turtle diet, as well as to
investigate potential interactions between turtles and finfish fisheries, turtle gut contents
should continue to be monitored. At the very least, necropsies should be conducted on
109
strandings whenever possible, and the contents of the entire digestive tract examined and
recorded. Such information may be useful in the management of various fisheries in
Virginia, as well as in conservation schemes for these two protected sea turtle species.
APPENDIX I. Contents of loggerhead samples from Maryland (n = 10) and
North Carolina (n = 6).
Marine turtle (MT) numbers are expressed as "MT-year-month-day-turtle number
by day". Letters after horseshoe crabs and blue crabs indicate sex of animals:
F (female), M (male), U (unknown).
Turtle: MT-84-10-17-02 (VIMS Tags: G1055, G1056, K4004, K4005)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces
SCIENTIFIC NAME
CALLINECTES SAPIDUS
LIMULUS POLYPHEMUS
--
COMMON NAME
BLUE CRAB (U)
HORSESHOE CRAB (U)
ROCKS
#
3
1
--
WET WT (g)
37.7
26.7
0.3
DRY WT (g)
14.5
8.7
0.1
#
2
1
-2
-2
1
1
1
WET WT (g)
453.9
114.5
14.7
10.9
26.3
15.2
0.8
1.4
0.1
DRY WT (g)
142.3
39.4
14.2
7.8
4.4
3.5
0.4
0.2
0.1
#
3
1
1
WET WT (g)
270.5
7.4
0.5
DRY WT (g)
100.6
3.9
0.2
#
5
1
1
--
WET WT (g)
296.8
180.5
0.2
0.1
DRY WT (g)
76.0
47.0
0.1
0.1
Turtle: MT-87-06-11-01 (VIMS Tags: G1064, G1065)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces (2 samples)
SCIENTIFIC NAME
LIMULUS POLYPHEMUS
CANCER IRRORATUS
-GEUKENSIA DEMISSUS
-CALLINECTES SAPIDUS
--MYTILUS EDULIS
COMMON NAME
HORSESHOE CRAB (2 M)
ROCK CRAB
ROCKS
RIBBED MUSSEL
UNIDENTIFIABLE TISSUE
BLUE CRAB (U)
UNIDENTIFIED BIVALVE
UNIDENTIFIED HERMIT CRAB
BLUE MUSSEL
Turtle: MT-87-06-29-02 (VIMS Tags: K6431, K6432)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces (2 samples)
SCIENTIFIC NAME
CALLINECTES SAPIDUS
BREVOORTIA TYRANNUS
LIMULUS POLYPHEMUS
COMMON NAME
BLUE CRAB (1M, 2 MATURE F)
MENHADEN
HORSESHOE CRAB (U)
Turtle: MT-87-06-29-06 (VIMS Tags: K4568, K4569, PPN149)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces (2 samples)
SCIENTIFIC NAME
CALLINECTES SAPIDUS
LIMULUS POLYPHEMUS
MYTILUS EDULIS
--
COMMON NAME
BLUE CRAB (U)
HORSESHOE CRAB (F)
BLUE MUSSEL
UNIDENTIFIED MARINE PLANT
Turtle: MT-87-07-17-03 (VIMS Tags: PPN143, PPN144)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces
SCIENTIFIC NAME
-CALLINECTES SAPIDUS
--TELLINA SP.
--
COMMON NAME
ROCKS
BLUE CRAB (U)
UNIDENTIFIED BONY FISH
UNIDENTIFIED BIVALVE
TELLIN SP.
UNIDENTIFIED MARINE PLANT
#
-1
1
1
1
--
WET WT (g)
27.8
41.6
3.9
0.8
0.1
0.2
DRY WT (g)
27.1
11.9
1.4
0.4
0.1
0.1
Turtle: MT-90-05-25-08 (VIMS Tags: QQB422, QQB424, QQB499, QQB500)
Location: Mouth of Potomac River, MD (Western Bay)
Sample Type: Whole Tract
SCIENTIFIC NAME
UNKNOWN
CALLINECTES SAPIDUS
NASSARIUS VIBEX
----ZOSTERA MARINA
COMMON NAME
BONY FISH
BLUE CRAB (U)
MOTTLED DOG WHELK
UNIDENTIFIED MARINE PLANT
UNIDENTIFIED LEAVES
UNIDENTIFIED BIVALVES
ROCK
EELGRASS
#
8
1
4
--8
---
WET WT (g)
192.5
16.2
2.7
1.6
0.2
0.2
0.2
0.1
DRY WT (g)
58.9
4.0
1.8
0.1
0.1
0.1
0.1
0.1
#
-1
1
2
9
3
3
1
1
4
3
--1
WET WT (g)
208.7
147.5
41.7
29.1
28.3
9.9
5.5
1.5
0.5
0.5
0.3
0.2
0.2
0.3
DRY WT (g)
78.5
43.1
18.5
15.4
10.5
5.4
2.1
1.3
0.4
0.4
0.3
0.1
0.1
0.1
Turtle: MT-90-12-09-01
Location: Hatteras, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
COMMON NAME
-UNIDENTIFIABLE CRUSTACEAN TISSUE
PARALICHTHYS DENTATUS
SUMMER FLOUNDER
LIBINIA EMARGINATA
NINE-SPINED SPIDER CRAB
PERSEPHONA MEDITERRANEA
PURSE CRAB
OVALIPES OCELLATUS
LADY CRAB
CALLINECTES SAPIDUS
BLUE CRAB (U)
PAGURUS POLLICARIS
BROAD-CLAWED HERMIT CRAB
NEVERITA DUPLICATA
ATLANTIC MOON SNAIL
-UNIDENTIFIED GASTROPOD
CHELONIBIA PATULA
CRAB BARNACLE
BALANUS SP.
ACORN BARNACLE
ZOSTERA MARINA
EELGRASS
-ROCKS
-UNIDENTIFIED BIVALVE
Turtle: MT-91-05-30-01 (VIMS Tags: QQB478, QQB479, QQB374, QQB375)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces
SCIENTIFIC NAME
LIMULUS POLYPHEMUS
COMMON NAME
HORSESHOE CRAB (U)
#
1
WET WT (g)
30.5
DRY WT (g)
14.3
Turtle: MT-91-12-02-01
Location: Flounder Trawler, 30 miles offshore of Oregon Inlet, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
-PAGURUS POLLICARIS
NEVERITA DUPLICATA
CALLINECTES SP.
ASABELLIDES OCULATA
ILYANASSA TRIVITTATUS
---
COMMON NAME
UNIDENTIFIED BIVALVES
BROAD-CLAWED HERMIT CRAB
ATLANTIC MOON SNAIL
UNIDENTIFIABLE PORTUNID CRAB
SOFT WORM TUBE
THREE-LINE MUD SNAIL
UNIDENTIFIED TERRESTRIAL LEAF
ROCK
#
4
5
1
1
1
1
---
WET WT (g)
3.1
7.3
2.5
3.4
0.7
0.4
0.1
0.1
DRY WT (g)
3.0
2.4
2.4
1.7
0.5
0.4
0.1
0.1
#
9
-1
4
1
1
1
-1
2
-1
-1
---1
1
WET WT (g)
17.5
32.0
7.5
6.6
9.5
5.1
3.2
2.4
0.9
0.7
0.8
2.0
2.1
0.5
0.4
1.4
0.2
0.1
0.1
DRY WT (g)
15.0
13.9
6.3
5.7
4.1
3.0
2.9
2.3
0.7
0.6
0.4
0.3
0.2
0.2
0.1
0.1
0.1
0.1
0.1
#
1
-1
2
--
WET WT (g)
3.4
4.1
0.3
0.1
0.1
DRY WT (g)
0.8
0.5
0.2
0.1
0.1
Turtle: MT-91-12-09-02
Location: Flounder Trawler, off Frisco, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
--CRASSOTREA VIRGINICA
ARGOPECTEN SP.
OVALIPES OCELLATUS
ECHINARACHNIUS PARMA
MERCENARIA MERCENARIA
-CREPIDULA SP.
OLIVELLA SP.
-PAGURUS POLLICARIS
SARGASSUM SP.
ASABELLIDES OCULATA
-ZOSTERA MARINA
-ANADARA SP.
--
COMMON NAME
UNIDENTIFIED BIVALVES
UNIDENTIFIABLE TISSUE
OYSTER
SCALLOPS
LADY CRAB
SAND DOLLAR
HARD CLAM
ROCKS
SLIPPER SHELL SP.
OLIVE SHELL
ALUMINUM
BROAD-CLAWED HERMIT CRAB
GULFWEED
SOFT WORM TUBE
PLASTIC
EELGRASS
UNIDENTIFIED MARINE PLANT
ARK SP.
UNIDENTIFIED GASTROPOD
Turtle: MT-91-12-10-01
Location: Flounder Trawler, off Hatteras Inlet, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
ASABELLIDES OCULATA
-NEVERITA DUPLICATA
-ZOSTERA MARINA
COMMON NAME
SOFT WORM TUBE
UNIDENTIFIABLE TISSUE
ATLANTIC MOON SNAIL
UNIDENTIFIED BIVALVES
EELGRASS
Turtle: MT-91-12-18-01
Location: Hatteras, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
-BUSYCON SP.
-ARGOPECTEN SP.
SARGASSUM SP.
ZOSTERA MARINA
--
COMMON NAME
UNIDENTIFIABLE TISSUE
17 EGG CASES (CONNECTED)
UNIDENTIFIED BIVALVES
SCALLOP
GULFWEED
EELGRASS
UNIDENTIFIED MARINE PLANT
#
-1
2
1
----
WET WT (g)
13.1
21.8
0.8
0.3
1.1
0.1
0.1
DRY WT (g)
3.5
2.8
0.5
0.3
0.1
0.1
0.1
#
WET WT (g)
3.9
0.1
DRY WT (g)
0.8
0.1
#
2
--
WET WT (g)
165.3
0.5
DRY WT (g)
66.8
0.1
Turtle: MT-92-01-20-01
Location: Flounder Trawler, offshore of NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
---
COMMON NAME
UNIDENTIFIABLE TISSUE
ROCK
Turtle: MT-94-05-31-01 (VIMS Tags: QQM791, PPX807, PPX808, PPX816)
Location: Solomon's Island, MD (Western Bay)
Sample Type: Whole Tract
SCIENTIFIC NAME
CYNOSCION SP.
--
COMMON NAME
STRIPED BASS, SEATROUT SP.
UNIDENTIFIED MARINE PLANT
Turtle: MT-02-06-11-07 (VIMS Tags: SSB919, SSV642)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces
SCIENTIFIC NAME
LIMULUS POLYPHEMUS
COMMON NAME
HORSESHOE CRAB (M)
#
1
WET WT (g)
88.8
DRY WT (g)
25.5
CALLINECTES SAPIDUS
ZOSTERA MARINA
BLUE CRAB (U)
EELGRASS
1
--
6.3
0.2
1.4
0.1
Turtle: MT-02-06-18-01 (VIMS Tags: XXF771, XXF772)
Location: Poundnet, Potomac River Mouth, MD (Western Bay)
Sample Type: Feces
SCIENTIFIC NAME
COMMON NAME
#
WET WT (g)
DRY WT (g)
BALANUS SP.
BREVOORTIA TYRANNUS ,
UNKNOWN
ACORN BARNACLE
2 MENHADEN, 1 UNIDENTIFIED
BONY FISH
15
48.1
38.2
3
29.2
10.9
--
WOOD
--
1.5
0.4
--
UNIDENTIFIED MARINE PLANT
--
0.1
0.1
--
PLASTIC
--
0.1
0.1
APPENDIX II. Contents of Kemp's ridleys samples from North Carolina
(n = 2).
Marine turtle (MT) numbers are expressed as "MT-year-month-day-turtle number
by day". Letters after horseshoe crabs and blue crabs indicate sex of animals:
F (female), M (male), U (unknown).
Turtle: MT-90-12-09-02
Location: Frisco, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
-LIBINIA DUBIA
CALLINECTES SP.
---ZOSTERA MARINA
COMMON NAME
UNIDENTIFIABLE CRUSTACEAN TISSUE
SIX-SPINED SPIDER CRAB
SWIMMING CRAB
UNIDENTIFIED BIVALVES
UNIDENTIFIED GASTROPOD
ROCKS
EELGRASS
#
-1
1
4
1
---
WET WT (g)
19.4
9.5
2.8
0.5
0.1
0.2
0.3
DRY WT (g)
5.8
3.0
1.2
0.4
0.1
0.1
0.1
#
1
2
-----
WET WT (g)
13.3
8.4
8.7
0.8
0.2
0.1
DRY WT (g)
8.3
5.1
3.0
0.1
0.1
0.1
Turtle: MT-91-12-09-01
Location: Flounder Trawler, off Frisco, NC (Outer Banks)
Sample Type: Whole Tract
SCIENTIFIC NAME
HEPATUS EPHELITICUS
OVALIPES OCELLATUS
-ZOSTERA MARINA
---
COMMON NAME
DOLLY VARDEN/CALICO CRAB
LADY CRAB
UNIDENTIFIABLE CRUSTACEAN TISSUE
EELGRASS
ROCKS
UNIDENTIFIED MARINE PLANT
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Lippson, A. J. and R. L. Lippson. 1997. Life in the Chesapeake Bay, Second Edition.
Johns Hopkins University Press, Baltimore, 294 pp.
Murdy, E. O., R. S. Birdsong, and J. A. Musick. 1997. Fishes of Chesapeake Bay.
Smithsonian Institution Press, Washington, D.C., 324 pp.
Williams, A. B. 1984. Shrimps, Lobsters, and Crabs of the Atlantic Coast of the Eastern
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VITA
Erin E. Seney
Born in Lexington, Kentucky on October 1, 1978. Graduated from Homer L. Ferguson
High School in Newport News, Virginia in June 1996. Earned Bachelor of Arts in
Biology, with a minor in Environmental Sciences, from the University of Virginia in May
2000. Entered Master of Science program at the College of William and Mary, School of
Marine Science in August 2000.
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