ASSESSMENT OF ARTIFICIAL REEF DISTRIBUTION PATTERN
INFLUENCES ON RELATIVE ABUNDANCE OF JUVENILE
RED SNAPPER ALONG THE MISSISSIPPI
GULF COAST
Final Project Report
1 August 2007 – 1 May 2010
Jason R. Brandt and Donald C. Jackson1
Department of Wildlife and Fisheries
Mississippi State University
Box 9690
Mississippi State, MS 39762
1
Principal investigator and to whom correspondence should be sent.
ACKNOWLEDGEMENTS
I would like to extend a heartfelt thanks to all of the individuals who helped
with my research and thesis. First and foremost, to my major advisor Dr. Donald C.
Jackson, thank you for this amazing opportunity and the support you have provided
throughout my time here. Thank you to my thesis committee members Dr. Leandro
(Steve) E. Miranda and Dr. Eric D. Dibble for your guidance and input during the
thesis preparation and writing process. Thanks is given to the Department of
Wildlife, Fisheries and Aquaculture for all of the logistical support, and to all of the
department faculty and staff who helped me along the way. Special appreciation is
extended to Kerwin Cuevas, Jimmy Sanders, Erik Broussard, Brandon Hall and all
other members of the Mississippi Department of Marine Resources (MSDMR) who
accompanied me out on the water and assisted me in the office. You all made me feel
welcome, and I truly could not have accomplished my research without your help.
Finally, thank you to the charter boat captains Tom Becker, Jay Trochesset, and
Kenny Barhanovich for providing the use of your boats to access and sample my
study site and relating invaluable personal experiences to aid in my study.
ii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................................ ii
LIST OF TABLES ...............................................................................................................v
LIST OF FIGURES .......................................................................................................... vii
CHAPTER
1. INTRODUCTION ...................................................................................................1
2. METHODS ..............................................................................................................7
Study Site .................................................................................................................7
Study Design ............................................................................................................8
Data Analysis .........................................................................................................11
Catch per Unit of Effort (CPUE) ....................................................................11
Mean Length ...................................................................................................13
Species Diversity ............................................................................................13
Growth ............................................................................................................14
Environmental Variables ................................................................................14
3. RESULTS ..............................................................................................................16
Sampling ................................................................................................................16
Catch Composition.................................................................................................16
Catch per Unit of Effort (CPUE) ...........................................................................16
Mean Length ..........................................................................................................18
Species Diversity ...................................................................................................19
Tag Return .............................................................................................................19
Growth ...................................................................................................................20
Environmental Variables .......................................................................................20
Post-Capture Condition..........................................................................................21
4. DISCUSSION........................................................................................................22
Catch per Unit of Effort (CPUE) ...........................................................................23
Mean Length ..........................................................................................................26
iii
Species Diversity ...................................................................................................28
Growth ...................................................................................................................28
Tag Return .............................................................................................................29
Environmental Variables .......................................................................................31
Post-Capture Condition..........................................................................................31
Conclusions ............................................................................................................32
Reef Balls versus Pyramids ...................................................................................34
LITERATURE CITED ......................................................................................................37
APPENDIX
A. TOTAL NUMBER OF FISH BY SPECIES COLLECTED WITH
TRAP NETS FROM SEPTEMBER 2007 THROUGH NOVEMBER
2008 AT EACH ARTIFICIAL REFF PATTERN WITHIN EACH
SECTION OF ARTIFICIAL REEF SITE FH-13 LOCATED
OFFSHORE OF MISSISSIPPI IN THE GULF OF MEXICO .........................63
iv
LIST OF TABLES
1. Latitudinal and longitudinal coordinates for the sections of artificial
reef site FH-13 located offshore of Mississippi in the Gulf of
Mexico and sampled during the period of September 2007
through November 2008 ....................................................................................44
2. Latitudinal and longitudinal coordinates for each artificial reef pattern
and total visits to each section and artificial reef pattern in artificial
reef site FH-13 located offshore of Mississippi in the Gulf of
Mexico and sampled during the period of September 2007 through
November 2008 .................................................................................................45
3. Number of total visits to each pattern and total number of pattern visits
by season at artificial reef site FH-13 located offshore of Mississippi
in the Gulf of Mexico and sampled during the period of September
2007 through November 2008 ...........................................................................46
4. Catch per unit effort (CPUE, red snapper/trap soak hour) of red snapper
for each trip to individual artificial reef patterns in Section A of
artificial reef site FH-13 located offshore of Mississippi in the Gulf
of Mexico and sampled during the period of September 2007
through November 2008 ....................................................................................47
5. Catch per unit effort (CPUE, red snapper/trap soak hour) of red snapper
for each trip to individual artificial reef patterns in Section B of
artificial reef site FH-13 located offshore of Mississippi in the Gulf
of Mexico and sampled during the period of September 2007
through November 2008 ....................................................................................48
6. Catch per unit effort (CPUE, red snapper/trap soak hour) of red snapper
for each trip to individual artificial reef patterns in Section C of
artificial reef site FH-13 located offshore of Mississippi in the Gulf
of Mexico and sampled during the period of September 2007
through November 2008 ....................................................................................49
7. Recapture data for red snapper captured with trap nets during
sampling from September 2007 through November 2008 at artificial
reef site FH-13 off the coast of Mississippi in the Gulf of Mexico...................50
v
8. Condition and location of capture of red snapper which were released
in any condition other than the best possible (Good) after being
captured with trap nets from September 2007 through November
2008 at artificial reef site FH-13 off the coast of Mississippi in
the Gulf of Mexico ............................................................................................51
vi
LIST OF FIGURES
1. Location of artificial reef site FH-13 in the northern Gulf of Mexico .....................53
2. Pyramid structures used to construct artificial reef complexes at
artificial reef site FH-13 in the northern Gulf of Mexico (2a) and
a trap that was used for collecting fish during sampling (2b)
(Photographs provided by the Mississippi Department of Marine
Resources) .........................................................................................................54
3. Artificial reef patterns deployed within each section of artificial reef
site FH-13 off the coast of Mississippi in the Gulf of Mexico ..........................55
4. Mean catch per unit of effort (CPUE; red snapper/trap soak-hour) by
pattern with associated standard error bars for red snapper captured
with trap nets during September 2007 through November 2008 from
artificial reef site FH-13 off the coast of Mississippi in the Gulf of
Mexico. The clump pattern consists of five closely spaced
pyramid structures, and the outlier patterns consist of five closely
spaced pyramids and two sets of two outlier pyramids at
100 ft (OL100), 200 ft (OL200), and 300 ft (OL300) from the main
clump of pyramids .............................................................................................56
5. Mean catch per unit of effort (CPUE; red snapper/trap soak-hour) by
season with associated standard error bars for red snapper captured
with trap nets during September 2007 through November 2008
from artificial reef site FH-13 off the coast of Mississippi in the
Gulf of Mexico. Seasons in which sampling took place were
spring (March, April, and May), summer (June, July, and August)
and fall (September, October, and November)..................................................57
6. Mean total length (mm) by pattern with associated standard error bars for
red snapper captured with trap nets during September 2007 through
November 2008 from artificial reef site FH-13 off the coast of
Mississippi in the Gulf of Mexico. The clump pattern consists of
five closely spaced pyramid structures, and the outlier patterns consist
of five closely spaced pyramids and two sets of two outlier pyramids
at 100 ft (OL100), 200 ft (OL200), and 300 ft (OL300) from the main
clump of pyramids .............................................................................................58
vii
7. Mean total length (mm) by season with associated standard error bars for
red snapper captured with trap nets during September 2007 through
November 2008 from artificial reef site FH-13 off the coast of
Mississippi in the Gulf of Mexico. Seasons in which sampling took
place were spring (March, April, and May), summer (June, July, and
August) and fall (September, October, and November) ....................................59
8. Red snapper length frequency distributions by reef pattern type. Length
measurements are total lengths (mm). Red snapper were captured
with trap nets during September 2007 through November 2008
from artificial reef site FH-13 off the coast of Mississippi in the
Gulf of Mexico. The clump pattern consists of five closely
spaced pyramid structures, and the outlier patterns consist of five
closely spaced pyramids and two sets of two outlier pyramids at
100 ft (OL100), 200 ft (OL200), and 300 ft (OL300) from the main
clump of pyramids .............................................................................................60
9. Red snapper length frequency distributions by season. Length
measurements are total lengths (mm). Red snapper were captured
with trap nets during September 2007 through November 2008 from
artificial reef site FH-13 off the coast of Mississippi in the Gulf of
Mexico. Seasons in which sampling took place were spring
(March, April, and May), summer (June, July, and August) and fall
(September, October, and November) ...............................................................61
10. Relationship between red snapper catch per unit of effort (CPUE; red
snapper/trap soak-hour) and environmental variables
(dissolved oxygen, salinity, and temperature) in the Mississippi
artificial reef site FH-13, Gulf of Mexico, from September 2007
through November 2008 ....................................................................................62
viii
CHAPTER 1
INTRODUCTION
Red snapper, Lutjanus campechanus, are long-lived, bottom dwelling,
predatory fish, capable of reaching large size, that range from Cape Hatteras, North
Carolina, across the continental shelf in the Gulf of Mexico, to the Yucatan Peninsula
(Patterson et al. 2001a). They support economically important recreational and
commercial fisheries in the northern Gulf of Mexico (Collins et al. 1980; Allman et
al. 2002, Franks et al. 2004) with an estimated annual value of $40 million (Rummer
2007). More than 95% of the total U.S. red snapper landings occur in the Gulf of
Mexico (Gillet et al. 2001).
Red snapper abundance has decreased by almost 90% in the northern Gulf of
Mexico in the past two decades, and they are considered a highly over-exploited
marine fish (Mitchell et al. 2004; Saillant and Gold 2006). In an effort to rebuild red
snapper stocks, the National Marine Fisheries Service (NMFS) and the Gulf of
Mexico Fishery Management Council (GMFMC) have undertaken a series of
regulatory efforts aimed at restricting the direct harvest of adult red snapper and the
indirect harvest of juveniles. Regulations for red snapper were first implemented by
the GMFMC in November 1984 under the Reef Fishery Management Plan (RFMP)
which stipulated a total allowable catch (TAC) and minimum size limits for the
recreational and commercial sectors (Gillig et al. 2001; Garber et al. 2004). In
1
August 2000, the minimum recreational length for red snapper was increased from 15
to 16 inches total length (TL), but even with stringent regulations, the red snapper
stock is still over-fished (SEDAR 2005), and the fishery has experienced major catch
fluctuations as well as declines from historic fishery landings (Garber et al. 2004).
Continued declines in red snapper stocks may be linked directly to high
juvenile bycatch mortality in the shrimp trawl fishery, and controlling the mortality
caused by the bycatch from the shrimp fishery is viewed as one of the most important
factors in the recovery of red snapper stocks (Gillig et al. 2001; Peabody 2004;
Saillant and Gold 2006; McDonough 2009). Parsons and Foster (2007) state that
90% of fishing mortality of juvenile (age-0 and age-1) red snapper comes from
shrimp trawl bycatch, and Gallaway et al. (2007) found that juvenile red snapper
enter the shrimp trawl fishery at 50 mm total length (TL) but do not appear to be fully
vulnerable to the shrimp trawls until they are 100 mm TL or longer (Gallaway et al.
1999).
Under the 1984 RFMP, bycatch reduction devices (BRDs) were required on
Gulf of Mexico shrimp trawls with the hope of reducing juvenile red snapper bycatch
mortality by up to 60%, which if accomplished would allow red snapper stocks to
rebuild to sustainable levels (Gazey et al. 2008). Gallaway and Cole (1999),
however, found that conditional survival of juvenile red snapper bycatch from trawls
equipped with BRDs was around 12%, and Wells (2007) stated that juvenile red
snapper excluded from trawls equipped with BRDs experience low survival due to
increased predation by larger fish and marine mammals, physiological stress, and
habitat displacement.
2
The bottom substrate of the continental shelf waters of the northern Gulf of
Mexico consists mostly of sand and mud with little to no vertical relief, which are
bottom traits conducive to shrimp trawling (Patterson and Cowan 2003; Wells and
Cowan 2007). Though juvenile red snapper spend most of their first year over those
sand and mud bottoms in the northern Gulf of Mexico, juvenile red snapper show
increasing preference for natural and artificial habitat with vertical relief. The
increasing preference for vertical structure may make artificial reefs important
components of red snapper stock rehabilitation by offering juvenile red snapper
which may be captured in shrimp trawls a place of preferred refuge off shrimping
grounds (McDonough 2009).
For the last 50 years, artificial reefs have been constructed and placed in the
Gulf of Mexico with the intention of enhancing recreational and commercial fishing
and rehabilitating depleted fish stocks. Artificial reef material has been placed off of
the Mississippi coast since the 1960’s, and today roughly 16,000 acres of designated
artificial reef sites can be found in the state’s offshore waters. Whereas substantial
research has been done on artificial reefs off of Alabama (Strelcheck et al. 2005;
Szedlmayer and Shipp 1994) and the oil rigs off Louisiana (Westmeyer et al. 2007;
McDonough 2009), relatively little research has been done on artificial reefs off the
coast of Mississippi and their possible roles in resource management (Lukens 1980;
Lukens et al. 1989).
Different aspects of artificial reef structure and placement must be taken into
account to elicit desired management results, and various studies have examined how
reef material, complexity, depth, isolation, density, height, and horizontal extension
3
relate to fish abundance and artificial reef success (Gregg 1995; Bohnsack and
Sutherland 1985; Strelcheck et al. 2005; Harrera et al. 2002). With a large number of
structural possibilities when choosing an artificial reef program, studies that look at
different artificial reef patterns, orientations, and structural characteristics, and how
they may influence each other, are necessary to elicit the best results for the
rehabilitation of red snapper stocks (Gregg 1995).
Reef spacing may be a particularly important consideration for artificial reef
managers. Various studies have explored the effects of reef spacing on fish
abundance (Bohnsack and Sutherland 1985; Sherman et al. 2002), with the intention
of determining how much space is necessary between artificial reef structures to
maximize benefits for desired fish species. For red snapper, the importance of reef
spacing may be directly linked to the Resource Mosaic Hypothesis, which in part
predicts that as reef spacing decreases, the access to soft-bottom prey around the reefs
also decreases (Frazer and Lindberg 1994).
Studies have shown that juvenile red snapper diets are largely composed of
non-reef associated soft-bottom prey such as shrimp and crabs found around natural
or artificial reef structures where the red snapper reside (McCawley and Cowan 2007;
Peabody 2004). Juveniles may create intense areas of prey depletion around the reef
structures (foraging haloes), with prey depletion increasing as reef spacing decreases
because of greater overlap of foraging activity (Lindberg et al. 1990; Frazer and
Lindberg 1994). The feeding haloes may have negative effects on abundance growth,
and residence time of juvenile red snapper on artificial reefs as they may be forced to
forage outside of the halo area making them more susceptible to predation (Lindberg
4
et al. 1990). Frazer and Lindberg (1994) believe that more widely spaced reefs
should result in decreased halo overlap which should lead to an increase in density of
potential soft-bottom prey species and red snapper foraging opportunities (Frazer and
Lindberg 1994). Because the resource mosaic hypothesis has possible consequences
for reef spacing, artificial reef managers need to understand whether the existence of
foraging haloes should inform their decisions on possible spacing and placement of
artificial reefs (McDonough 2009).
Understanding critical biological characteristics of red snapper such as early
life history requirements, growth rates, movements, pattern of settlement, and postsettlement site fidelity is important if they are to be the target species while dealing
with the development and management of artificial reef fisheries (Gregg 1995) and
answering the important question of whether or not artificial reefs aid in red snapper
production and possible stock rehabilitation. Geary et al. (2007) believe that
recruitment variability and year class strength of red snapper are likely determined
during early life, and identifying habitats or conditions that favor survival during the
nursery period is critical to management of red snapper. Larval red snapper spend
approximately 26 days in the planktonic stage prior to metamorphosis and first
appearance on benthic substrate (Szedlmayer and Lee 2004). Workman et al. (2002)
found that juvenile red snapper reef dependency occurs within their first year, with
age-0 and age-1 red snapper showing a preference for complex, high relief reef
structure.
Once recruited to structures, juvenile red snapper show high site fidelity and
quick growth. Diamond et al. (2007) found that 96% of tagged red snapper in their
5
study that were small [< 37.9 cm (TL)], and captured in shallow water (< 40 m),
stayed at their original tagging site. Juvenile red snapper take advantage of the
increased food source and protection from predation that artificial reefs provide,
allowing them to grow rapidly until they are about eight to ten years old (Wilson and
Nieland 2001; Fischer et al. 2004; Horst 2005).
These and other studies suggest that artificial reefs can play an important role
in the enhancement of red snapper stocks in the northern Gulf of Mexico because (1)
red snapper appear to recruit to artificial structures at an early age if the structures are
present, (2) juvenile red snapper show high site fidelity on artificial structures and (3)
once recruited to the structures, red snapper exhibit fast growth. Subsequently, and
with these perspectives in mind, I conducted a study to determine the influence of
placing artificial reef material in different patterns and the environmental parameters
associated with the artificial reefs on the recruitment of juvenile red snapper to those
structures in Mississippi coastal waters.
6
CHAPTER 2
METHODS
Study Site
The project area for this study was offshore artificial reef site Fish Haven-13
(FH-13), which is located approximately 40 kilometers (km) south of Pascagoula,
Mississippi in the northern Gulf of Mexico (Figure 1). The site encompassed an
approximate area of 38 km2 and ranged in depth from 20 to 26 meters (m). Artificial
reef site FH-13 was split into three sections A (18 km2), B (10 km2), and C (10 km2)
from north to south respectively across depth strata. Depth ranges for each section
were: Section A (20-24 m), Section B (24-26 m), and Section C (26-27 m).
Latitudinal and longitudinal coordinates for each section of FH-13 are given in Table
1. The bottom substrate of site FH-13 consisted mostly of sand and mud with little to
no vertical relief, which is consistent with most of the continental shelf waters of the
northern Gulf of Mexico (Patterson and Cowan 2003; Wells and Cowan 2007). Site
FH-13 was chosen for this study because of its large size, appropriate sampling depth
range, and the relatively small amount of other artificial reef material. This allowed
for the placement of artificial reefs in the desired patterns and intervals necessary for
the study to occur, with minimal influence from other structures.
7
Study Design
Fish sampling began in September 2007 and ended in November 2008. Prior
to sampling, pyramid shaped artificial reef structures with embedded stone
outcroppings were placed in different pre-determined patterns within Site FH-13
(between March 6 and June 6, 2007) (Figure 2a). The artificial reef structures were
composed of limestone and Coquina rock panels on cement frames. Each pyramid
had a 3.7 m triangle base and measured 2.4 m in height. Approximate weight of each
pyramid was 3.2 metric tons (mt).
Artificial reef complexes were deployed in separate, predetermined patterns
(treatments) within each section of FH-13 in a randomized complete block design;
and designated pyramid dispersion (clumped versus outlier spreads), and pyramid
placement intervals for horizontal positioning (30.5 m; 61.0 m; 91.4 m) from a central
clump in Site FH-13. For clumped dispersion, five closely spaced pyramids (all
vertically oriented) were used to constitute experimental units. Nine pyramids (all
vertically oriented) were used to constitute each experimental unit for the outlier
spread dispersion pattern. Within the outlier dispersion pattern, there were five
pyramids clumped in a core location, and two groups of two pyramids each
positioned equidistant at 30.5 m, 61.0 m, or 91.4 m from the core assemblage
location. The Mississippi Department of Marine Resources (MSDMR) chose outlier
distances in 100 feet (ft) increments (30.5 m=100 ft; 61.0 m=200 ft; 91.4 m=300 ft),
and reef patterns will be referred to using those predetermined outlier increment
numbers [clump, outlier 100 (OL100), outlier 200 (OL200), and outlier 300 (OL300)]
8
(Figure 3). One of each pattern (clump, OL100, OL200, and OL300) was located in
each separate section (A, B, and C) of FH-13 (Table 2).
Fish traps were used for fish collections. Traps were 0.97 m long, 0.67 m
wide, and 0.64 m high (Figure 2b). Funnel mouth size for each trap measured 175
mm by 115 mm, with the smaller mouth openings biased towards collection of
smaller, juvenile red snapper. Trap mesh size was 6.5 square centimeters (cm2). The
traps were collapsible for easy storage and transport. Culbertson and Peter (1998)
found that the use of traps reduced stress on captured fish and increased recapture
rates from 8.4% to 29.1% compared to sampling by hook and line.
Juvenile red snapper were collected to better understand the functional role of
artificial reefs in increasing the future numbers of spawning adults which will
ultimately aid in the rehabilitation of red snapper stocks. Szedlmayer and Lee (2004)
found that juvenile red snapper recruit to reef habitat during their first year at a
standard length (SL) of approximately 70 mm. Red snapper enter the recreational
fishery at 406 mm (TL). My study addressed pre-recruit red snapper [> 70 mm and <
406 mm (TL)].
Locations for sampling were determined by randomly selecting Section A, B,
or C. After the section was chosen, three artificial reef patterns within the section
were randomly selected. Four traps baited with cut bait (Gulf menhaden, Brevoortia
patronus) were set at each of the three artificial reef patterns and allowed to soak for
two hours (soak time was pre-determined by MSDMR from pre-sampling). Two
traps were dropped per pass over the reef site. All traps were set on the main clump
of five central pyramids.
9
Traps were pulled by hand. To avoid excessive fish handling, successive traps
were pulled only after all fish from the trap on deck were processed and back in the
water. Data on environmental characteristics [dissolved oxygen (DO)(milligrams per
liter; mg/L), salinity (parts per thousand; ppt), and water temperature (°C)] were
collected at the surface, mid depth, and bottom of the water column at sampling sites
using YSI 85 (YSI Incorporated, Yellow Springs, Ohio). If sample sites were within
0.8 km of one another, a reading was taken at a point between adjacent sampling
sites.
Additionally, depth (m), current direction, wind speed [kilometers/hour
(km/h)], and wave height (m) were recorded.
All fish collected in the traps were identified to species. For each collected
fish, total, fork, and standard lengths were recorded (mm). Absolute number data
collected for red snapper were used to determine catch per unit of effort (CPUE: red
snapper/ trap soak hour) and length frequency distributions. Gitschlag and Renaud
(1994) found that rapid retrieval of fish from depth may increase mortality due to
hyperbaric trauma leading to catastrophic decompression syndrome (CDS).
Subsequently, all fish collected during my sampling were vented using a hypodermic
needle venting tool.
Red snapper, gray triggerfish (Balistes capriscus), gag grouper (Mycteroperca
microlepis), and lane snapper (Lutjanus synagris) were tagged with gray FLOY®
(FLOY Tag and Manufacturing Incorporated, Seattle, Washington) t-bar anchor tags.
Each tag was individually-numbered and had a phone number that could be called to
report the capture of a tagged fish. Using a tagging gun, tags were inserted into the
musculature just below the dorsal fin. This has been found to be the best location to
10
minimize tag loss (Diamond et al. 2007). To address possible tag loss, recaptured
fish were tagged a second time with a second individually-numbered tag, but in the
case of a second recapture, the fish would not be tagged a third time (no fish would
have more than two individually numbered tags on it at a time). After tagging, fish
were released immediately back into the water and their condition was inferred.
Three condition categories were used: good (fish swam down vigorously after being
placed back in the water), fair (fish oriented itself correctly but didn’t swim down
immediately), and dead (fish was either dead or unresponsive once placed in the
water).
Data Analysis
Catch per Unit of Effort (CPUE)
The experimental design for this study represented a randomized complete
block design, with sections (A, B, and C) being the blocks and one of each reef
pattern (clump, OL100, OL200, and OL300) randomly placed within each block.
During sampling, however, only three of the four patterns in the chosen section were
sampled on a given trip. Thus, there was one missing value (un-sampled reef pattern)
for each trip. Due to the fact that I repeatedly visited the same reefs time after time,
repeated measures analysis was used, as estimates taken repeatedly on the same reefs
were most likely correlated. Traditional repeated measures ANOVA does not readily
allow data with missing values, however, so analysis was run using a repeated
measures mixed linear model (PROC MIXED, SAS Institute Inc., Cary N.C. 2008).
Days between tagging trips was the temporal repeated measure and patterns (nested
11
within sections) the subjects that were repeatedly sampled. The Kenward Rogers
degrees of freedom adjustment was used to properly determine degrees of freedom
for the analysis.
The model used directly assessed the effect of reef pattern and season
(independent variables) on CPUE (fish/hour; dependent variable) of red snapper.
Normal probability plots and Shapiro-Wilk values generated from PROC
UNIVARIATE (SAS Institute Inc., Cary N.C. 2008) were used to test the
assumptions of normality. The CPUE data were found to be significantly nonnormal, thus a natural log transformation of the CPUE data was performed to satisfy
the assumptions of normality. Sampling occurred during three seasons: spring
(March, April, and May), summer (June, July, and August), and fall (September,
October, and November). No sampling occurred in the winter months of December,
January, and February due to poor sampling conditions, so the winter season was not
considered for analysis. Section (block) was modeled as a random effect, with the
goal of making the findings of the study applicable outside of the study area. Several
co-variance structures were tested using restricted maximum likelihood (REML) and
Akaike’s information criterion corrected for sample size (AICc). Based on model
results, I used a spatial power (sp pow) covariance structure for the model. Model
parameter estimates were generated using REML, and an alpha level of 0.05 was used
for all analysis. In the case of significant results from the mixed model, least squares
analysis (LSMEANS, SAS Institute Inc., Cary N.C. 2008) was used for pair-wise
comparisons, with the significance level adjusted using the Bonferroni correction to
12
maintain the predetermined experimental error rate. Least squares mean CPUE and
standard error (SE) estimates were generated and back-transformed for reporting.
Mean Length
Mean total lengths (TL; mm) of red snapper were compared among different
reef patterns. Mean lengths were tested for normality using normal probability plots
and Shapiro-Wilk values generated from PROC UNIVARIATE (SAS Institute Inc.,
Cary N.C. 2008). The length data were significantly non-normal, and a square root
transformation was applied to normalize the data. Analysis was run using the same
repeated measures mixed linear model (PROC MIXED, SAS Institute Inc., Cary N.C.
2008) as used for CPUE analysis, and the model used directly assessed the effect of
reef pattern and season (independent variables) on red snapper mean TLs (dependent
variables). Parameter estimates were generated in the same manner as for the above
CPUE analysis, and least squares mean TL and standard error (SE) estimates were
generated and back-transformed for reporting. Length frequency distributions were
also developed for visual comparison analysis.
Species Diversity
Species diversity was calculated for each reef pattern on each trip to asses the
effect of species diversity on red snapper CPUE and TL. Species diversity was
calculated using the Shannon-Weiner Index:
S
H’= - ∑ pi ln pi
I=1
13
(1)
where S= the number of species in the sample and pi= the proportion of individual in
species I (ni/N). Species diversity data were tested for normality using normal
probability plots and Shapiro-Wilk values generated from PROC UNIVARIATE
(SAS Institute Inc., Cary N.C. 2008), and the data were found to follow a normal
distribution. Analysis was run using the same repeated measures mixed linear model
(PROC MIXED, SAS Institute Inc., Cary N.C. 2008) as used above. Models directly
assessed the effect of species diversity and species diversity*pattern interaction
(independent variables) on red snapper natural log transformed CPUE and square root
transformed TL (dependent variables).
Growth
Mark-recapture data were used to generate a growth estimate for red snapper.
Growth rate (mm/d) was estimated by dividing the change in TL by days at large for
each recaptured red snapper. An overall mean growth rate was determined by taking
the mean of all individual recaptured red snapper growth rates.
Environmental Variables
Spearman (PROC CORR Spearman, SAS Institute version 9.2, 2008) productmoment correlation (r) was used to test for correlations among red snapper CPUE
(fish/hour) and environmental variables measured in the bottom of the water column.
As a nonparametric measure of association, Spearman correlation analysis does not
require the assumption of normality to be met.
For visual analysis, environmental parameter distributions were tested for
normality using normal probability plots and Shapiro-Wilk values generated from
14
PROC UNIVARIATE (SAS Institute Inc., Cary N.C. 2008) and a square root
transformation was applied to the dissolved oxygen data to satisfy the assumptions of
normality. Scatter plots of natural log transformed CPUE versus square root
transformed DO, salinity, and temperature were created for trend analysis.
15
CHAPTER 3
RESULTS
Sampling
Sampling for this project began September 28, 2007, and ended November 20,
2008. Twenty six (26) trips were made to FH-13 for data collection. Section B was
visited most often (N=11), whereas Section A was sampled eight times and Section C
was visited seven times (Table 2). Reef patterns within each section were sampled
fairly evenly. The clump pattern was visited the most times (N=22), whereas the
OL200 was visited the least number of times (N=17) (Table 3). Sampling throughout
the seasons was fairly similar among patterns. During the period January-May,
sampling was limited because of adverse weather and sea conditions. From
September 2007 through May 2008, nine sampling trips were taken. From June 2008
through November 2008, 17 trips were taken.
Catch Composition
There were 1402 fish (21 species) captured during sampling at site FH-13
(Appendix A). Red snapper made up most of the total catch (66%; N=927), with gray
triggerfish making up the next greatest percentage (10%, N=139). Lane snapper was
the only other species that consisted of more than 5% of the total catch (6%, N=81).
The greatest number of species were collected at the clump pattern (N=19), whereas
16
the least number of species were collected at the OL200 and OL300 patterns (N=12
each).
Catch per Unit of Effort (CPUE)
Catch per unit of effort (CPUE) of red snapper was determined for each
pattern on every individual trip. Estimates of CPUE differed from trip to trip at each
individual pattern for Section A (Table 4), Section B (Table 5), and Section C (Table
6). Results from the best fit mixed model (AICc=101.0) indicate CPUE did not vary
significantly among different reef patterns (reef pattern: F3, 69.2=1.00; P=0.396), but
CPUE did differ significantly among seasons (season: F2, 69.5=6.56; P=0.002). The
inclusion of section as a random effect in the model did not improve model likelihood
as the estimate was close to zero (estimate= 0.026, SE= 0.033). The geometric least
squares parameter estimates of mean CPUE for the clump (mean CPUE= 1.22 fish/h;
SE= 0.33), OL100 (mean CPUE= 1.38 fish/h; SE= 0.32), OL200 (mean CPUE= 1.57
fish/h; SE= 0.43), and OL300 (mean CPUE= 1.11 fish/h; SE= 0.28) patterns were
similar (Figure 4).
Bonferroni adjusted least squares pair-wise comparisons analysis indicated
that mean CPUE differed significantly between the spring and summer seasons
(P=0.001), but did not differ significantly between spring and fall (P=1.000) and
summer and fall (P=0.175). For season, geometric least squares parameter estimates
of mean CPUE was largest for summer (mean CPUE= 1.74 fish/h; SE= 0.38),
whereas the spring season had the smallest estimated mean CPUE (mean CPUE=
1.06 fish/h; SE= 0.24). The estimated mean CPUE for fall (mean CPUE= 1.19 fish/h;
17
SE= 0.73) did not differ significantly from the spring and summer mean CPUE
estimates (Figure 5).
Mean Length
The mean total length of red snapper collected in this study was 225.38 mm
(SE= 2.24). Of the 927 red snapper captured, only 18 exceeded the legal length limit
of 406 mm TL. Results from the mixed model (AICc= 231.8) indicated that mean TL
differed among the four patterns (F3, 25.2= 5.39; P= 0.005) and among the seasons
(F2, 42.6= 6.22; P= 0.004). The inclusion of section as a random effect in the model
did not improve model likelihood as the estimate was close to zero (estimate= 0.593,
SE= 0.70).
Bonferroni adjusted least squares pair-wise comparisons analysis indicated
that mean TL differed significantly between the OL200 pattern and the clump (P=
0.003) pattern (Figure 6). No other comparison of mean TL between patterns yielded
significant results (P > 0.05). Geometric least squares parameter estimates of mean
TL indicated that the OL200 pattern had the largest mean TL (mean TL= 253.16 mm,
SE= 17.44) whereas the clump pattern had the smallest mean TL (mean TL= 203.54
mm, SE=16.71). The OL100 pattern (mean TL= 231.47 mm, SE= 16.43) and OL300
pattern (mean TL= 224.59 mm, SE= 17.55) had similar mean TL (Figure 6).
Results from the Bonferroni adjusted least squares pair-wise comparisons
analysis indicated that mean TL differed significantly between fall and spring (P=
0.029) and fall and summer (P= 0.004), but not spring and summer (P= 1.000)
(Figure 7). Geometric least squares parameter estimates of mean TL indicated that
the fall season had the largest mean TL (mean TL= 251.06 mm, SE= 18.30). The
18
mean TL for spring (mean TL= 219.12 mm, SE= 17.07) and summer (mean TL=
214.21 mm, SE= 13.83) did not significantly differ (Figure 7). Red snapper length
frequency distributions by pattern and season show that most captured red snapper
were between 125-275 mm (TL) (Figure 8 and Figure 9, respectively).
Species Diversity
Results from the mixed model analysis (AICc= 101.3) indicated that H’
(F1,69.4= 0.81; P= 0.371) and the H’*pattern interaction (F3,65.8= 0.42; P= 0.737) did
not significantly affect red snapper CPUE. The inclusion of section as a random
variable did not increase model likelihood as the parameter estimate was close to zero
(estimate= 0.020, SE= 0.027).
For TL, results from the mixed model analysis (AICc= 243.9) indicated that
H’ (F1,62= 0.05; P= 0.823) and the H’*pattern interaction (F3,39.8= 2.42; P= 0.081) did
not significantly affect red snapper TL. Including section as a random variable did
not increase model likelihood as the parameter estimate was close to zero (estimate=
0.735, SE= 0.910).
Tag Return
I tagged a total of 852 red snapper. The discrepancy between total red
snapper captured (927) and the total number of red snapper tagged (852) was due to a
sampling trip October 26, 2007 when no tagging gun was brought on the trip, and a
sampling trip April 22, 2008 when both tagging guns broke. Thirty one (31) red
snapper were recaptured (Table 7). Two red snapper were recaptured twice, but one
had lost its original tag. Overall I had a tag return rate of 4% for red snapper. Only
19
one red snapper was recaptured at a site other than its original site of tagging. It was
originally tagged at the OL100 pattern in Section B and was recaptured at the OL200
pattern in Section B. That gives a 97% site fidelity estimate for recaptured red
snapper (N=31).
One red snapper was at large for 256 days before recapture (Table 7).
Including that recapture, the average time at large for recaptures was 36 days.
Excluding that particular specimen, the average time at large for red snapper
recaptured during sampling was 21 days.
Growth
The change in TL for recaptured red snapper was divided by the days at
liberty to get an estimate of the mean growth rate of recaptured red snapper. The
growth rate estimate for recaptured red snapper was 0.29 mm/day (SE= 0.04; N=31)
(Table 7). Looking at growth rates for individual patterns, the OL200 pattern
produced the largest mean growth rate [mean= 0.47 mm/d (TL); SE= 0.08; N= 11],
followed by the clump [mean= 0.23 mm/d (TL); SE= 0.04; N= 11], and OL100
[mean= 0.18 mm/d (TL); SE= 0.04; N= 9] patterns. Only one recapture came from
the OL300 pattern, and that fish’s growth rate was 0.05 mm/d (TL).
Environmental Variables
Results from the Spearman correlation analysis indicated no significant
correlations between red snapper CPUE and salinity (Spearman r = -0.13, P= 0.32),
dissolved oxygen (Spearman r = -0.07, P= 0.58) or temperature (Spearman r = 0.12,
P= 0.35). Scatter plots of natural log transformed CPUE versus salinity (R2= 0.006),
20
square root transformed dissolved oxygen (R2= 0.004), and temperature (R2= 0.027)
revealed no strong patterns (Figure 10).
Post-Capture Condition
Eight hundred and ninety eight of the captured red snapper were considered to
be in “Good” condition after release, 24 red snapper were considered to be in “Fair”
condition after release, and five red snapper were considered to be “Dead” after
release (Table 8). Of the 29 red snapper determined to be in “Fair” condition or
“Dead”, only 22 were tagged, which gave an estimated acute mortality rate of 3% due
to the tagging process for red snapper in my study.
21
CHAPTER 4
DISCUSSION
My study was developed to examine the effects of reef spacing and horizontal
extension on juvenile red snapper, with the hope of finding specific spatial patterns
that would most benefit juvenile snapper and in turn aid in stock enhancement.
Though there have been studies that have examined artificial reef structural
characteristics and placement strategies with respect to maximum fisheries benefits
for artificial reef programs (Gregg 1995; Harrera et al. 2002; Strelcheck et al. 2005),
few studies have specifically examined the importance of reef spacing and placement
for red snapper management.
The limited information on these important reef aspects belies the importance
of my study. In this regard, my focus on juvenile red snapper habitat preference is
particularly important because recruitment variability and year class strength of red
snapper are most likely determined during early life stages (Geary et al. 2007). The
significance of juvenile survival makes identifying habitats or conditions that favor
survival during early life stages critical to management.
Results from this study indicate that juvenile red snapper are recruiting to the
artificial reef structures that I studied. Ninety-eight percent of the red snapper caught
during my study (909 fish) were under the legal recreational length limit of 406 mm
(TL), and the mean length of red snapper captured was 225 mm (TL). Wells and
22
Cowan (2007) found that juvenile red snapper recruit to high relief structures at 20
cm (TL), or at age-1, and Nieland and Wilson (2003) found that juvenile red snapper
disappear from shrimp trawls at age-1, migrating to higher relief structures to seek
refuge from predators. Because juvenile red snapper in my study area utilized the
artificial reef structures, the reefs must be providing some benefit for these fish,
possibly as refuge from predation or in terms of increased foraging opportunities.
Perhaps the most significant function of the artificial reefs in my study is their
use as refuge for juvenile red snapper from shrimp trawls, as reduction in red snapper
bycatch mortality from shrimp trawling could play a key role in red snapper stock
rehabilitation (Peabody 2004). Gallaway et al. (1999) found that juvenile red snapper
reach full vulnerability to shrimp trawls around 100 mm (TL). Because many of the
red snapper that I captured were between 100-200 mm (TL), the artificial reefs in my
study area could be providing important refuge for juvenile red snapper that would
otherwise be lost as bycatch in shrimp trawls.
Catch per Unit of Effort (CPUE)
Results from the mixed model analysis indicated that reef pattern did not
significantly affect red snapper CPUE, as all mean pattern CPUE estimates differed
by < 1 fish/hour. As the primary objective of this study, a lack of significant pattern
affects on red snapper relative abundance was unexpected. A variety of factors may
have led to this result.
Difficulties related to setting traps on, or in close proximity to, the sampled
reef patterns, even when taking into account important factors such as currents and
wave action, may have played a prominent role in my inability to find significant
23
pattern effects on red snapper relative abundance. The ever changing resting place of
traps in proximity to the sampled patterns may have led to the large observed
fluctuations in CPUE within patterns from trip to trip, and among traps set on a given
reef. Different robust estimates of scale such as interquartile range and median
absolute deviation from the median were examined to determine an appropriate
estimate of variation from trip to trip and among traps, that could be used in
significance testing. However, my small sample size and number of traps used did
not work well with the robust estimates that were examined, and results generated
from those estimators were misleading.
Reef populations that were not yet in equilibrium may have also lead to my
inability to decipher reef pattern effects on CPUE. Bohnsack and Sutherland (1985)
stated that reef fish populations may reach maximum population size within a few
months after the reefs are placed in the environment, and equilibrium community
structure is usually achieved within one to five years. Sampling for this study began
about three months after the last study reef was placed in the study area, and all
sampling occurred within a year and a half of the final placement of the study reefs. I
believe that red snapper which had recruited to my study reefs were still in the
process of reaching maximum population size and equilibrium population structure.
If the populations were not yet at a sustainable maximum size and new juvenile red
snapper were recruiting continuously to the structures during the period of my study,
then the use of CPUE as an index of relative abundance may have given biased
results which in turn would make it difficult to determine statistically significant
differences in red snapper relative abundance among the different reef patterns.
24
Though there was no significant influence of pattern on CPUE, relationships
from my data indicated that the OL200 pattern produced the largest CPUE of juvenile
red snapper, which is similar to the findings of Frazer and Lindberg (1994). They
looked at different reef spacing of similar sized prefabricated concrete reefs and
found widely spaced reef units (60 m) had a larger abundance of gray triggerfish and
black sea bass (Centropristis striata) than closely spaced units (2 m), which may have
been due to density dependent interactions specifically linked to foraging area and
prey resources.
The importance of reef spacing may be directly linked to red snapper foraging
strategies and the principles of the Optimal Foraging Theory and Resource Mosaic
Hypothesis (McCawley 2003). Juvenile red snapper diets are largely comprised of
soft bottom prey resources. As the distance between reef units decreases so too does
the access to soft bottom prey around the reef and areas of intense depletion called
foraging halos develop (McCawley and Cowan 2007). If reefs are placed too close
together, their associated foraging halos may overlap and negatively affect one
another by causing a disproportional depletion of resources. Red snapper associated
with closely spaced reefs may be forced to travel farther from the reef to forage at
increased energetic cost which in turn increases the risk of predation and decreases
the probability that those snapper will return to the reef leading to potential declines
in abundance (McDonough 2009; Westmeyer et al. 2007; Frazer and Lindberg 1994).
In this regard, the OL200 pattern may provide an adequate amount of spacing
to minimize halo overlap and in turn may be able to support a greater abundance of
red snapper. Though the OL300 pattern has wider spacing and in theory even less
25
foraging overlap, it is possible that the outliers of the OL300 pattern are far enough
from the main clump that juvenile red snapper that venture within proximity of the
outliers may decide to stay instead of risk predation traveling back to the main clump.
With the closer proximity of the outlier structures of the OL200 pattern, juvenile red
snapper may be more willing to move freely between the main clumps and outliers
utilizing the extra structure for refuge from predation and areas of additional foraging
opportunities.
As expected, CPUE of juvenile red snapper differed significantly among
seasons. For my study the summer season produced the largest CPUE, which runs
counter to previous studies. Strelcheck (2001) and Patterson (1999) found CPUE of
red snapper to decrease during spring and summer, and increase in the fall. However,
both of these studies involved red snapper of larger mean size than those in my study.
The presence of larger red snapper on my study reefs during the fall season
may be one reason for my observed seasonal differences in CPUE. Bailey (1995)
found that the presence of larger sub-adult red snapper (360-367 mm) negatively
influenced the presence of young of the year red snapper by limiting refuge and
foraging opportunities. For my study the fall season had the largest mean TL, and the
presence of larger red snapper during the fall and early spring may have had a
negative effect on juvenile red snapper CPUE.
Mean Length
Results from the mixed model analysis indicated that mean TL of red snapper
differed significantly among patterns, with the OL200 pattern having the largest
estimated mean TL. Significant differences in mean TL between patterns may be an
26
indication of increased benefits (foraging opportunities, prey abundance) specific to
pattern type or reef location. Powers et al. (2003) and Wells (2007) found that larger
sizes of individual fish at particular reefs may be an indication of increased refuge
from predation and an increased access to reef associated prey resources, which in
turn may lead to an increase in production by enhancing growth and protection of
individuals utilizing the reefs.
Similar reasons to those explained for my CPUE results apply in terms of why
red snapper associated with the OL200 pattern had significantly larger mean TL. The
OL200 design may offer the appropriate reef spacing for juvenile red snapper which
in turn may increase prey access and foraging opportunities while minimizing the risk
of predation. The greater distance between the main clump and outliers of the OL300
patterns may be too large for juvenile red snapper to move between freely, and the
energetic costs associated with increased forage searching time and predator
avoidance may have lead to slower growth rates and smaller mean TL.
Red snapper mean TL differed significantly among seasons, with the fall
season producing the largest mean TL. The collection of larger juvenile red snapper
in the fall seems reasonable as the fish had more time to grow, but as mentioned
earlier, the larger mean TL for the fall season may be a result of the movement of
larger red snapper onto the artificial reefs used during my study. Wells (2007) found
that seasonal size differences at specific reef habitats may likely be a result of
seasonal emigration and immigration of different size groups of red snapper. The
possible movement of larger fish onto my study reefs in the fall could account for the
27
larger mean total length and smaller mean CPUE of red snapper during the fall
season.
Species Diversity
The analysis of species diversity indicated that H’ and H’*pattern interaction
did not significantly affect red snapper CPUE or TL. It is important to point out that
the traps used were selective for certain sizes of fish and species that would be
attracted by cut-bait. As such, the diversity I observed may not be representative of
the true species diversity of my sample reefs. A variety of collection gear and visual
analysis would be needed to gain truly accurate species diversity estimates.
Additionally, as I mentioned before, the community structures of my study reefs may
had not reached equilibrium during my study period which could affect analysis, or
the species that I observed from sampling may occupy different niches and not
significantly affect red snapper relative abundance.
Growth
The mean growth rate for red snapper during my study (0.29 mm/day)
indicates similar growth to previous studies of red snapper. Patterson et al. (2001b)
found the growth rate of tagged red snapper to be 0.24 mm/day (TL), although the
mean length of red snapper in their study was larger (mean= 335 mm TL) than the
mean length of red snapper in my study. Watterson (1998) found that fish tagged at
initial lengths less than 300 mm (TL) exhibited a larger growth rate of 0.36 mm/day
compared to 0.23 mm/day for red snapper between 300-399 mm.
28
The OL200 pattern had the fastest mean growth rate among the patterns.
Although sample sizes were not large enough for statistical tests, the faster growth
rate for the OL200 pattern may be another indication that the OL200 pattern design
offers significant benefits to the juvenile red snapper in the study area, which in turn
may lead to increased production through increased abundance and biomass (Powers
et al. 2003 and Wells 2007). If red snapper that utilize the OL200 patterns are able to
translate added benefits into quicker growth, they would be able to move quickly out
of vulnerable juvenile stages and avoid predation (Wells 2007). The faster estimated
growth rate from the OL200 recaptures may offer some explanation as to why I saw
the significantly larger mean TL for that pattern as well.
Tag Return
The site fidelity estimate for recaptured red snapper in this study was 97%,
which falls in line with other studies involving juvenile red snapper. Strelcheck et al.
(2007) and Workman et al. (2002) found that juvenile red snapper exhibit high site
fidelity, and homing abilities when displaced from structure. Diamond et al. (2007)
found that 96% of tagged red snapper in their study that were small [< 379 mm (TL)]
and captured in shallow water (< 40 m) stayed at their original tagging site, which is
very similar to my study as all of my recaptured red snapper were < 379 mm (TL) and
captured in water < 40 m deep. Diamond et al. (2007) believe that reef fish taken
from shallower water (< 30 m) move less than fish taken from deeper water, most
likely because shallow water generally has higher productivity.
One red snapper in my study was recaptured at a site other than that of its
original tagging, and that fish moved from the OL100 pattern in Section B to the
29
OL200 pattern in Section B. This provides further evidence for the suitability of the
OL200 pattern for juvenile red snapper, as high site fidelity may be a strong
indication of habitat suitability (McDonough 2009).
I recorded a tag return rate of 4% for red snapper, which is similar to results
from other studies. Diamond et al. (2007) found the tag return rate for red snapper in
their study to be 2.3%, but Patterson (2007) found that tag return rates for red snapper
studies have varied between 2.8-35%. I noticed from recaptured fish that
considerable bio-fouling of tags occurred after relatively short periods of time at
large, making the tag hard to see without careful examination. It is possible that some
captured undersized red snapper were quickly released by fishermen without them
noticing tags, which may be why I have not had any reported tag returns outside of
what I collected.
High rates of tag loss may have also been a direct factor in the low tag return
rate. A double-tagging study of striped bass Morone saxatilis found t-bar anchor tag
retention to be as low as 42% after just one year (Dunning et al. 1987). Muoneke
(1992) found the rate of t-bar anchor tag loss for white bass (Morone chrysops) to be
24.8%. Of the two red snapper that were recaptured twice (double tagged) in my
study, one had lost its first tag which may be a strong indication of low tag retention.
On top of tag loss, another drawback to tagging with t-bar anchor tags is that
even if fish show high site fidelity, it is impossible to know if or how the fish moved
between capture and recapture (Watterson 1998; Szedlmayer and Schroepfer 2005).
Recaptured fish in my study may have moved off of the reefs and returned, and fish
that were not recaptured may have undertaken extensive movements. With no
30
information from the tagged fish that were not recaptured, my site fidelity estimate
must be viewed with caution and strict understanding that the estimate is only for
those fish that were recaptured.
Environmental Variables
No significant correlations between juvenile red snapper CPUE and measured
environmental variables were observed which is similar to the study of Strelcheck
(2001), as he did not find significant correlations between red snapper CPUE and
temperature or red snapper CPUE and DO. Environmental variables measured during
my study period may not have differed enough from trip to trip to produce a
significant effect on red snapper CPUE. Interestingly, my largest single estimated
trip CPUE occurred with a bottom DO measurement of 1.94 mg/L, which is well
below the preferred DO level of 5.0 mg/L for juvenile red snapper determined by
Gallaway and Cole (1999). Measurement error associated with the YSI meter may
explain this observation, or juvenile red snapper in my study area with limited refuge
options may tolerate adverse environmental conditions to avoid the risk of predation.
Post-Capture Condition
Acute mortality of juvenile red snapper from the tagging process for this study
was fairly low. Patterson et al. (2001a) looked at acute mortality in captured red
snapper due to the tagging process. For their study, they created four condition
categories and assumed that fish released in any condition other than the best possible
suffered acute mortality as result of the tagging process. In their study, 14% of the
tagged red snapper were released in a condition other than the best possible and were
31
assumed to have suffered acute mortality from the tagging process. Following similar
guidelines, I found a smaller acute mortality of 3% due to the tagging process for my
captured red snapper. All recaptured red snapper in my study were originally
released in the best possible condition (condition 1), which gives some credence to
the use of that particular grading system as an index for acute tagging mortality.
The relatively small mortality rate from the tagging process was promising, as
there was some concern as to how well the smaller, pre-recruit red snapper would
handle tagging. It appears that my use of t-bar anchor tags did not significantly affect
release mortality of captured red snapper. Gitschlag and Renaud (1994) looked at
survival rates of red snapper [25-43 cm (FL)] captured at different depths, and found
90% of the red snapper collected from depths between 27-30 meters (the depth range
covering our study area) survived the retrieval process, and size of fish did not
influence mortality. The slow retrieval of the traps by hand and relatively shallow
sampling depths in my study may have been beneficial in terms of survival of
captured fish.
Conclusions
Findings of this study are significant and promising, as few studies have
looked at the importance of spacing and horizontal extension as they pertain to the
recruitment of juvenile red snapper to artificial reef structures and their retention on
those structures. Juvenile red snapper are recruiting to the pyramid shaped artificial
reef structures, which may lead to a decrease in juvenile red snapper bycatch
mortality as the fish move off of the shrimp grounds and onto the reefs for refuge.
The rapid colonization of the artificial reef structures gives a strong indication that the
32
reefs are offering benefits to the fitness of these important reef fish species, whether it
be increased shelter from predation or increased foraging opportunities.
Though no significant differences were found in mean CPUE of red snapper
by pattern, results from my data indicate that the OL200 pattern had the largest mean
CPUE. The largest mean TL of collected red snapper also came from the OL200
pattern, which may indicate energetic benefits related to the specific reef spacing of
that pattern. The faster mean growth rate of recaptured red snapper from OL200
pattern, and the fact that the only recapture that moved relocated to an OL200 pattern
gives further evidence to some benefit or benefits that juvenile red snapper are able to
exploit that is/are not found in the other three experimental patterns. Continued
research of red snapper on my study reefs that examines important physiological and
ecological aspects such as diet, prey availability, and interactions with other species
could help address some of the questions my study was unable to answer.
Particularly, why the mean TL and growth rate for red snapper at the OL200 patterns
is larger than for the other patterns I tested.
Reef spacing is just one physical component of artificial reef complexes that
may affect red snapper and other reef fish recruitment to the structures. The
consequences of resource depletion caused by overlapping foraging halos are a
critical reason why management of artificial reefs should consider reef spacing to
minimize halo overlap. Though initial costs may be higher, my results reflect the
importance of species specific studies that analyze specific habitat preferences and
what characteristics of those habitats that are most important to the chosen species.
For artificial reefs to best aid in the rehabilitation of depleted red snapper stocks,
33
continued analysis of artificial reef physical characteristics that best benefit different
life history stages must be undertaken. The results of this study provide an important
and informative first step towards the understanding of the relationship between
juvenile red snapper and artificial reefs off the coast of Mississippi, which will
hopefully aid in the rehabilitation of red snapper stocks Gulf wide.
Reef Balls versus Pyramids
I was given additional information from a new project initiated by the
Artificial Reef Bureau of the MSDMR looking at differences in prefabricated
artificial reef materials. As artificial reefs become more prevalent in marine systems
management, so too will the options of prefabricated materials. Studies that examine
the effects of different prefabricated reef material on target fish species will be
necessary to help managers best elicit desired results. This newly initiated study by
the MSDMR is the first step towards better understanding the different effects that
pyramid shaped concrete and limestone structures and concrete Goliath Reef Balls
(GRB) have on red snapper and gray triggerfish CPUE and TL.
For this study, pyramid shaped artificial structures and Goliath Reef Balls
were placed in designated artificial reef sites FH-1 and FH-2, which are both located
in close proximity to my study site FH-13 or about 40 km south of Pascagoula,
Mississippi. Size specifications for the pyramid structures can be found in the
methods section of this report. Goliath Reef Balls are composed of concrete, measure
1.83 m wide by 1.52 m tall, and weigh about 2.27 mt. Pyramid structures and GRBs
were placed in clumps of 10 structures throughout FH-2 and FH-1. Three sets each of
10 structures were placed in each reef site.
34
Sampling took place in a similar manner as sampling for my study. Identical
trap nets as used for my study were used to collect fish. After a sample reef was
selected, three traps were set on the clump of pyramids or GRBs and allowed to soak
for two hours. After soaking for two hours, the traps were collected one at a time by
hand, and the contents of each trap enumerated. Red snapper, gray triggerfish, gag
grouper, and lane snapper were tagged with gray FLOY® (FLOY Tag and
Manufacturing Incorporated, Seattle, Washington) t-bar anchor tags, and each fish
was measured for fork and total lengths.
Statistical analysis was performed on the preliminary data. The effects of the
two different materials on red snapper and gray triggerfish relative abundance and TL
were examined. Catch per unit of effort (CPUE) was used as an index of relative
abundance. Red snapper and gray triggerfish CPUE (fish/hour) and TL (mm) data
were tested for normality using normal probability plots and Shapiro-Wilk values
generated from PROC UNIVARIATE (SAS Institute Inc., Cary N.C. 2008). The data
were found to follow normal distributions. Analysis was run using general linear
models (PROC GLM, SAS Institute Inc., Cary N.C. 2008). Models directly assessed
the effect of reef type (independent variable) on CPUE and TL (dependent variables).
An alpha level of 0.05 was used for analysis.
To date, the pyramid structures were visited eight times and the GRBs were
visited four times (12 total visits). A total of 327 red snapper and 20 gray triggerfish
were collected, with 100 red snapper and seven gray triggerfish collected from GRBs
and 227 red snapper and 13 gray triggerfish collected from pyramid structures.
Statistical analysis indicated that reef type did not significantly affect red snapper
35
mean CPUE (F= 0.09, P= 0.776), but reef type did have a significant effect on red
snapper mean TL (F= 9.12, P= 0.0145). Red snapper mean CPUE estimates for
pyramids (mean CPUE= 4.728 fish/hour, SE= 1.180) and GRBs (mean CPUE= 4.166
fish/hour, SE= 1.32) were similar, but red snapper mean TL estimates for pyramids
(mean TL= 282.168 mm, SE= 9.259) and GRBs (mean TL= 242.689 mm, SE= 5.111)
differed by 40 mm.
For gray triggerfish, statistical analysis indicated that gray triggerfish mean
CPUE (F= 0.33, P= 0.579) and mean TL (F= 0.17, P= 0.692) were not significantly
affected by reef type. Gray triggerfish mean CPUE estimates for pyramids (mean
CPUE= 0.208, SE= 0.087) and GRBs (mean CPUE= 0.291, SE= 0.104) were similar,
and mean TL estimates for pyramids (mean TL= 281.066, SE= 16.981) and GRBs
(mean TL= 261.833, SE= 55.352) differed by approximately 20 mm.
As preliminary analysis, these results must be taken with caution. Statistical
analysis and mean estimates were drawn off of a small sample size (12 samples), and
the GRBs were visited half as many times as the pyramids. With unbalanced data,
statistical results can be misleading. As the only significant result, it does appear that
pyramids have larger red snapper which may be a result of faster growth or the use of
the pyramids by larger, older red snapper. Further research will give a better
understanding of the effects of the two different reef materials on red snapper, gray
triggerfish, and other important bycatch species CPUE and TL, and provide crucial
information on an important artificial reef characteristic.
36
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42
Tables
43
Table 1. Latitudinal and longitudinal coordinates for the sections of artificial reef site FH-13 located offshore of Mississippi in
the Gulf of Mexico and sampled during the period of September 2007 through November 2008.
Northwest
Corner
Northeast
Corner
Northeast
Corner2
Southwest
Corner
Southeast
Corner
A
30 04.000N
88 32.400W
30 04.000N
88 31.700W
30 01.700N
88 29.300W
30 01.374N
88 32.406W
30 01.374N
88 29.300W
B
30 01.374N
88 32.406W
30 01.374N
88 29.300W
30 00.240N
88 32.406W
30 00.240N
88 29.300W
C
30 00.240N
88 32.406W
30 00.240N
88 29.300W
29 59.200N
88 32.400W
29 59.200N
88 29.300W
Section
44
Table 2. Latitudinal and longitudinal coordinates for each artificial reef pattern and total visits to each section and artificial
reef pattern in artificial reef site FH-13 located offshore of Mississippi in the Gulf of Mexico and sampled during the
period of September 2007 through November 2008.
Section
Latitude
Longitude
Depth (m)
Total Pattern Visitis
A
Clump
OL100
OL200
OL300
30 03.734N
30 03.770N
30 02.242N
30 01.960N
88 32.339W
88 31.506W
88 30.120W
88 30.645W
21.3
20.4
24.0
24.0
8
5
4
6
B
Clump
OL100
OL200
OL300
30 00.760N
30 01.141N
30 00.697N
30 01.129N
88 31.591W
88 29.531W
88 29.544W
88 31.009W
25.0
25.3
25.3
25.0
8
9
7
9
C
Clump
OL100
OL200
OL300
30 00.178N
30 00.013N
29 59.833N
29 59.713N
88 30.471W
88 32.009W
88 31.594W
88 31.154W
26.0
26.0
26.2
26.8
6
6
5
4
45
Pattern
Table 3. Number of total visits to each pattern and total number of pattern visits by
season at artificial reef site FH-13 located offshore of Mississippi in the
Gulf of Mexico and sampled during the period of September 2007 through
November 2008.
Season
Clump
Pattern
OL100
Spring
5
6
5
6
Summer
11
11
7
7
Fall
6
3
5
6
Total
22
20
17
19
46
OL200
OL300
Table 4. Catch per unit effort (CPUE, red snapper/trap soak hour) of red snapper for
each trip to individual artificial reef patterns in Section A of artificial reef
site FH-13 located offshore of Mississippi in the Gulf of Mexico and
sampled during the period of September 2007 through November 2008.
Location
Date
Traps Set
Total Red Snapper
CPUE (red snapper/trap soak hour)
A Clump
10/26/2007
3/12/2008
4/22/2008
7/2/2008
7/16/2008
8/7/2008
10/3/2008
11/5/2008
3*
4
3**
3**
4
4
3**
4
7
5
12
43
19
2
10
18
1.17
0.63
2.00
7.17
2.38
0.25
1.67
2.25
3*
4
4
4
4
6
7
16
13
29
1.00
0.88
2.00
1.63
3.63
3**
4
4
4
11
3
31
16
1.83
0.38
3.88
2.00
4
4
3***
4
4
4
7
33
29
18
11
14
0.88
4.13
4.83
2.25
1.38
1.75
N=8
A OL100
10/26/2007
3/12/2008
4/22/2008
7/2/2008
7/16/2008
N=5
A OL200
7/2/2008
8/7/2008
10/3/2008
11/5/2008
N=4
A OL300
3/12/2008
4/22/2008
7/16/2008
8/7/2008
10/3/2008
11/5/2008
N=6
*Only 3 traps were used per reef pattern on particular sampling trip.
**Trap broken on pyramid upon retrieval.
***Rope became unattached from buoy upon retrieval, trap lost.
47
Table 5. Catch per unit effort (CPUE, red snapper/trap soak hour) of red snapper for
each trip to individual artificial reef patterns in Section B of artificial reef
site FH-13 located offshore of Mississippi in the Gulf of Mexico and
sampled during the period of September 2007 through November 2008.
Location
Date
Traps Set
Total Red Snapper
CPUE (red snapper/trap soak hour)
B Clump
9/28/2007
3/6/2008
4/30/2008
6/3/2008
6/10/2008
7/10/2008
7/17/2008
9/18/2008
4
4
4
4
4
4
4
4
2
6
10
8
1
16
7
10
0.25
0.75
1.25
1.02
0.13
2.01
0.88
1.25
4
4
4
4
4
4
4
4
4
4
0
19
2
23
25
16
16
17
0.50
0.00
2.38
0.25
2.88
3.13
2.00
2.00
2.13
4
4
4
4
4
4
4
10
10
6
1
22
10
18
1.25
1.25
0.75
0.13
2.75
1.25
2.25
4
4
4
4
4
4
3*
4
4
11
3
5
13
4
10
8
4
2
1.38
0.38
0.63
1.63
0.50
1.25
1.33
0.50
0.25
N=8
B OL100
9/28/2007
3/6/2008
4/2/2008
6/3/2008
6/10/2008
7/10/2008
7/17/2008
8/21/2008
11/20/2008
N=9
B OL200
3/6/2008
4/2/2008
4/30/2008
7/10/2008
8/21/2008
9/18/2008
11/20/2008
N=7
B OL300
9/28/2007
4/2/2008
4/30/2008
6/3/2008
6/10/2008
7/17/2008
8/21/2008
9/18/2008
11/20/2008
N=9
*Broken Trap
48
Table 6. Catch per unit effort (CPUE, red snapper/trap soak hour) of red snapper for
each trip to individual artificial reef patterns in Section C of artificial reef
site FH-13 located offshore of Mississippi in the Gulf of Mexico and
sampled during the period of September 2007 through November 2008.
Location
Date
Traps Set
Total Red Snapper
CPUE (red snapper/trap soak hour)
C Clump
5/28/2008
6/16/2008
6/19/2008
6/24/2008
7/8/2008
11/6/2008
4
4
3*
4
4
4
3
23
9
26
19
3
0.38
2.88
1.50
3.25
2.38
0.38
4
4
4
4
4
4
4
9
19
6
24
7
0.50
1.13
2.38
0.75
3.00
0.88
4
4
4
3*
4
13
15
17
18
14
1.63
1.88
2.13
3.00
1.75
4
4
4
4
9
3
7
0
1.13
0.38
0.88
0.00
N=6
C OL100
5/28/2008
5/30/2008
6/16/2008
6/19/2008
6/24/2008
7/8/2008
N=6
C OL200
5/30/2008
6/19/2008
6/24/2008
7/8/2008
11/6/2008
N=5
C OL300
5/28/2008
5/30/2008
6/16/2008
11/6/2008
N=4
*Broken trap
49
Table 7. Recapture data for red snapper captured with trap nets during sampling from
September 2007 through November 2008 at artificial reef site FH-13 off the
coast of Mississippi in the Gulf of Mexico.
Capture
Capture
Recapture
Recapture
Days at
Total Length
Growth
Date
Site
Date
Site
Large
Increase (mm)
(mm/day)
3/12/2008
A Clump
4/22/2008
A Clump
41
10
0.24
4/2/2008
B OL300
6/3/2008
B OL300
62
3
0.05
9/28/2007
B OL100
6/10/2008
B OL100
256
51
0.20
6/16/2008
C OL100
6/24/2008
C OL100
8
1
0.13
6/16/2008
C OL100
6/24/2008
C OL100
8
1
0.13
6/16/2008
C OL100
6/24/2008
C OL100
8
1
0.13
5/30/2008
C OL100
6/24/2008
C OL100
25
7
0.28
5/30/2008
C OL200
6/24/2008
C OL200
25
8
0.32
6/19/2008
C OL200
6/24/2008
C OL200
5
6
1.20
6/19/2008
C Clump
6/24/2008
C Clump
5
2
0.40
6/24/2008
C OL200
7/8/2008
C OL200
14
3
0.21
6/24/2008
C OL200
7/8/2008
C OL200
14
7
0.50
6/19/2008
C OL200
7/8/2008
C OL200
19
8
0.42
6/19/2008
5/30/2008*
C OL200
7/8/2008
C OL200
19
7
0.37
C OL200
7/8/2008
C OL200
39
8
0.21
6/24/2008
C Clump
7/8/2008
C Clump
14
5
0.33
6/24/2008
C Clump
7/8/2008
C Clump
14
no growth
0.00
6/19/2008
C Clump
7/8/2008
C Clump
19
1
0.05
6/16/2008
C Clump
7/8/2008
C Clump
22
6
0.27
6/16/2008
C Clump
7/8/2008
C Clump
22
5
0.23
6/3/2008
B Clump
7/10/2008
B Clump
37
13
0.35
7/2/2008
A Clump
7/16/2008
A Clump
14
no growth
0.00
7/2/2008
A Clump
7/16/2008
A Clump
14
5
0.36
6/3/2008
B Clump
7/17/2008
B Clump
44
12
0.27
7/10/2008
B OL100
8/21/2008
B OL100
42
3
0.07
7/10/2008
B OL100
8/21/2008
B OL100
42
2
0.05
7/10/2008
B OL100
8/21/2008
B OL100
42
10
0.24
7/10/2008
B OL100
8/21/2008
B OL200
42
17
0.40
7/2/2008
A OL200
10/3/2008
A OL200
93
39
0.42
8/7/2008
10/3/2008*
A OL200
10/3/2008
A OL200
57
32
0.56
A OL200
11/5/2208
A OL200
33
17
0.52
N=31
*Double recapture
50
Table 8. Condition and location of capture of red snapper which were released in any
condition other than the best possible (Good) after being captured with trap
nets from September 2007 through November 2008 at artificial reef site FH13 off the coast of Mississippi in the Gulf of Mexico.
Location of Capture
Date Captured
Tagged
Condition
A OL200
A OL300
A OL300
A OL300
B OL100
B OL100
B Clump
C OL200
A OL100
C OL100
C OL100
C Clump
C OL100
B OL100
B OL300
C OL200
A OL300
A OL300
A OL300
A OL300
A OL300
A OL300
A OL300
A OL300
B OL100
B OL100
B OL200
B OL200
B OL300
8/7/2008
8/7/2008
7/16/2008
7/16/2008
7/10/2008
7/10/2008
7/10/2008
7/8/2008
7/2/2008
6/24/2008
6/24/2008
6/24/2008
6/19/2008
6/10/2008
6/3/2008
5/30/2008
4/22/2008
4/22/2008
4/22/2008
4/22/2008
4/22/2008
4/22/2008
4/22/2008
4/22/2008
4/2/2008
4/2/2008
3/6/2008
3/6/2008
9/28/2007
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
Yes
Yes
No
Yes
Yes
Fair
Fair
Fair
Fair
Fair
Fair
Fair
Fair
Fair
Dead
Dead
Fair
Fair
Fair
Fair
Fair
Fair
Fair
Dead
Fair
Fair
Fair
Fair
Fair
Dead
Dead
Fair
Fair
Fair
N=29
51
Figures
52
53
Figure 1. Location of artificial reef site FH-13 in the northern Gulf of Mexico
a.
b.
Figure 2. Pyramid structures used to construct artificial reef complexes at artificial
reef site FH-13 in the northern Gulf of Mexico (2a) and a trap that was used
for collecting fish during sampling (2b) (Photographs provided by the
Mississippi Department of Marine Resources).
54
X
XXX
X
Clump
100 ft
XX
X
XXX
X
100 ft
XX
Outlier 100 (OL100)
200 ft
XX
X
XXX
X
200 ft
XX
Outlier 200 (OL200)
300 ft
XX
X
XXX
X
300 ft
XX
Outlier 300 (OL300)
Figure 3. Artificial reef patterns deployed within each section of artificial reef site
FH-13 off the coast of Mississippi in the Gulf of Mexico.
55
2.5
Mean CPUE (Red snapper/h)
2
1.5
1
0.5
0
Clump
OL100
OL200
OL300
Figure 4. Mean catch per unit of effort (CPUE; red snapper/trap soak-hour) by
pattern with associated standard error bars for red snapper captured with
trap nets during September 2007 through November 2008 from artificial
reef site FH-13 off the coast of Mississippi in the Gulf of Mexico. The
clump pattern consists of five closely spaced pyramid structures, and the
outlier patterns consist of five closely spaced pyramids and two sets of two
outlier pyramids at 100 ft (OL100), 200 ft (OL200), and 300 ft (OL300)
from the main clump of pyramids.
56
2.5
Mean CPUE (Red snapper/h)
2
1.5
1
0.5
0
Spring
Summer
Fall
Figure 5. Mean catch per unit of effort (CPUE; red snapper/trap soak-hour) by
season with associated standard error bars for red snapper captured with
trap nets during September 2007 through November 2008 from artificial
reef site FH-13 off the coast of Mississippi in the Gulf of Mexico. Seasons
in which sampling took place were spring (March, April, and May),
summer (June, July, and August) and fall (September, October, and
November).
57
300
Mean total length (mm)
250
200
150
100
50
0
Clump
OL100
OL200
OL300
Figure 6. Mean total length (mm) by pattern with associated standard error bars for
red snapper captured with trap nets during September 2007 through
November 2008 from artificial reef site FH-13 off the coast of Mississippi
in the Gulf of Mexico. The clump pattern consists of five closely spaced
pyramid structures, and the outlier patterns consist of five closely spaced
pyramids and two sets of two outlier pyramids at 100 ft (OL100), 200 ft
(OL200), and 300 ft (OL300) from the main clump of pyramids.
58
300
Mean total length (mm)
250
200
150
100
50
0
Spring
Summer
Fall
Figure 7. Mean total length (mm) by season with associated standard error bars for
red snapper captured with trap nets during September 2007 through
November 2008 from artificial reef site FH-13 off the coast of Mississippi
in the Gulf of Mexico. Seasons in which sampling took place were spring
(March, April, and May), summer (June, July, and August) and fall
(September, October, and November).
59
Clump
Total Number Red Snapper
Total Number Red Snapper
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
Length Group (mm)
OL200
Length Group (mm)
Total Number Red Snapper
60
Total Number Red Snapper
Length Group (mm)
80
70
60
50
40
30
20
10
0
OL100
80
70
60
50
40
30
20
10
0
OL300
Length Group (mm)
Figure 8. Red snapper length frequency distributions by reef pattern type. Length measurements are total lengths (mm). Red
snapper were captured with trap nets during September 2007 through November 2008 from artificial reef site FH-13 off
the coast of Mississippi in the Gulf of Mexico. The clump pattern consists of five closely spaced pyramid structures,
and the outlier patterns consist of five closely spaced pyramids and two sets of two outlier pyramids at 100 ft (OL100),
200 ft (OL200), and 300 ft (OL300) from the main clump of pyramids.
Total Number Red Snapper
180
160
140
120
100
80
60
40
20
0
Spring
Total Number Red Snapper
Length Group (mm)
180
160
140
120
100
80
60
40
20
0
Summer
Total Number Red Snapper
Length Group (mm)
180
160
140
120
100
80
60
40
20
0
Fall
Length Group (mm)
Figure 9. Red snapper length frequency distributions by season. Length
measurements are total lengths (mm). Red snapper were captured with trap
nets during September 2007 through November 2008 from artificial reef
site FH-13 off the coast of Mississippi in the Gulf of Mexico. Seasons in
which sampling took place were spring (March, April, and May), summer
(June, July, and August) and fall (September, October, and November).
61
2.5
R² = 0.004
Loge CPUE (Red snapper/h)
2
1.5
1
0.5
0
Loge CPUE (Red snapper/h)
1
1.5
2
2.5
Square Root Dissolved Oxygen (mg/L)
2.5
3
R² = 0.006
2
1.5
1
0.5
0
31
32
33
34
Salinity (ppt)
35
Loge CPUE (Red snapper/h)
2.5
36
R² = 0.027
2
1.5
1
0.5
0
15
17
19
21
23
Temperature (Celsius)
25
27
29
Figure 10. Relationship between red snapper catch per unit of effort (CPUE; red
snapper/trap soak-hour) and environmental variables (dissolved oxygen,
salinity, and temperature) in the Mississippi artificial reef site
FH-13, Gulf of Mexico, from September 2007 through November 2008.
62
APPENDIX A
TOTAL NUMBER OF FISH BY SPECIES COLLECTED WITH TRAP NETS
FROM SEPTEMBER 2007 THROUGH NOVEMBER 2008 AT EACH
ARTIFICIAL REEF PATTERN WITHIN EACH SECTION OF
ARTIFICIAL REEF SITE FH-13 LOCATED OFFSHORE
OF MISSISSIPPI IN THE GULF OF MEXICO.
63
A
B
C
Species
Clump
OL100
OL200
OL300
Clump
OL100
OL200
OL300
Clump
OL100
OL200
OL300
Total
% of
Total
Lutjanus campechanus
116
71
61
112
60
122
77
60
83
69
77
19
927
66%
12
5
0
0
7
10
6
6
14
14
4
3
81
6%
0
1
0
0
0
0
0
0
0
0
0
0
1
< 1%
6
7
2
2
0
5
0
1
0
2
2
0
27
2%
0
0
0
0
1
0
0
0
0
0
0
0
1
< 1%
1
0
2
0
0
0
0
0
0
0
0
0
3
< 1%
28
52
17
22
1
9
1
0
0
4
3
2
139
10%
5
8
0
1
2
12
1
1
5
4
1
1
41
3%
5
3
0
0
1
4
0
0
2
0
2
0
17
1%
4
6
0
3
5
8
2
5
8
3
5
2
51
4%
Red snapper
Lutjanus synagris
Lane snapper
Lutjanus griseus
Gray snapper
Mycteroperca microlepis
Gag
64
Mycteroperca phenax
Scamp
Epinephelus nigritus
Warsaw grouper
Balistes capriscus
Gray triggerfish
Lagodon rhomboides
Pinfish
Haemulon aurolineatum
Tomtate
Centropritis philadelphica
Rock sea bass
Continued;
A
B
C
65
Species
Clump
OL100
OL200
OL300
Clump
OL100
OL200
OL300
Clump
OL100
OL200
OL300
Total
% of
Total
Micropogonias undulates
Atlantic croaker
2
0
0
0
16
3
11
12
2
0
0
1
47
3%
Equetus umbrosus
Cubbyu
1
0
0
0
4
0
0
0
1
1
0
1
8
< 1%
Orthopristis chrysoptera
Pigfish
14
12
0
4
0
3
0
1
0
2
1
0
37
3%
Rypticus maculates
Whitespotted soapfish
2
0
0
0
1
0
1
3
0
0
1
0
8
< 1%
0
0
0
0
1
1
0
0
0
0
0
0
2
< 1%
Carcharhinus limbatus
Blacktip shark
0
0
0
0
1
0
0
0
0
0
0
0
1
< 1%
Cynoscion arenarius
White trout
0
0
0
0
1
0
0
0
0
0
0
0
1
< 1%
Menticirrhus americanus
Southern kingfish
0
0
0
0
0
1
0
0
0
0
0
0
1
< 1%
Arius felis
Hardhead catfish
0
0
0
0
1
0
2
2
0
0
0
0
5
< 1%
Bagre marinus
Gafftopsail catfish
0
0
0
0
1
0
0
0
0
0
0
0
1
< 1%
Opsanus pardus
Leopard toadfish
0
0
0
0
0
1
0
1
1
0
0
0
3
< 1%
Total Number of Fish
196
165
82
144
103
179
101
92
116
99
96
29
1402
Rhizoprionodon
terraenovae
Atlantic sharpnose shark