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DIET AND CONDITION OF AMERICAN ALLIGATORS (Alligator mississippiensis)
INT THREE CENTRAL FLORIDA LAKES
AMANDA NICOLE RICE
A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
Amanda Nicole Rice
I am very grateful to Dr. J. Perran Ross who made it possible for me to be
involved in such an amazing project. Dr. Ross was always patient and provided
encouragement when needed. He taught me many things that will stay with me
throughout my career. My parents, John and LeeLonee Rice, graciously supported me
throughout my graduate work. Their support and earlier guidance gave me what I needed
to be successful. My other committee members, Dr. H. Franklin Percival and Dr. Mike S
Allen, both contributed to my success during my graduate work.
Many people helped me learn the necessary skills to handle this job. Notable
among them were P. Ross, Allan "Woody" Woodward, Chris Tubbs, Dwayne
Carbonneau, Arnold Brunnell, Chris Visscher, and John White. Woody Woodward was
especially helpful with understanding basic alligator ecology and with fieldwork. Field
techs C. Tubbs, Esther Langan, Rick Owen, Jeremy Olson, and Chad Rischar were
essential to the proj ect. Many great volunteers helped late into the night catching and
The Florida Museum of Natural History's (FLMNH) ornithology, mammology,
ichthyology, herpetology, and zoo archaeology collection managers and their reference
collections were invaluable with species identification. My lab assistants E Langan,
Anthony Reppas, and Patricia Gomez were all very helpful in painstakingly sorting
through the stomach samples. Richard Franz, Mark Robertson, Dr. Kenny Krisko,
Cameron Carter, Rob Robbins, Christa Zweig, Jamie Duberstein, and Hardin Waddle
were all valued contributors to this effort. Many friends and family members were also
supportive of me throughout my graduate career. The St. Johns River Water
Management District, Lakewatch Lab, and the Volusia County Environmental Lab
willingly shared their water quality data. The St. Johns River Water Management
District, Lake County Water Authority, Florida Fish and Wildlife Conservation
Commission, Florida Museum of Natural History and the Florida Cooperative Fish and
Wildlife Research Unit provided essential funding, facilities, and/or equipment for this
TABLE OF CONTENTS
ACKNOWLEDGMENT S ................. ................. iii...___ ....
LIST OF T ABLE S ........._.. ............ ............... vii...
LI ST OF FIGURE S .............. .................... ix
AB S TRAC T ......_ ................. ............_........x
1 INTRODUCTION ................. ...............1.......... ......
Study Site ................. ...............3.................
Obj ectives ................. ...............5.......... ......
2 HOSE-HEIMLICH TECHNIQUE ....._.. ................ ........____ ......... 1
Introducti on ................. ...............11..__.._.......
Method .....____................. ........____......... 1
R e sults................ ...............13........ ......
Discussion ................ ...............14........ ......
3 ALLIGATOR DIET AND CONDITION .............. ...............19....
Introducti on ................. ...............19..__.._.......
M ethods .............. ...............20....
Field M ethods ................. ...............20........ ......
Laboratory Methods .............. ...............20....
Gastric Digestive Rate ...._.. ................. ........____......... 2
Biomass of Fresh Prey ................. ...............23.......___....
Analy si s .................. .. ....... ...............24....
Quantitative diet analysis .............. ...............24....
Condition analysis ........ ................ ...............25.......
Diversity and equitability .............. ...............26....
Statistical analysis .............. ... ...............27...
Abnormal Lake Griffin alligators............... ...............2
R e sults............. _.. .... .._ ..... ...............29.
Alligator Diets among Lakes ...._ ......_____ ..... ...............29
Abnormal Lake Griffin alligators............... ...............3
Fi sh .................. ...............3.. 1..............
Other vertebrate prey groups............... ...............33.
Invertebrates ................ ...............36.................
Non-prey items .................. ...............37.................
Alligator Condition among Lakes .............. ...............37....
Discussion ................. ............. ...............39.......
Alligator Diets among Lakes ................ ...............39................
Variation among habitats .............. ...............40....
Fish .................. ...............42.................
Other vertebrate prey groups............... ...............45.
Invertebrates ................ ...............48.................
Non-prey items .................. ...............50.................
Alligator Condition among Lakes .............. ...............51....
4 CONCLU SION................ ..............8
LIST OF REFERENCES ................. ...............83........... ....
BIOGRAPHICAL SKETCH .............. ...............89....
LIST OF TABLES
1-1 Lake characteristics and water chemistry data ....._____ .... ... ..... ........_........6
2-1 Summary of methods used to obtain the stomach contents from crocodilians. .......17
3-1 Summary of methods used to estimate fresh mass for each prey group. .................57
3-2 Summary of samples among the lakes, including samples dropped, samples
containing fresh prey, samples containing no food items, and showing the
percentage of the samples containing fresh prey ......... ................. ...............57
3-3 Summary of method used to collect the stomach samples. ................ ................ ..58
3-4 Estimated total biomass of stomach content samples for alligators among the
lakes, including both vertebrate and invertebrate biomass and percentage of the
diet. .............. ...............58....
3-5 Lake Griffin alligator diet data including minimum number of individuals (mni),
percent occurrence, estimated mass in grams, and percentage of the diet for prey
group s and for taxa within prey group s ................ ...............59........... .
3-6 Lake Apopka alligator diet data including minimum number of individuals (mni),
percent occurrence, estimated mass in grams, and percentage of the diet for prey
group s and for taxa within prey group s ................ ...............62........... .
3-7 Lake Woodruff alligator diet data including minimum number of individuals
(mni), percent occurrence, estimated mass in grams, and percentage of the diet
for prey groups and for taxa within prey groups. .................. ................6
3-8 Shannon-Weiner diversity index (H') and Sheldon's equitability index (E)
results for alligator samples containing fresh prey............... ...............66..
3-9 Summary of abnormal Lake Griffin stomach content samples. .............. ..............66
3-10 Lake Griffin alligator shad consumption summary for this study. ..........................66
3-11 Shannon-Weiner diversity index (H') and Sheldon's equitability index (E)
results for alligator samples containing fresh fish ................. ........................66
3-12 Chi-square test of the occurrence of fish compared to the occurrence of other
prey (reptiles, mammals, birds, and amphibians) among the lakes..........................67
3-13 Frequency of occurrence for non-prey items among the lakes. ............. ................67
3-14 Condition analysis sample summary. .............. ...............68....
3-15 Alligator SVL and mass summaries from each study area. .................. ...............68
3-16 LSD post hoc test results comparing the mean condition among the lakes. ............68
3-17 Condition score range for all alligators divided into quartiles with assigned
ranks. ............. ...............68.....
3-18 Estimated alligator densities among the lakes............... ...............69.
LIST OF FIGURES
1-1 Location of study site, Lakes Griffin, Apopka, and Woodruff, in Florida. ........._.....7
1-2 Aerial photo of Lake Griffin, Lake County, Florida. ...........__.... ..._ ............8
1-3 Aerial photo of Lake Apopka, Lake and Orange Counties, Florida. ........................9
1-4 Aerial photo of Lake Woodruff and surrounding areas, Volusia County Florida....10
2-1 Hose-Heimlich technique on American alligator. ......___ ... ...... ..............18
3-1 Mean biomass (+SE) consumed by the alligators among lakes. .............. ...............70
3-2 Frequency of occurrence of prey groups for all prey in all samples for Lake
Griffin (n=85), Lake Apopka (n=44), and Lake Woodruff (n=46). ................... ......71
3-3 Frequency of occurrence of prey groups for samples containing fresh prey only
for Lake Griffin (n=63), Lake Apopka (n=33), and Lake Woodruff (n=3 5). ..........72
3-4 Percent composition by live mass for Lake Griffin alligators (N = 85)...................73
3-5 Percent composition by live mass for Lake Apopka alligators (N = 44). ................74
3-6 Percent composition by live mass for Lake Woodruff alligators (N = 46). .............75
3-7 Mean fish composition (+SE) for alligators among the lakes. ................ ...............76
3-8 Size (TL) of alligators sampled in this study divided into quartiles and
compared among the lakes. ............. ...............77.....
3-9 Estimated sizes (TL) of alligators observed during night light surveys from each
study area............... ...............78..
3-10 Mean condition (a SE) of alligators among lakes..........._.._.. ......._.._........._..79
3-11 Cumulative species recorded with increased sample size. ................... ...............80
Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science
DIET AND CONDITION OF AMERICAN ALLIGATORS (Alligator mississippiensis)
INT THREE CENTRAL FLORIDA LAKES
Amanda Nicole Rice
Chair: H. Franklin Percival
Major Department: Natural Resources and Environment
Understanding the diet of crocodilians is important because diet affects condition,
behavior, growth, and reproduction. By examining the diet of crocodilians, valuable
knowledge is gained about predator-prey interactions and prey utilization among habitats.
In this study, I examined the diet and condition of adult American alligators (Alligator
mississippiensis) in three central Florida lakes, Griffin, Apopka, and Woodruff. Two
hundred adult alligators were captured and lavaged from March through October 2001,
from April through October 2002, and from April through August 2003.
Alligators ate a variety of vertebrate and invertebrate prey, but vertebrates were
more abundant and fish dominated alligator diets in the lakes. Species composition of
Eish varied among the lakes. The majority of the diet of alligators from Lakes Apopka
and Woodruff was fish, 90% and 84% respectively. Lake Apopka alligators consumed a
significantly (P = 0.006) higher proportion of Esh in their diet. Fish were 54% of the diet
of Lake Griffin alligators and the infrequent occurrence of reptiles, mammals, birds, and
amphibians often resulted in a large biomass. Differences in alligator diets among lakes
may be due to differences in sample size (higher numbers of samples from Lake Griffin),
prey availability, habitat, prey vulnerability, or prey size.
Alligator condition (Fulton's Condition Factor, K) was significantly (P < 0.001)
different among the lakes. Alligators from Lake Apopka had the highest condition,
followed by those from Lake Griffin, and alligators from Lake Woodruff had the lowest
condition. Composition of Esh along with diversity and equitability of Esh in alligator
diets may have contributed to differences in condition among lakes. Condition was
probably also due to factors other than diet such as alligator hunting behavior, alligator
density, or year-round optimal temperature that prolongs feeding. The observed diet and
condition differences probably reflect both habitat differences and prey availability in
these three lakes.
Understanding the diet of crocodilians is important because diet affects condition,
behavior, growth, and reproduction (Chabreck 1972, Delany and Abercrombie 1986).
Many crocodilian food habits studies have been conducted (Fogarty and Albury 1968,
Chabreck 1972, Valentine et al. 1972, Taylor 1979, Webb et al. 1982, Delany and
Abercrombie 1986, Taylor 1986, Magnusson et al. 1987, Wolfe et al. 1987, Delany et al.
1988, Delany 1990, Platt et al. 1990, Webb et al. 1991, Thorbjarnarson 1993, Barr 1994,
Santos et al. 1996, Tucker et al. 1996, Barr 1997, Delany et al. 1999, Silveira and
Magnusson 1999, Platt et al. 2002, Pauwels et al. 2003). Diet explains much about
predator-prey interactions and prey utilization among habitats. This allows managers to
better assess the importance of crocodilians in the ecosystem. In this study, I compared
the diet and condition of adult American alligators (Alligator mississippiensis) among
populations from three central Florida lakes, Griffin, Apopka, and Woodrufff
American alligators inhabit fresh and brackish wetlands throughout their range in
the southeastern United States including all of Florida. American alligators are
considered a species of special concern in Florida, are listed federally as threatened due
to similarity of appearance because of their resemblance to the endangered American
crocodile (Crocodylus acutus), and are listed under CITES Appendix II (Ross 1998).
Condition analyses provide scientists with an easy mechanism to explore the
health of a species in its ecosystem (Murphy et al. 1990). Taylor (1979, p 349) defined
condition as "the relative fatness of the crocodile, or how much its food intake exceeds
that needed for homeostasis and growth....it is a measure of how well that animal is
coping with its environment." The various condition indices provide a numerical
condition score that is based on a skeletal length and a volumetric measurement (Zweig
2003). Crocodilian condition has been shown to vary among habitats and be associated
with crocodilian diets (Taylor 1979, Santos et al. 1994, Delany et al. 1999). In this study,
I compared condition of alligators among three lakes.
There is a need to assess and explore how crocodilian diets and condition vary in
lakes with different habitats because as lakes change over time the prey available to the
alligators changes, thus changing their diet. This modification in alligator diets may
affect and change their overall condition. Many of Florida's lakes have changed from a
macrophyte-dominated lake to a polluted algae-dominated lake (Fernald and Purdum
1998). These lake changes, which are mostly due to anthropogenic causes, affect the
predators and prey that occupy them.
In addition to the need to compare alligator diets and condition among habitats,
both Lakes Griffin and Apopka have experienced alligator mortality that is unexplained
(Woodward et al. 1993, Schoeb et al. 2002) and may or may not be related to their diet
and condition. Between 1997 and 2003, 442 sub-adult and adult alligators on Lake
Griffin died (D. Carbonneau, Florida Fish and Wildlife Conservation Commission,
personal communication). The cause for this alligator mortality has been investigated,
but no clear conclusions have emerged (Schoeb et al. 2002). Nutritional deficiencies,
specifically thiamine deficiencies, in alligator diets (i.e., alligator ingestion of fish with
high levels of thiaminase) were speculated as a cause and therefore an investigation of
alligator diets was warranted (Schoeb et al. 2002). Between 1980 and 1989 juvenile
alligator populations and clutch viability (number hatch/total eggs in a clutch) declined in
Lake Apopka and there were reports of adult alligator mortality on the lake as well
(Woodward et al. 1993, Rice 1996). The cause of this is also unknown but may have
been related to pesticides that entered the lake through agriculture, or a chemical spill of
the pesticide dicofol that occurred in 1980 near the southwest part of Lake Apopka
(Woodward et al. 1993). Dicofol contained DDT and, therefore, its impact on the system
and wildlife was a cause for concern (Rice 1996). Lake Woodruff has had little
agriculture and development associated with it and alligators on Lake Woodruff have had
a consistently high reproductive rate (Woodward et al. 1999), indicating that this system
is overall the healthiest of the three and therefore it was considered the reference lake in
this study. This study does not attempt to explore or determine the cause of the alligator
mortality on the lakes, but rather it will offer diet and condition data that may or may not
be associated or related to the problems.
Three central Florida lakes, Griffin, Apopka, and WoodruffNational Wildlife
Refuge (NWR) were chosen to compare the alligator diets and condition across
populations (Figure 1-1). Lake Griffin is located in Lake County, Florida (280 50' N, 81o
51' W) (Figure 1-2); Lake Apopka is located in Lake and Orange Counties, Florida (280
37' N, 81o 37' W) (Figure 1-3); and Lake Woodruff NWR is located in Volusia County,
Florida (290 06' N, 81o 25' W) (Figure 1-4). This study was conducted on Lake
Woodruff and the surrounding areas including Spring Garden Lake, Spring Garden canal,
Mud Lake, and the canal that connects Lake Woodruff to Mud Lake (Figure 1-4), which
are all part of the Lake Woodruff NWR.
Lakes Griffin and Apopka are hypereutrophic, alkaline, polymictic, shallow water
bodies and are a part of the Ocklawaha chain of lakes (Table 1-1). Throughout much of
the early 1900's both lakes were clear, macrophyte-dominated lakes known for their
excellent largemouth bass (M~icropterus salmoides) Eishing. However, between 1950 and
1970 both lakes dramatically changed due to water level controls, diking associated
marshes and runoff from urban areas, sewage, agriculture and citrus farming effluent.
Rapid trophic changes as well as pollution from organo-chemicals resulted.
Since the late 1990's both lakes experienced restoration efforts conducted by the
St. Johns River Water Management District (SJRWMD). External phosphorus loading
was reduced by elimination of farming on adjacent land (Fernald and Purdum 1998).
Both citrus farming, which ended in the mid-1980's due to several freezes, and muck
farming ended and marsh flow-way filtration systems were constructed. This wetland
filtration was designed to filter the lake water and remove suspended solids and
phosphorus. Lake water was circulated through a restored marsh on the former farms and
this is designed to filter the entire lake twice a year (Bachmann et al. 2001). Gizzard
shad were removed from the lake as a way to remove phosphorus and reduce
bioperturbation. Finally, macrophytes were planted in shallow areas to encourage game-
Eish habitat (Lowe et al. 2001).
Lake Woodruff NWR is a macrophyte-dominated, eutrophic, alkaline lake and is
part of the St. Johns River system (Table 1-1). Lake Woodruff has little human
development on its perimeter and has been affected far less from anthropogenic causes
compared to Lakes Griffin and Apopka.
One obj ective of this study was to investigate the hose-Heimlich technique for
accuracy and dependability in obtaining the stomach contents from live adult American
alligators. The main objective of this study was to analyze and compare the diet and
condition of adult American alligators across populations and among habitats.
Table 1-1. Lake characteristics and water chemistry data. Water quality data are given by means with + the standard deviation.
Mean Total Surface Open Water Total Total Chlorophyll a Secchi
Lake Depth (m) Area (ha) Surface Area (ha) Year pH Phosphorus (pg/1) Nitrogen (pg/1) (pg/1) Depth (m)
Griffin' 2.67 5742.2 3963.8 2001 8.7 77.6 & 21 4046 & 898 108 & 49.5 0.35 & 0.15
2002 8.5 57 & 16 3013 & 902 70 & 50.4 0.48 & 0.18
2003 8.8 50 & 7 2492 & 241 45 & 27 0.57 & 0.24
Apopka' 1.65 12960.2 12169.7 2001 8.9 152 & 19 5264 & 986 72 & 16 0.27 & 0.03
2002 8.9 190 & 48 6450 & 1427 86 & 25 0.25 & 0.04
2003 9.5 159 & 33 5071 & 677 86 & 22 0.29 & 0.02
WoodrufP2 1.84 6553.7 1269 2001 8.3 98 & 1 1470 & 116 32 & 14 1.55 & 0.21
2002 7.3 80 & 16 1341 + 176 22 & 19 2.1 & 0.38
2003 7.4 77 & 16 1160 & 138 4.8 & 4.3 0.83 & 0.15
1Data provided by St. Johns River Water Management District
'Data provided by Volusia County Environmental Lab
i~J;s4~a~ij~ r I N
: : ~~~ra~i
`s; ~iL: 1C ,r*
!L: ;I il*
.. ii ~*
25 37 N ~
a Ir 25 W
Figure 1-1. Location of study site, Lakes Griffin, Apopka, and Woodruff, in Florida.
1 1 In~lmi
Figure 1-2. Aerial photo of Lake Griffin, Lake County, Florida. Note extensive urban
development on the south and west sides. The dark area on the central east
side is the restored marsh on previous agriculture land.
Figure 1-3. Aerial photo of Lake Apopka, Lake and Orange Counties, Florida. The dark rectangular sections on the north side are
former agricultural land now reverted to restored marsh.
Figure 1-4. Aerial photo of Lake Woodn
settlement around the lakes.
-Ida. Notice the general absence
Animal diets can be studied by observing what it eats, feeding trials on captive
animals, biochemical and isotope analysis, or most simply by obtaining samples of the
ingested food from the stomachs of wild animals. Stomach contents can be obtained
post-mortem from specimens killed for that purpose or collected incidentally from
commercial harvests, and several alligator diet studies used stomachs from hunter
harvested alligators (Table 2-1). However, many crocodilian species are threatened or
endangered and there are ethical and practical constraints on killing animals for study.
Therefore, non-lethal methods have been developed to obtain stomach contents from live
animals without causing harm.
Non-lethal methods used to obtain the stomach contents fall into three categories:
invasive scoops that mechanically retrieve material through the esophagus (Taylor et al.
1978), irrigation methods that introduce water and flush material from the stomach
(Taylor et al. 1978) and combinations of the former two (Webb et al. 1982) (Table 2-1).
In this study, I used the hose-Heimlich technique (Fitzgerald 1989). My application of
this method is described in detail below and combined water flushing, gravity and
squeezing to expel the crocodilian stomach contents. This method was compared and
tested against other stomach flushing techniques and it was found to be less invasive than
the scoops and the most reliable (Fitzgerald 1989). The hose-Heimlich technique
removed 100% of the food items; however, a few of the subj ect animals retained some
rocks (Fitzgerald 1989). The hose-Heimlich technique is superior for obtaining the
stomach contents of live crocodilians and it was used in this study.
All of the stomach flushing methods caused minor irritations to the esophagus and
cardiac sphincter; however, no long-term effects have been observed (Fitzgerald 1989).
In some studies, the animals were held in captivity for several days or recaptured after
release and in both cases, the crocodilians showed no long lasting effects from the
stomach flushing procedures (Taylor et al. 1978, Webb et al. 1982, Fitzgerald 1989).
There are advantages and disadvantages to the stomach flushing techniques.
Although it provides the best results, the hose-Heimlich technique requires water under
pressure, while the various scoop and pump methods are more portable and do not
require water under pressure (Fitzgerald 1989). The hose-Heimlich technique has been
modified to be more portable by using a bilge pump or a gas-powered motor (Barr 1994,
1997). This allows researchers to lavage the crocodilian in the field where a domestic
water source may not be available. Considering that the hose-Heimlich technique can be
performed in the field, it was the method of choice because it provides the best results.
I first tested the accuracy and reliability of the hose-Heimlich technique on 20
alligators, which were lavaged and then examined at necropsy to determine the
proportion of contents recovered. In addition, we checked for any irritations to the
esophagus or stomach due to the insertion of the hose.
To perform the hose-Heimlich technique, the alligator was strapped to a 245 cm x
31 cm plywood board and placed at an incline, resting on a wood sawhorse. The jaws
were secured opened with a heavy-duty PVC pipe (200 mm length, between 60 and 150
mm diameter) of appropriate size. The soft Teflon hose of appropriate size (5 mm to 15
mm diameter) was coated with mineral oil and inserted into the esophagus and then into
the stomach of the alligator (Figure 2-1). An external marker indicating the posterior end
of the stomach (fourth whirl of scutes anterior to hind legs) allowed confirmation of
proper placement of the hose. The lavaging hose was connected to a garden hose, which
was connected to the water source. The water source was from a domestic water supply,
or from the lake using a 2839 liters per hour bilge pump or a 3.5 hp Briggs and Stratton
motor driven pump, and all provided around 50 liters per minute of water.
The alligator was then angled down with its mouth positioned over a 68-liter
bucket. With the water source running, the animal was squeezed in a 'Heimlich
maneuver' (Heimlich 1975) resulting in the expulsion of stomach content and water into
the bucket. This lavaging process was repeated until only clear water was entering the
bucket. The contents in the bucket were poured through a 0.5 mm mesh nylon strainer
and collected in 10% buffered formalin in 1L plastic j ars labeled with lake, date, and
identification numbers on each jar.
The hose-Heimlich technique (process described above) was an effective way to
obtain the stomach contents from live alligators. In 2001, this technique was tested on 20
alligators that were destined for euthanasia and necropsy. In all but one case, all contents
were obtained through this process with little ill effect on the alligators. Minor irritations
were observed on the alligator's esophagus and cardiac sphincter. In addition, during this
study we recaptured three alligators that had been previously lavaged. These alligators
appeared healthy with no ill effects from the hose-Heimlich technique.
During our initial testing, we observed one instance where the hose-Heimlich
technique was incomplete. During the necropsy, we found a large piece of gar
(Lepisosteus spp.) that was blocking the sphincter and not allowing water and contents to
exit the alligator. Therefore, an incomplete hose-Heimlich process was characterized by
low water and content output from the alligator and bloating of the stomach area making
it impossible to squeeze. During this study, an incomplete sample occurred four times
and on these rare occasions, the samples were not used in any of the diet analyses.
The hose-Heimlich technique was used as a portable method to obtain stomach
contents. The work up area at Lake Woodruff had no electricity or running water,
therefore, we used either a bilge pump (2839 liters per hour) or a gas powered motor (3.5
horse power) to obtain water under pressure. Both optional water sources worked as well
as water from a domestic water source.
The hose-Heimlich technique was most successful on alligators under 304 cm
total length (TL). Two separate attempts to lavage alligators 304 cm TL failed because of
insufficient power available to squeeze the alligator' s large abdominal area. The largest
alligator that was successfully lavaged was 290 cm TL. Therefore, the hose-Heimlich
technique was a reliable method to obtain stomach contents on live alligators < 290 cm
The hose-Heimlich technique has been used in several studies where it was a
successful way to obtain the stomach contents from live crocodilians (Fitzgerald 1989,
Barr 1994, 1997). This study also showed the reliability and effectiveness of the hose-
Heimlich technique. Fitzgerald (1989) tested the hose-Heimlich technique for
effectiveness on spectacled caiman (Caiman crocodilus) and found that it was the best
stomach flushing technique and it removed 100% of the caiman' s food content.
However, Fitzgerald (1989) did find that some caiman retained some stones in their
stomach. After evaluating this technique, we also found that there were times when
recovery of the stomach contents was incomplete. Some researchers did not evaluate the
effectiveness of the technique, and accepted Fitzgerald' s (1989) extensive evaluation of
the method (Barr 1994, 1997). However, by evaluating the technique I became
convinced in its effectiveness and was confident in using this technique to compare food
habits among lakes.
The hose-Heimlich technique did cause minor irritations to the alligator's
esophagus and cardiac sphincter. Fitzgerald (1989) evaluated any ill effects due to the
hose-Heimlich technique and found that only minor irritations to the esophagus occurred.
He concluded that these were not long lasting effects. We also found some abrasions on
the alligator' s esophagus and cardiac sphincter, but believe that these were minor and
temporary. Animals kept in captivity and those recaptured all appeared normal after
receiving the hose-Heimlich technique (Fitzgerald 1989, Barr 1997).
American alligators are a very abundant species of crocodilian and nine diet
studies obtained stomachs from harvested animals (Table 2-1). In addition to using the
hose-Heimlich technique to obtain stomach samples, I utilized stomachs from alligators
killed for other research. There was 100% reliability of obtaining all the stomach
contents when the alligators were killed. In addition, harvested alligators may be
preferable when investigating the diet of large alligators (i.e., > 290 cm TL). However,
there are non-lethal methods, such as the hose-Heimlich technique that offer a way to
reliably obtain the stomach contents from live alligators.
There are some disadvantages to using the hose-Heimlich technique in an
alligator food habit studies. Fitzgerald (1989) identified the need for water under
pressure as a disadvantage to the hose-Heimlich technique. However, by using a bilge
pump or gas powered motor, we adapted the method for use where a domestic water
source was unavailable. Barr (1997) also used a portable water pump to flush hundreds
of alligator stomachs. In addition, during this study the hose-Heimlich technique proved
to be most effective on alligators I 290 cm TL, therefore this technique may not be
effective to use on alligators > 290 cm TL. The largest caiman Fitzgerald (1989) tested
the hose-Heimlich technique on was 108 cm snout vent length (SVL) and the largest
alligator Barr (1997) used this technique on was 317 cm TL.
Table 2-1. Summary of methods used to obtain the stomach contents from crocodilians.
Method Crocodilian Size Range Reference
Harvest American alliao (4lligator inississippiensis) < 121 cm TL Fogat and Albur 1967
Harvest American alligao < 182 cm TL Chabreck 1972
Harvest American alligator 60 335 cm TL Valentine et al. 1972
Harvest American alligatr 220 cm (mean TL) McNease and Joanen 1977
Scoop and Pump Saltwater crocodile (Crocodulus porosus) < 180 cm TL Taylor 1979
Sopwith water method Freshwater crocodile (Crocodulus johnstoni) 16 122 cm TL Webb et al. 1982
Harvest American alligao 130 390 cm TL Delanv and Abercrombie 1986
Harvest American alligator 183 373 cm TL Taylor 1986
Scoop with water method Spectacled caiman (C'aiman crocodilus) 10 60 cm SVL Magnusson et al. 1987
Black caiman (M~elanosuchus niger)
Dwarf caiman (Paleosuchus palpebrosus)
Smooth fronted caiman (P. tionatus)
Harvest American alligator 150 300 cm Wolfe et al. 1987
Harvest American alligao 130 370 cm Delany et al. 1988
Harvest American alligator < 41 122 cm TL Delany 1990
Pupmethod American alligao 49 121 cm TL Platt et al. 1990
Sopwith water Saltwater crocodile (Crocodulus orosus) 30 120 cm TL Webb et al. 1991
Harvest Spectacled caiman (Caiman crocodilus) 20 90 cm SVL Thorbjamnarson 1993
Hose-Heimlich American alligao 82 122 cm TL Barr 1994
Scoop method Yacare caiman (Crocodulus vacare) < 50 cm > 70 cm SVL Santos et al. 1996
Sopand Pm Freshwater Crocodile 13 125 SVL Tucker et al. 1996
Hose-Heimlich American alligao < 38 cm 317 cm TL Barr 1997
Harvest American alligator 109 389 cm TL Delany et al. 1999
Sopwith water method Spetacled caiman (C'aiman crocodilus) 15 115 cm SVL Silveira and Manusson 1999
Pump method Morelet's crocodile (Crocodulus inoreletii) hatchlings Platt et al. 2002
Drowned animals Slender-snouted crocodile (Crocodulus cataphractus) 201 233 cm TL Paurvels et al. 2003
Figure 2-1. Hose-Heimlich technique on American alligator.
ALLIGATOR DIET AND CONDITION
Alligators are opportunistic and adaptive predators that occupy a variety of habitats
and exhibit a highly variable diet. Alligator diet studies have been concentrated in
Louisiana (Valentine et al. 1972, Taylor 1986, Wolfe et al. 1987, Platt et al. 1990), north
central and central Florida (Delany and Abercrombie 1986, Delany 1990, Delany et al.
1999), and southern Florida (Fogarty and Albury 1968, Barr 1994, 1997). All studies
supported the general conclusions that small alligators ate invertebrates and larger
animals ate more vertebrates, and that diet depended on prey availability and habitat.
Alligators in these three regions of the southeastern US exhibited different dominant prey
types, which reflected the different areas inhabited by the alligators and the prey
availability in those habitats (Delany and Abercrombie 1986, Wolfe et al. 1987, Barr
1997). In this study, I compared the diet of the alligators among three lakes.
Alligator condition was analyzed in this study in order to determine if condition
varies among habitats and across populations. Fulton's condition factor was used in this
study due to its ability to compare across populations. This condition index does have
some limitations, including the assumption of isometric growth and there are no
biological references for a "good" or a "bad" Fulton's condition score (Zweig 2003). In
addition, Fulton's K should only be used to compare animals of similar lengths (Cone
1989, Anderson and Neumann 1996). Zweig (2003) examined condition indices in
American alligators and concluded that Fulton's K was the best condition index to use
when comparing across populations.
Alligators were captured from lakes Griffin, Apopka, and Woodruff from March
through October 2001, from April through October 2002, and from April through August
2003. I sampled adult alligators that were captured from an airboat, between 2000 and
0400 hours, by a capture dart and snare. Each alligator was marked with two Monel self-
piercing tags (Natl. Band and Tag Co., Newport, Ky.) one in the third single dorsal scute
of the tail and one in the middle web of the right rear foot. The sex of each alligator was
determined by manual palpation. TL (tip of snout to tip of tail), SVL (tip of snout to
posterior end of cloaca), tail girth (TG circumference of the third whirl of scutes on the
tail from back legs), and head length (HL tip of snout to posterior end of scull) were
measured with a flexible tape to the nearest 0. 1 cm. Alligators were suspended in a
canvas sling and weighed to the nearest 2 kg using a spring scale.
Stomach samples were obtained within three hours of capture using the hose-
Heimlich technique (Fitzgerald 1989). Upon completion of the hose-Heimlich technique,
alligators were released at or near the site of capture. Additional stomach samples were
obtained during necropsy of alligators by other researchers. The stomach was removed
from the alligator and stomach contents were extracted, washed with water through a 0.5
mm mesh nylon strainer, and stored in 10% buffered formalin.
Alligator stomach content samples obtained in the field were taken to the
laboratory for analysis. Each sample was washed with water through a 0.5 mm mesh
nylon strainer and then preserved in 70% ethanol. Samples were sorted in the lab by
dividing the contents into major prey groups: Eish, reptiles, mammals, birds, amphibians,
gastropods, insects, crustaceans, or bivalves. Non-prey items were also divided up and
labeled as either: plant material, wood, rocks, sand, nematodes, artificial objects, or
other. Prey items were then identified to the lowest possible taxa by comparing them to
reference collections (preserved specimens and skeletal collections) of the Florida
Museum of Natural History (FLMNH). Minimum numbers of individuals were identified
based on the occurrence of specific items, e.g., occurrence of each atlas vertebrae
confirmed one specimen.
Gastric Digestive Rate
All prey items recovered in every stomach sample were categorized as either
freshly ingested (fresh) or not freshly ingested (old) (Barr 1994, 1997, Delany and
Abercrombie 1986). This process was very important to avoid over-representation of
indigestible prey because alligators are unable to digest chitin and keratin (Garnett 1985,
Magnusson et al. 1987). The following guidelines were established based on available
literature to categorize each prey item as either "fresh" or "old."
Fish. Fish digest very quickly in alligator stomachs (Delany and Abercrombie
1986); however, not all fish digest at the same rate and only shiners (Notemigonus
crysoleucas) were used in a digestive rate experiment by Barr (1994). Some fish may
have less digestible, thus more persistent, body parts (i.e., thick scales or spines). In this
study, Eish were considered fresh if anything of the fish remained, except for scales or
spines and old if only scales or spines remained.
Turtles. Turtle scutes, consisting of keratin, can persist in alligator stomachs, thus
over representing the occurrence and importance of turtles in alligator diets (Barr 1997,
Janes and Gutzke 2002). In this study, turtles were considered fresh if the turtle was
intact or if portions of bone remained along with scutes and the beak and old if only the
scutes and beak, or scutes alone remained.
Snakes. Snake scale, consisting of keratin, can persist in alligator stomachs (Barr
1997). In this study, a snake was considered freshly ingested if an intact body was found,
or some body sections along with vertebrae and scales were identified and old if only
Mammals. Mammal hair, consisting of keratin can persist in alligator stomachs
(Barr 1997). In this study, mammals found in the samples were considered fresh if large
pieces were recovered including the skull, vertebrae or long bones and hair and old if
only hair persisted in the sample.
Birds. Bird feathers, consisting of keratin can persist in alligator stomachs (Barr
1997). In this study, birds were considered fresh if large parts of the body were
recovered including long bones and feathers and old if only feathers were found in the
Amphibians. Frogs are possibly under-represented in an alligator diet study due to
their rapid digestibility (Barr 1997). In this study, any evidence of a frog in the sample
was considered fresh. No frogs identified were considered old. Aquatic salamanders
digest quickly in alligator stomachs (Delany and Abercrombie 1986). In this study, any
evidence of aquatic salamanders was considered fresh.
Gastropods. The opercula of freshwater snails contain chitin, which is
indigestible by alligators and therefore they can accumulate in alligator stomachs
(Garnett 1985, Barr 1994, 1997). In this study, snails with flesh attached and flesh
recently detached were considered fresh and samples containing opercula and shell pieces
only were old.
Bivalves. Freshwater mussels occurred in some samples; however, no digestive
rate studies have included bivalves. In this study, bivalves were treated similarly to
gastropods, meaning samples with flesh were considered fresh and samples with only the
shell were considered old.
Insects. An insect's exoskeleton contains chitin and is indigestible by alligators
(Garnett 1985). In this study, only intact insects were considered fresh and insects found
in pieces were considered old.
Crustaceans. Chelipeds from crayfish (Procamnbarus spp.) can remain in alligator
stomachs for over 108 hours (Barr 1997). In this study, only intact crustaceans (main
body cephalothorax and abdomen) were considered fresh. Evidence of crustaceans by
other parts of the body was considered old.
Biomass of Fresh Prey
Prey from the alligator stomach content samples identified as fresh were further
analyzed to estimate their live mass. This was accomplished in several ways. The
maj ority of live mass of the fresh prey was determined through allometric scaling. This
method was based on a linear measurement of a skeletal item (e.g., the atlas vertebrae) to
determine live fresh mass (Casteel 1974, Reitz et al. 1987, Brown and West 2000). This
included measuring a well preserved part of the prey (e.g., the skull or vertebrae) and
comparing it to the linear relationship to obtain both standard length and mass of the
Available field data were also used to determine live mass. The standard length of
the prey was first determined by comparison of the same preserved species in the
FLMNH. The average live mass of the same size prey was estimated from field data. In
some cases, the live mass was obtained directly from museum specimens that had weight
data. In addition, three reference books (Burt and Grossenheider 1980, Dunning 1993,
Hoyer and Canfield 1994) were used to estimate live mass by obtaining the average adult
mass for a specific species of prey. Fresh mass of invertebrates (except for the
Gastropods) was determined by directly weighing them to the nearest 0.01 g. The intact
invertebrates were stored in 70% ethanol for various lengths of time; therefore, this
estimation method represented their lowest possible mass due to the drying effects of
ethanol. Nevertheless, I decided that this was a close approximation to their live mass
and it was used in this analysis. Table 3-1 summarizes the biomass estimation methods
that were used for each prey group.
Quantitative diet analysis
The diet data were analyzed to detect differences in the diet of the alligators
among the lakes. Frequency of occurrence and percent composition by live mass were
used to quantitatively analyze the diet data (Bowen 1996). The equation for frequency of
where n = the number of stomach content samples containing a given food item and t =
the total number of stomach content samples. This analysis included all stomach content
samples and was applied to stomach content samples containing fresh prey as a
Percent composition by live mass utilized the estimated biomass data; therefore,
this analysis only included stomach content samples with fresh prey. Percent
composition by live mass was calculated by adding all the individual specimen biomass
estimations for a prey group and dividing that by the total biomass for the lake. This was
calculated for each prey group in all three lakes and this established the percentage of the
diet each prey group represented. Percent composition by live mass was also used to
calculate the percentage of the diet made up by each prey taxa within each lake. This was
calculated by dividing the prey taxa biomass by the total biomass for the lake.
The alligator diet data were expressed in a clear and meaningful manner by
categorizing all prey items as fresh or old, reporting frequency of occurrence for all
samples and samples containing only fresh prey items, and by reporting percent
composition by live mass. This recipe for analyzing crocodilian diets reported all the
data, while emphasizing an in depth analysis on fresh prey items. With this method,
over-representation of certain prey items was avoided, while the truly important prey
items were clearly identified and quantified.
A condition score was calculated for each alligator sampled to compare the
overall condition of alligators among lakes. The Fulton's Condition factor, K, (Zweig
2003) was used in this study to determine each alligator' s condition. The equation for K
K = W/L3 10n
where W = mass of the alligator in kg, L = SVL in cm, and n = 5. The range of condition
scores for alligators in all lakes was also divided into quartiles for a comparison and
assigned a rank. The mean condition score for the alligators in the lakes fell into one of
the following four ranks: low condition, low to average condition, average to high
condition, or high condition.
The condition of smaller alligators ranging in size from 182 to 304 cm TL from
all lakes was also compared because the proportion of alligators in each quartile was not
equally distributed among the lakes. This analysis was compared against the overall
condition analysis to see if the disproportionate sizes of the alligators caught among the
lakes affected the overall condition results.
Diversity and equitability
The Shannon-Wiener Diversity Index, H' (Krebs 1999) was used to compare the
diversity of alligator diets among the lakes. The formula for calculating the Shannon-
Wiener diversity index, H', was:
H' = C(Pi)(LNPi)
where s = the number of taxonomic categories, Pi = the proportion of samples of the ith
taxon and the natural log of the proportions was used (Krebs 1999).
Sheldon's Equitability Index, E (Ludwig and Reynolds 1988), was used to
determine if the alligators were consuming prey evenly and to compare it among lakes.
The formula for calculating the Sheldon's Equitability Index, E, was:
E = H'/LNs
where H' = the Shannon-Wiener Diversity Index, s = the number of taxonomic
categories, and the natural log was used in the analysis (Ludwig and Reynolds 1988).
The Shannon-Wiener Diversity Index and the Sheldon's Equitability Index were
calculated using the minimum number of taxa (MNT) identified in the stomach samples
for each lake. MNT included all prey identified to species level and also included prey
identified to genus or family when no other members were identified to a lower taxa in
the same group. For example, if the prey identified included Dorosoma spp., Dorosoma
cepedian2un, Leponsis spp., Centrarchidae, and Lepisosteus spp., the MNT would be
three. Dorosonza spp would be lumped with Dorosonza cepedianunt and Centrarchidae
would be lumped with Leponsis spp. The MNT method allowed us to avoid artificially
over representing the diversity of prey consumed (i.e., using all the taxa) and avoid under
representing the diversity of the prey consumed (i.e., lump by family groups). This
enabled us to clearly identify the diversity and equitability of prey consumed by the
alligators and this was applied to samples containing fresh prey, and samples containing
fresh fish. The diversity index ranges from zero to five and a greater diversity was
indicated by a score closer to five (Krebs 1999, Ludwig and Reynolds 1988). The
equitability index ranged from zero to one and a greater equitability of prey was indicated
with a score closer to one (Ludwig and Reynolds 1988)
All statistical analyses were performed using SPSS software (SPSS 2000). The
diet data did not meet the requirements of normality and homogeneity of variances;
therefore, non-parametric statistics were utilized. Three statistical tests were used on the
stomach content samples with fresh prey to identify any differences in the diet of
alligators among lakes.
A chi-square test was performed to compare the frequency of occurrence of fish
and other prey among the lakes. Mammals, birds, reptiles, and amphibians were lumped
together to form the other prey group due to low cell count. The Kruskal-Wallis analysis
of variance rank test was used to look for significant differences in the following two
tests. The mean biomass for the samples containing fresh prey was compared among
lakes. I hypothesized that the amount of prey consumed by the alligators would vary and
therefore the mean biomass consumed by the alligators would be different among lakes.
Percent composition of fish for each sample containing fresh prey was compared among
the lakes. Percent composition of fish was calculated as fish biomass/total sample
biomass 100. I hypothesized that the proportion of fish in the alligator diets would be
different and that alligators with the largest proportion of fish in their diet may also have
the highest condition. When significant differences were found among lakes using the
Kruskal-Wallis test, lakes were compared pair-wise using the Mann-Whitney U test.
Condition data were analyzed using parametric tests. The general linear model
was used to detect differences in the condition of alligators. The LSD post hoc test was
used to detect differences among lakes. Values for both diet and condition data were
expressed as the mean + one standard error unless otherwise indicated. Both diet and
condition statistical tests used an alpha of 0. 10, with the null hypothesis of no differences.
The alpha was set at 0.10 due to the low sample size and in an effort to avoid a Type II
error and increase the power in the analysis (Peterman 1990, Searcy-Bernal 1994).
Abnormal Lake Griffin alligators
Abnormal Lake Griffin alligators were sampled along with normal alligators during
2001. These alligators displayed neurological impairment (Schoeb et al. 2002) and these
samples were analyzed separately and not compared among the lakes. These samples
were analyzed in the same manner as the other samples, i.e., sorting to the lowest
possible taxa and minimum number of individuals, categorizing prey as fresh and old,
and estimating the fresh prey biomass. These samples will be reported and discussed
separately from normal alligator samples.
Alligator Diets among Lakes
American alligators ranging in size from 182 cm to 304 cm TL were captured
from lakes Griffin, Apopka, and Woodruff from March to October 2001, from April to
October 2002, and from April to August 2003. A total of 200 stomach content samples
were obtained from the three lakes (Table 3-2). Twenty-five samples were dropped from
the diet analyses because they were a recapture, an incomplete hose-Heimlich process
occurred (described in Chapter 2), or the alligator was considered abnormal. Abnormal
alligators were detected on Lake Griffin and were characterized as lethargic and
unresponsive to humans. These alligators were known to suffer a neurological
impairment of unknown causes (Schoeb et al. 2002), that might affect their feeding.
When a recapture occurred, the first sample was used in all analyses. One hundred and
thirty-seven of the 175 total stomach content samples for analysis were obtained from the
hose-Heimlich method (Table 3-3); and 38 stomach content samples were obtained
through alligator necropsies (Table 3-3).
Prey composition in the stomach samples varied greatly. Some samples contained
intact or partially digested fresh prey specimens, some samples contained old mostly
digested prey, some samples contained a combination of both, and some samples
contained no food items. The three samples that contained no food items (Table 3-2) did
contain non-prey items and therefore no empty stomachs were recovered in this study.
Most of the samples contained fresh prey (Table 3-2) indicating that the alligators were
eating frequently and the percent of stomach samples that contained fresh prey was
similar among lakes.
The prey biomass in the stomach samples also varied greatly. Some samples
contained a small number of fresh prey items and had small biomass, some samples
contained a single fresh prey item with large biomass, and some samples contained many
fresh prey items that together contributed a lot to biomass. The alligator diet biomass
ranged from 0.50 g to 4705 g among the lakes. This extensive range of prey mass found
in the alligator stomachs was evident in all the lakes. Lake Griffin alligators had the
highest mean biomass (mean = 594.4 & 95.9), followed by Lake Apopka alligators (mean
= 536.5 A 102. 1) and Lake Woodruff alligators had the lowest mean biomass (mean =
459.7 & 144.6) (Figure 3-1). No significant difference in the mean biomass were found
among the lakes (P = 0.103).
The alligators ate a wide variety of prey, including both vertebrates and
invertebrates. The majority of the prey consumed by the alligators was vertebrates.
Vertebrates occurred more frequently and made up a larger percentage of the biomass
than invertebrates (Table 3-4). The minimum number of fresh prey taxa identified in all
the samples was 83 (Tables 3-5, 3-6, 3-7). Lake Woodruff alligators had the highest
diversity and equitability of fresh prey and Lakes Apopka and Griffin alligators followed
this with equal fresh prey diversity (Table. 3-8). Lake Apopka alligator prey
consumption was a little higher in equitability than Lake Griffin alligator prey
consumption (Table 3-8). Lake Griffin alligators consumed the most prey taxa overall,
however, their diversity tied for the lowest. This low diversity for Lake Griffin alligators
was a result of an abundance of certain prey (e.g., apple snails, Pomacea paludosa and
grass shrimp, Palaemonetes intermedius) that affected the overall diversity results. The
equitability measure further exemplified this abundance of certain prey and revealed that
Lake Griffin alligators had the lowest equitability of fresh prey consumption among the
Abnormal Lake Griffin alligators
Thirteen abnormal alligators were samples from Lake Griffin during 2001 (Schoeb
et al. 2002) and they exhibited some similarities and some differences to normal Lake
Griffin alligator diets. Eight out of the 13 samples contained old food and most were
almost completely empty (Table 3-9). This large proportion of samples containing old
prey (62%) was higher than the amount of normal samples containing old prey, indicating
that abnormal alligators were not eating as frequently as the normal alligators or that
abnormal alligators had not eaten within a few days of capture. The fresh prey identified
in the samples included fish, reptiles and invertebrates, and this was similar to normal
samples. Two of the abnormal samples that contained fresh prey contained multiple
specimens of gizzard shad and many of the samples with old prey contained fish scales
that could not be identified beyond fish (Table 3-9). The consumption of shad among
normal Lake Griffin alligators in this study was minimal and this may have been due to a
shad removal by the SJRWMD in the spring of 2002 (Table 3-10).
Fish were the most important prey group in frequency of occurrence and in percent
composition by live mass for all lakes. Frequency of occurrence of fish was high for all
samples and the occurrence of fresh fish dropped only slightly (Figures 3-2, 3-3). Lake
Apopka alligators had the highest occurrence of fresh fish (64%), followed by Lake
Woodruff alligators (57%) and Lake Griffin alligators had the lowest occurrence of fresh
fish in their diet (44%) (Figure 3-3).
Fish represented the largest part of the diet in biomass for the alligators in the lakes.
Total Eish biomass for Lake Griffin alligators was 20,309 g or 54% of the diet (Figure 3-
4). Fish made up an overwhelming percentage of alligator diets from Lakes Apopka
(15,868.9 g or 90% of the diet) and Woodruff (13,586 g or 84% of the diet) (Figures 3-5,
3-6, respectively). While fish were the dominant prey in all lakes, the species
composition and number of Esh consumed varied among the lakes. Lake Griffin
alligators (Table 3-5) most commonly consumed catfish (Ictaluridae). Lake Apopka
alligators consumed a large number of shad (Clupeidae) (Table 3-6) and the largest
portion of fish consumed by the Lake Woodruff alligators was sunfish and bass
(Centrarchidae) (Table 3-7). Alligators from all lakes consumed gar (Lepisosteus spp.)
infrequently, but it had the potential to contribute a lot to biomass. For example, gar
occurred in 4.5% of the Lake Apopka samples and comprised 2826 g or 16% of the diet.
The diversity and equitability of Esh in alligator diets differed among the lakes.
The minimum number of fresh fish taxa consumed by the alligators in the lakes was 3 1
(Tables 3-5, 3-6, 3-7). Lake Woodruff alligators had the highest diversity and
equitability of fish in their diet, followed by Lake Griffin alligators, and Lake Apopka
alligators had the lowest diversity and equitability of fish in their diet (Table 3-11i). The
diversity and equitability of Lake Apopka alligator fish consumption stood out as much
lower and their minimum number of fish taxa consumed was also the lowest at seven
(Table 3-11). This difference may be due to habitat variations, meaning that Lake
Apopka alligators were possibly taking advantage of locally abundant prey (i.e., shad)
that were not available to the alligators in the other two lakes.
Percent composition of fish ranged from zero to 100%. Some samples contained
no fish, while other samples were comprised entirely of fish. Lake Apopka alligators had
the highest mean percent composition of fish in their diet (mean = 79.9% + 6.76),
followed by Lake Woodruff alligators (mean = 62.2% + 7.38) and Lake Griffin alligators
had the lowest mean percent composition of fish in their diet (mean = 48.5% + 6.05)
(Figure 3-7). There was a significant difference in the percent composition of fish among
the lakes (P = 0.006). Percent composition of fish for Lake Apopka alligators was higher
and significantly different from Lakes Griffin and Woodruff alligators (Mann-Whitney U
test: P = 0.002, P = 0.036, respectively). Percent composition of fish for Lakes Griffin
and Woodruff alligators was not significantly different (Mann-Whitney U test: P =
Other vertebrate prey groups
Other vertebrate prey groups (reptiles, mammals, birds, and amphibians) were less
important in the diet of alligators among the lakes. The occurrence of reptiles in all
samples for alligators from Lakes Griffin and Apopka was high (Figure 3-2), however,
this was due to the high incidence of turtle scutes and the occurrence dropped
dramatically when looking at only fresh reptiles (Figure 3-3). The occurrence of reptiles
in all samples for Lake Woodruff alligators was low (Figure 3-2) and also dropped when
looking at fresh reptiles (Figure 3-3). The occurrence of mammals, birds, and
amphibians were low for all samples among the lakes (Figure 3-2), and dropped slightly
for only fresh mammals, birds, and amphibians (Figure 3-3).
Lake Griffin alligators had the highest occurrence of other vertebrate prey groups.
This large occurrence of non-fish prey for Lake Griffin alligators was possibly due to the
larger sample size (Table 3-2). The chi-square test revealed differences in the diet of
alligators among the lakes (X2 = 7.64, df = 2, P = 0.02). The difference was largely due to
Lake Griffin alligator diets. Significantly fewer fish occurred than expected, while
significantly more other prey occurred than expected in Lake Griffin alligator diets
(Table 3-12). In addition, significantly less other prey occurred in the Lake Woodruff
alligator diets (Table 3-12). Lake Griffin alligator diets appeared to be different from
Lakes Apopka and Woodruff alligator diets, due to the greater occurrence of non-fish
prey and the lower occurrence of fish in Lake Griffin alligator diets.
The biomass for other vertebrate prey groups was highly variable and these
infrequent non-fish prey items had the potential to comprise a lot in biomass. The large
infrequent prey items were most commonly mammals and birds and were more frequent
in Lake Griffin alligators. Two mammal specimens, a raccoon (Procyon lotor) and a
hispid cotton rat (Sigmodon hispidus) together made up 4,860 g or 13% of the diet for
Lake Griffin alligators (Table 3-5, Figure 3-4). In addition, four bird specimens made up
5,763 g or 15% of the diet for Lake Griffin alligators (Table 3-5, Figure 3-4).
Mammals and birds comprised a less significant portion of alligator diets from
Lakes Apopka and Woodruff, therefore, the occurrence of a large infrequent prey item
was less. Lake Apopka alligators consumed two mammals (Table 3-6), representing only
33 1 g or 2% of the diet (Figure 3-5). One Lake Apopka alligator ate an anhinga (Anhinga
anhinga), which had an estimated weight of 1,235 g or 7% the diet (Figure 3-5). A single
round-tailed muskrat (Neofiber alleni) (Table 3-7) was identified from Lake Woodruff
samples and the estimated mass of this mammal was 289 g or 1.8% of the diet (Figure 3-
6). No fresh birds were identified in any Lake Woodruff samples.
Reptiles were the most commonly consumed non-fish vertebrate prey and were
most frequently consumed by Lake Griffin alligators. The most common reptiles
consumed by alligators were turtles, specifically the stinkpot turtle (.Slillinotheins/
odoratus). Alligators in all the lakes also consumed aquatic snakes and there was
evidence of alligators. None of the alligators consumed in this study were considered
fresh prey items and they were all represented by FWC hatchling tags that had remained
in the stomach for an unknown amount of time. Alligator eggshells were found in two
Lake Griffin alligator samples (one female and one male alligator) and in one Lake
Woodruff alligator sample (female alligator).
Reptiles, specifically turtles had the potential to be a large prey items and one Lake
Griffin alligator ate a redbelly turtle (Pseudemys nelsoni) estimated at 1148 g. Lake
Griffin alligators ate reptiles more frequently and these reptiles totaled 3,755 g or 10% of
the diet (Figure 3-4). Reptiles comprised a smaller portion of alligator diets for Lakes
Apopka (158 g or 1.6% of the diet) and Woodruff (108 or 0.6% of the diet) (Figs. 3-5, 3-
6, respectively). Three gopher tortoises (Gopherus polyphemus), a terrestrial species,
were consumed by alligators. Lake Griffin alligators consumed two gopher tortoises
(Table 3-5) and a Lake Apopka alligator consumed one gopher tortoise (Table 3-6).
Amphibians were not a significant portion of the alligator diets from any lakes, but
large species (e.g., Rana catesbiana, Siren lacertina) had the potential to be a large meal.
Amphibians consumed by the alligators included frogs and aquatics salamanders (sirens
and amphiumas). Lake Griffin alligators consumed the greatest number of amphibian
taxa (3) and the greatest number of amphibian specimens (5) (Table 3-5). The total
amphibian biomass for Lake Griffin alligators was 1,374.4 g or 4% of the diet (Figure 3-
4). No amphibians were identified in any Lake Apopka samples. Lake Woodruff
alligators consumed two greater sirens (Siren lacertina) that totaled 1,325 g or 8% of the
diet in biomass (Figure 3-6). One of these sirens was 1000 g (Table 3-7).
Invertebrates were not a significant part of alligator diets based on both frequency
of occurrence and percent composition by live mass. Invertebrates included gastropods,
insects, crustaceans, and bivalves. The occurrence of invertebrates in all samples was
high among the lakes, however, the occurrence dropped dramatically for fresh
invertebrates. For example, the occurrence of gastropods consumed by Lake Griffin and
Lake Woodruff alligators was 74% and 89%, respectively for all samples, however, the
occurrence of fresh gastropods dropped to 28% and 41%, respectively (Figures 3-2, 3-3).
In addition, the occurrence of insects consumed by Lake Apopka alligators was 61% for
all samples, however, the occurrence of fresh insects dropped to 9% (Figures 3-2, 3-3).
This drop in invertebrate occurrence was due to the accumulation of indigestible
invertebrate parts made of chitin in alligator stomachs, which were discarded during fresh
Fresh invertebrates were a small proportion of biomass for alligators in all the
lakes. The only invertebrate that contributed significantly in biomass was the apple snail.
Lake Griffin alligators ate 941 apple snails, however, only 64 of those were considered
fresh (Table 3-5). Total fresh apple snail biomass for Lake Griffin alligators was 1,321.9
g or 4% of the diet (Figure 3-4). Thirty out of the 303 apple snails consumed by Lake
Woodruff alligators were fresh and these 30 apple snails (along with two small banded
mystersnails, Viviparus georgian2us) made up 695.4 g or 4% of the diet (Table 3 -7, Figure
3-6). Both Lake Griffin and Lake Woodruff alligators consumed freshwater mussels,
Utterbachia spp. (Tables 3-5, 3-7). Insects and crustaceans only comprised trace
amounts of biomass for alligators among the lakes (Figures 3-4, 3-5, 3-6).
Non-prey items were commonly found in alligator stomachs. Non-prey items were
analyzed by frequency of occurrence (Table 3-13). Plant material (aquatic vegetation,
seeds, and nuts) was commonly found in alligator stomachs among the lakes. Wood was
also commonly found in alligator stomachs among the lakes. Rocks were more common
in Lake Apopka alligator stomachs and were least commonly found in Lake Woodruff
alligator stomachs. Sand was found in Lakes Griffin and Apopka alligator stomachs, but
not in Lake Woodruff samples.
Nematodes were found in almost every sample among the lakes. Nematodes from
ten samples were analyzed to identify species and this resulted in the identification of
three nematode species. The three nematodes identified were: Dujardina~scaris waltoni,
Brevimulticaecum tenuicolle, and Ortleppa~scaris antipini. Artificial objects were
identified in many of the samples and these included toys, golf balls, fishing lures and
hooks, shot gun shells, a lighter, spark plugs, and glass.
Alligator Condition among Lakes
Alligator condition, a measure of relative fatness was compared among the lakes.
Forty-four samples out of 200 were dropped from the condition analysis due to lack of
measurement data, recaptures, or the animal was categorized as abnormal by the field
biologist (Table 3-14). l used SVL and mass data (Table 3-15) in the Fulton's condition
factor, K, to obtain a condition score for each alligator.
Alligator condition scores from lakes Griffin, Apopka, and Woodruff ranged from
1.69 to 4. 13 and differed significantly among the lakes. Lake Apopka alligators were
clearly bigger and heavier in comparison to the alligators from the other two lakes. Lake
Woodruff alligators had the lowest condition scores among the lakes and appeared the
skinniest of them all. Lake Griffin animals on average were intermediate in size and their
mean condition score ranged between Lakes Apopka and Woodruff alligators.
Alligators compared in the condition analysis ranged from 182 to 304 cm TL;
however, a comparison of size class by quartile revealed that the proportion of alligators
in each quartile was not equally distributed among the lakes (Figure 3-18). A larger
proportion of smaller Lake Woodruff alligators were captured compared to smaller size
alligators caught from Lakes Griffin and Apopka. Larger alligators were generally hard
to catch on all three lakes, but the capture of large Lake Woodruff alligators posed an
even greater challenge. Data collected during night light surveys on the three lakes (A.
R. Woodward, Florida Fish and Wildlife Conservation Commission unpublished data)
revealed a greater proportion of smaller alligators on Lake Woodruff compared to Lakes
Griffin and Apopka; however, the proportion captured in this study does not exactly
correspond with the estimated natural population (Figure 3-9).
The K for all Lake Griffin alligators ranged from 1.63 to 3.70 (mean = 2.66 &
0.045), while the K for all Lake Apopka alligators ranged from 2.15 to 4.13 (mean = 2.99
& 0.059) and the K for all Lake Woodruff alligators ranged from 1.86 to 3.08 (mean =
2.48 & 0.041) (Figure 3-10). The mean Fulton's K score for the lakes was significantly
different (P < 0.001). The LSD post hoc test revealed that the condition of the alligators
among the lakes was significantly different (Table 3-16). The comparison of smaller
alligators (182 213 cm TL) also showed that there was a significant difference in the
mean alligator condition among the lakes (P < 0.001). The LSD post hoc test also
revealed that the condition of these smaller alligators among the lakes was significantly
different and therefore the disproportionate sizes of alligators sampled did not affect the
overall condition results.
The range of condition scores for all alligators (1.69 4. 13) was divided up into
quartiles and assigned a rank because Fulton's K does not have biological standards for a
"low" or a "high" condition score (Table 3-17). Alligators from Lakes Griffin and
Woodruff were both categorized as having a low to average condition; however, the Lake
Woodruff alligators were at the bottom of this range and the Lake Griffin alligators were
at the top of this range. Lake Apopka alligators fell into the fourth quartile and were
categorized as having a high condition. The condition of the Lake Apopka alligators
stood out as much higher (i.e., relatively more robust) than alligators from the other two
lakes even though they were all significantly different.
Alligator Diets among Lakes
American alligators in this study consumed a wide variety of prey and this was
consistent with other adult alligator diet studies (Delany and Abercrombie 1986, Delany
et al. 1988, Delany et al. 1999, Wolfe et al. 1987). Diverse diets may be due to habitat
type, local prey abundance, prey vulnerability, and prey size. The prey composition and
prey biomass in alligator stomach samples in this study varied greatly. This variety
included samples containing fresh intact or partially digested prey, samples containing
old mostly digested prey, or a combination of both. However, most of the samples did
contain fresh prey indicating that the alligators were eating frequently. The number of
specimens and estimated biomass of the fresh prey also varied greatly. For example, one
sample contained six small fresh prey specimens, which was estimated at 80 g in
biomass. While another sample contained one large fresh prey item that was estimated at
4705 g. This diversity of prey composition and prey weight in the stomach samples
occurred in other adult alligator diet studies (Delany and Abercrombie 1986, Delany et al.
1988, Delany et al. 1999, Wolfe et al. 1987, Barr 1997).
Adult crocodilians mostly consumed vertebrates and depending on habitat type,
repeatedly consumed certain prey types (Delany and Abercrombie 1986, Magnusson et
al. 1987, Thorbjarnarson 1993, Barr 1997, Delany et al. 1999). The majority of prey
consumed by the alligators in this study was vertebrates. These adult alligators did
consume invertebrates; however, fresh invertebrates did not occur often and did not
contribute significantly in biomass. The alligators in this study repeatedly ate certain
prey items (e.g., fish, stinkpot turtles, and apple snails) and this may be due to prey
abundance, habitat type, or ease of capture.
Variation among habitats
Habitat, prey availability, and prey abundance play a huge role in alligator diets.
Alligators inhabit a variety of water systems including freshwater lakes, coastal marshes,
rivers, swamps and ponds. These areas can have different trophic levels (freshwater
systems), different prey available, and different prey abundance, which all affect alligator
diets because alligators are opportunistic predators. In this study, Lakes Griffin and
Apopka have similar characteristics of being algae-dominated, hypereutrophic systems,
while Lake Woodruff is a macrophyte-dominated, eutrophic lake. Lakes Griffin and
Apopka were once macrophyte-dominated, game fishing lakes with clear water, however,
due to many factors (e.g., hurricane winds, point source pollution, and agriculture runoff)
throughout the last six decades the lakes have changed (Canfield et al. 2000, Bachmann
et al. 2001). As lakes change either through eutrophication or through restoration, the
Eish community within a lake will also change (Bachmann et al. 1996). Many game fish
(e.g., largemouth bass) require aquatic macrophytes to survive and when the macrophytes
are eliminated, the game fish population will also be eliminated, thus changing the fish
community (Canfield et al. 2000). Gizzard shad become much more productive in lakes
with increasing chlorophyll a levels and shad often become the dominate fish species in
hypereutrophic lake systems (Bachmann et al. 1996, Allen et al. 2000). Managers need
to be aware that changes in lakes due to either trophic state changes or restoration will
affect the fish community. Because alligators are opportunistic and adaptable animals,
their diet will also change.
Adult alligators inhabiting Florida have a different diet from alligators inhabiting
Louisiana, due to the different habitats that support different prey. Adult alligators in
north central and central Florida predominantly ate fish (Delany and Abercrombie 1986,
Delany et al. 1999), while, adult alligators in Louisiana predominantly ate mammals
(Valentine et al. 1972, McNease and Joanen 1977, Taylor 1986, Wolfe et al. 1987).
Nutria (M~yoca~stor coypus), an aquatic rodent, inhabit Louisiana wetlands and were an
abundant prey item for the alligators there. Nutria did not occur on my study lakes.
Apple snails were common prey items for alligators of all sizes in Florida (Fogarty and
Albury 1967, Delany and Abercrombie 1986, Delany et al. 1988, Barr 1994, 1997,
Delany et al. 1999), but do not occur in Louisiana and therefore were not available to the
alligators there. Louisiana alligators consumed more crustaceans and insects instead of
apple snails (Valentine et al. 1972, McNease and Joanen 1977, Wolfe et al. 1987).
Sub-adult alligators inhabiting different habitat types within Louisiana had different
diets (Chabreck 1972). Chabreck (1972) sampled 10 sub-adult alligators from a
freshwater environment and 10 sub-adult alligators from a saline environment. The
alligators from both habitat types consumed crustaceans the most, however, the species
composition of crustaceans varied between the habitat types. The freshwater inhabitants
ate more vertebrates and crawfish (Procamnbarus clarki), while the saline inhabitants ate
more blue crabs (Callinectes sapidus) (Chabreck 1972).
Within Florida, there were distinct differences in the diet of adult alligators. Fish
dominated the diet of alligators from north central and central Florida (Delany and
Abercrombie 1986, Delaney et al. 1999), whereas reptiles and amphibians dominated the
diet of alligators in the Everglades (Barr 1997). Even more specifically the diets differed
among lakes in this study. Fish dominated the alligators diet among lakes; however, the
species composition and number of fish specimens differed greatly. This may be due to
trophic lake differences, habitat differences, differences in local prey abundance, or
overall differences in prey availability.
Fish are an important prey group for many adult crocodilian species, including the
American alligator (Delany and Abercrombie 1986, Thorbjarnarson 1993, Santos et al.
1996, Delany et al. 1999, Silveira and Magnusson 1999). Fish were the dominant prey
group for adult alligators (180 300 cm TL) in Florida, except for alligators in the
Everglades (Delany and Abercrombie 1986, Barr 1997, Delany et al. 1999). In this
study, fresh fish had the highest occurrence and the highest percent composition by live
mass for all prey groups for the alligators among the lakes.
Fish dominated the diet of the alligators among the lakes, but fish were especially
important in alligator diets from Lakes Apopka and Woodruff compared to the Lake
Griffin alligator fish consumption. This similarity of a dominant fish diet from Lakes
Apopka and Woodruff alligators may be due to the similar sample size for those lakes.
The sample size for Lake Griffin alligators was almost twice as large as the sample size
for Lakes Apopka and Woodruff(Table 3-2), thus providing an accumulation of more
prey species and specimens (Figure 3-11). Lake Griffin alligators were sampled more
and therefore there were more species identified in their samples, and there was a greater
chance to find the infrequent large prey item in their diet. This may explain the
difference in the fish dominance between Lake Griffin alligators and alligators from
Lakes Apopka and Woodrufff
Although fish dominated the diet of the alligators in all the lakes, species
composition and diversity and equitability of fish consumed by the alligators were
different. All alligators ate some same fish species (e.g., gizzard shad, catfish, gar, and
black crappie); however, the dominant species consumed differed among the lakes. Lake
Griffin alligators consumed the second highest diversity of fish and consumed mostly
catfish. This high diversity could be due to the larger sample size obtained for Lake
Griffin alligators. Lake Apopka alligators consumed mostly shad, which were gizzard
shad (Dorosoma cepedianum) and small gizzard shad or threadfin shad (Dorosoma
petenense). Lake Apopka alligators had the lowest diversity and equitability in their fish
consumption. Lake Woodruff alligators consumed mostly sunfish and bass and had the
highest diversity and equitability in their fish consumption. These differences may be
due to different habitats occupied by the alligators in this study, which will be explored
Other adult alligator studies in Florida have shown that a lake's trophic state may
play a role in alligator diets and therefore alligators from different lakes with similar
trophic states may exhibit similar diets and alligators from different lakes with different
trophic states may exhibit different diets. Delany and Abercrombie (1986) found no
significant differences in the diet of alligators among three lakes in north central Florida
that were all considered eutrophic. However, Delany et al. (1999) found that alligator
fish consumption differed among lakes with different trophic states. Fish were more
dominant in the diet of alligators from lakes with higher chlorophyll a concentrations
(Delany et al. 1999). Fish densities increase with an increase in concentrations of lake
total phosphorus, total nitrogen, and chlorophyll a and with decreasing Sechhi depth (i.e.,
increasing trophic state) (Bachmann et al. 1996). Therefore, alligators occupying lakes
with a higher trophic state would inhabit a lake system with the greatest fish density. In
this study, both Lakes Griffin and Apopka are hypereutrophic, algae-dominated lakes and
Lake Woodruff is a eutrophic, macrophyte-dominated lake. However, fish
overwhelmingly dominated alligator diets from Lakes Apopka and Woodruff, suggesting
that trophic state alone may not predict fish consumption by alligators.
A few factors may have contributed to this difference in fish dominance in the diet
compared to trophic state. Lake Griffin is a hypereutrophic lake; however, the SJRWMD
removed one million pounds of gizzard shad and 25,000 pounds of gar in the spring of
2002 as part of their restoration efforts, just prior to our alligator sampling. This shad
removal altered fish populations in the lake (personal observation) and, thus, availability
to alligators. Along with this, the larger sample size for Lake Griffin alligators allowed
for a greater chance to encounter a large infrequent non-fish prey item. Lake Apopka is a
hypereutrophic lake and alligators there had a significantly larger proportion of fish in
their diet compared to the other two lakes. Lake Apopka alligators ate mostly shad, which
do increase in density with increasing trophic state (Bachmann et al. 1996). Lake
Woodruff is a eutrophic lake and alligators there had a high diversity and equitability of
fish in their diets. These Lake Woodruff alligators did have an overwhelming part of
their diet from fish, however it did not compare to the proportion of fish in the Lake
Apopka alligators diet. Lake Woodruff alligators did consume fish often, but they also
often consumed invertebrates such as apple snail, possibly a part of the difference.
The consumption of fish with high levels of thiaminase causing depressed thiamin
in alligators was one hypothesis for the cause of the Lake Griffin alligator mortality (P.
Ross, FLMNH, personal communication). Gizzard shad in Lakes Griffin and Apopka
had high levels of thiaminase (P. Ross, FLMNH, unpublished data); however, the
alligators from Lake Griffin did not eat many shad during this study (Table 3-10). Lake
Apopka alligators did eat large amounts of shad during this study (Table 3-6); however,
there was not a case of adult mortality on that lake during this study. The SJRWMD
removal of shad in 2002 on Lake Griffin may have affected this result of only one shad
found in the Lake Griffin alligator diets after 2001 (Table 3-10). A dietary cause to the
alligator mortality of Lake Griffin needs to be explored further and cannot be determined
based on this study.
Other vertebrate prey groups
Other vertebrate prey groups (reptiles, mammals, birds, and amphibians) were less
important in alligator diets among the lakes in both frequency of occurrence and in
percent composition by live mass. The occurrence of non-fish prey occurred
significantly more in Lake Griffin alligator diets. These non-fish vertebrate prey items in
Lake Griffin alligator diets tended to be large and comprised a lot in biomass. For
example, one Lake Griffin alligator ate one raccoon (Procyon lotor) that was estimated at
4705 g. The large and infrequent prey item occurred in alligator diets from Lakes
Apopka and Woodruff, but less frequently. Other studies have mentioned the occurrence
of a large prey item in crocodilian diets that comprised a lot in weight (Wolfe et al. 1987,
Webb et al. 1991). Wolfe et al. (1987) reported that alligators in Louisiana frequently ate
both nutria (M~yoca~stor coypus) and muskrat (Ondatra zibethicus) comprising over 83%
of alligator diets. Webb et al. (1991) reported that juvenile saltwater crocodiles
(Crocodylus porosus) in the Northern Territory of Australia consumed large rats (Rattus
colletti) infrequently, but they contributed a large portion of mass. If prey are equally
available and vulnerable then alligators should take the largest possible prey item to
maximize feeding efficiency (Wolfe et al. 1987).
Reptiles were the most frequently eaten non-fish prey item among the alligators,
especially with Lake Griffin alligators. Most reptiles consumed by alligators were turtles,
but snakes and American alligators were consumed also. Evidence of cannibalism was
found in this study, and cannibalism has been reported in other alligator diet studies
(Valentine et al. 1972, McNease and Joanen 1977, Delany and Abercrombie 1986,
Delany et al. 1988, Barr 1997, Delany et al. 1999). Reptiles were also an important prey
group for alligators in other Florida diet studies (Delany and Abercrombie 1986, Barr
1997, Delany et al. 1999). Delany and Abercrombie (1986) found that reptiles,
specifically turtles, occurred second after fish in dominance for alligators 200 300 cm
TL and that reptiles were the most important prey group for alligator > 300 cm TL.
Reptiles were not an important prey group for adult alligators in Louisiana (Valentine et
al. 1972, Wolfe et al. 1987). Wolfe et al. (1987) reported that snakes occurred more and
comprised greater mass than turtles, but overall reptiles comprised only 3% of alligator
diets. The most frequently eaten reptile in Louisianan was the cottonmouth (Agkistrodon
piscivorus) (Wolfe et al. 1987). Reptiles were an important prey group for adult
Everglades alligators, where snakes were the most prevalent, followed by turtles (Barr
1997). Reptile occurrence and importance in adult alligator diets are highly variable and
depend on habitat type, prey availability and size of the alligators.
The occurrence of terrestrial gopher tortoises (Gopherus polyphemus) was
unexpected. Nevertheless, they were found in three alligators from two lakes and they
were estimated to be an adult, a sub-adult, and a juvenile. Gopher tortoises may be taken
at the waters edge, after being washed into the lake, or as a result of the disposal of
carcasses illegally caught by people.
Alligator eggshells were recovered in some alligator stomachs in this study and
have been recovered in other crocodilian diet studies (McNease and Joanen 1977, Delany
and Abercrombie 1986, Wolfe et al. 1987). In this study, three alligators (one male and
two females) had alligator eggshells in their stomachs. Female alligators are known to
open their hatchling eggs by carefully crushing them in their jaws and then releasing the
hatchlings in the water. Kushlan and Simon (1981) observed female alligators aiding the
release of her hatchlings and observed the female ingesting infertile eggs. The female
alligator may be ingesting nutrients from the infertile egg and this may explain the
occurrence of alligator eggshells in the stomachs (Kushlan and Simon 1981). One of the
alligators with eggshells in its stomach was a male alligator and in this case, the male
may have eaten the eggshells post hatching.
Amphibians have been shown to be an insignificant part of alligator diets
throughout its range, except for the Everglades alligators (Valentine et al. 1972, McNease
and Joanen 1977, Delany and Abercrombie 1986, Taylor 1986, Wolfe et al. 1987, Delany
et al. 1988, Tucker et al. 1996, Barr 1997). Everglades alligators consumed larger
aquatic salamanders (sirens and amphiumas) frequently and this was the highest recorded
amphibian consumption by alligators (Barr 1997). Amphibians, especially frogs, digest
quickly in alligator stomachs (Delany and Abercrombie 1986, Barr 1997) and therefore
some studies may not sample frequently enough to detect amphibians in alligator
stomachs. In this study, Lake Griffin alligators consumed one greater siren (Siren
lacertina), one two-toed amphiuma (Amphiuma means) and three frog specimens (Rana
spp. ) and Lake Woodruff alligators consumed two greater sirens. Frogs are an abundant
amphibian species that are densely populated throughout the alligator's range. However,
frogs were rarely reported as alligator prey and if they were reported their occurrence was
low, indicating their unimportance in alligator diets (Valentine et al. 1972, McNease and
Joanen 1977, Delany and Abercrombie 1986, Taylor 1986, Wolfe et al. 1987, Delany et
al. 1988, Platt et al. 1990, Barr 1994, Tucker et al. 1996, Barr 1997, Delany et al. 1999).
Amphibians may not be an important prey group for alligators (except in the Everglades)
or more frequent sampling resulting in a larger sample size may be needed to detect their
presence in the diet, due to their rapid digestion rate.
As alligators get larger, it becomes less energetically efficient to consistently prey
on invertebrates. Adult alligators in this study did consume invertebrates; however, the
amount and occurrence of fresh invertebrates were minimal. This trend of reducing
invertebrate consumption with increasing size of the alligator was also evident in other
alligator diet studies (Valentine et al. 1972, Delany and Abercrombie 1986, Barr 1997,
Delany et al. 1999). It may seem that adult alligators consume large amounts of
invertebrates, however, when alligator gastric digestive rate was taken into account,
invertebrates become only a minimal part of the diet. Alligators are unable to digest
chitin (Garnett 1985), which occurs in insect exoskeleton and snail opercula and prey
items containing chitin can be over-represented in a diet study unless they are categorized
as fresh or old. When only fresh invertebrates are analyzed in detail, then over-
representation will be avoided. Since invertebrate parts containing chitin are indigestible
they either accumulate in alligator stomachs, are digested in alligator intestines, or the
alligators regurgitate the chitinous parts (Garnett 1985, Barr 1994). Barr (1994) reported
that opercula can remain in alligator stomachs for up to 200 days and observed many
captive alligators regurgitating the opercula. Fresh invertebrates generally do not
constitute much in biomass showing the true amount of invertebrates in adult alligator
Apple snails are an important prey item for juvenile alligators inhabiting Florida
and they remain part of the diet of adult alligators in Florida (Fogarty and Albury 1967,
Delany and Abercrombie 1986, Delany et al. 1988, Barr 1994, Barr 1997, Delany et al.
1999). However, apple snails can be greatly over-represented unless they are categorized
as fresh or old. In this study, apple snails were the only invertebrate that contributed
much in biomass, especially with alligators from Lakes Griffin and Woodruff. The
occurrence of snails (Pomacea spp. ) was also common in the diets of some caiman in
South America (Diefenbach 1979, Thorbjarnarson 1993, Santos et al. 1996) and were
unimportant in the diet of hatchling morelet' s crocodile (Crocodyhts moreletii) (Platt et
Louisiana alligators consumed insects and crustaceans, instead of apple snails
(Chabreck 1972, Valentine et al. 1972, McNease and Joanen 1977, Wolfe et al. 1987,
Platt et al. 1990). Blue crabs (Callinectes sapidus) were a common invertebrate
identified in alligator diets from Louisiana (Chabreck 1972, Valentine et al. 1972,
McNease and Joanen 1977, Wolfe et al. 1987, Platt et al. 1990). Apple snails do not
occur in Louisiana and therefore are not a part of alligator diets there.
Non-prey items are commonly found in the stomach of crocodilians (Fogarty and
Albury 1967, Valentine et al. 1972, McNease and Joanen 1977, Diefenbach 1979, Webb
et al. 1982, Delany and Abercrombie 1986, Taylor 1986, Magnusson et al. 1987, Wolfe et
al. 1987, Delany et al. 1988, Platt et al. 1991, Webb et al. 1991, Thorbjarnarson 1993,
Barr 1994, Tucker et al. 1996, Barr 1997, Delany et al. 1999, Silveira and Magnusson
1999, Platt et al. 2002, Pauwels et al. 2003). Non-prey items commonly found in
crocodilian stomachs were plant material, wood, rocks, and artificial objects. These
items provide no nutritional value to the crocodilians (Coulson and Hernandez 1983) and
are probably ingested incidental to prey capture.
The alligators in the study had a high occurrence of plant material, wood and
nematodes among the lakes. Most of the plant material was aquatic vegetation, seeds and
nuts. Captive American alligators have been observed eating vegetation including
elderberry (Samnbucus canadensis), citrus fruits, and leafy greens (Brueggen 2002).
These captive alligators received a nutritionally balanced captive diet and therefore the
cause of the plant ingestion was unknown (Brueggen 2002).
Some crocodilian diet studies have reported the occurrence of parasitic worms in
crocodilian stomachs (Valentine et al. 1972, Webb et al. 1982, Delany and Abercrombie
1986, Delany et al. 1988, Webb et al. 1991, Thorbjarnarson 1993). However, there are
few investigations on parasitic worms inhabiting the stomachs of American alligators
(Hazen et al. 1978, Cherry and Ager 1982, Scott et al. 1997). In this study nematodes
occurred in most of the alligator stomachs and two of the three nematodes identified
inhabiting the alligators stomach were also identified in other alligator diet studies and
parasitic investigations (Hazen et al. 1978, Cherry and Ager 1982, Delany and
Abercrombie 1986, Delany et al. 1988, Scott et al. 1997). The nematode, Ortleppa~scaris
antipini was found in both Lakes Griffin and Woodruff alligator stomachs and this
species of nematode was not previously reported in alligator stomachs.
Alligator Condition among Lakes
Body condition analyses investigate an animal's energy store compared to its
body size and are affected by abiotic and biotic components in its ecosystem (Cone 1989,
Green 2001). Condition analyses are often used to compare a population of animals over
time, compare the condition of animals across populations, or compare the condition of
animals among habitats within the same population. Comparing condition across
populations and among habitats has rarely been done with crocodilians but it can give
insight into how condition differs among habitats (Taylor 1979, Santos et al. 1994,
Delany et al. 1999).
Condition of alligators in this study was different among the lakes. Lake Apopka
alligators had the highest condition, followed by Lake Griffin alligators and Lake
Woodruff alligators had the lowest condition. Other research showed differences in
condition among habitats. Santos et al. (1994) compared condition of Caiman yacare
among different habitats within the Pantanal in Brazil. He found that caiman condition
was significantly different among habitats and found that caimans from "Miranda" river
had the highest condition. Condition differences here may be due to prey availability
among the habitats (Santos et al. 1994). Taylor (1979) compared juvenile and sub-adult
saltwater crocodile (Crocodylus porosus) condition among habitats and found great
variation. Saltwater crocodiles from upper mangroves had the highest condition and
saltwater crocodiles from freshwater swamps had the lowest condition. Saltwater
crocodiles from both habitats ate insects frequently and therefore a dietary cause to the
condition difference may not fit here (Taylor 1979).
American alligator condition comparisons also showed differences among
habitats. Zweig (2003) compared the condition of alligators among habitats using the
Fulton's K factor and found great variation. She compared alligator condition from Lake
Griffin, FL, Lochloosa Lake, FL, Orange Lake, FL, Santee, SC, Lake Woodruff, FL,
Everglades, FL, and Newnans Lake, FL, and showed a high variation in alligator
condition. Lake Griffin alligators had the highest condition and the Everglades alligators
had the lowest condition (Zweig 2003). This type of comparison encompasses a huge
geographic range of alligator habitat and offers an insight into the diverse alligator
condition among habitats. Zweig (2003) also noted that Everglades alligators have had a
consistently low condition over time and that this should not be cause for alarm. Delany
and Abercrombie (1986) found significant differences in alligator condition among lakes
in north central Florida, however, the diet of the alligators in these three lakes was not
Delany et al. (1999) found differences in alligator condition among lakes in
Florida and found that a high condition correlated with a fish dominated diet. In this
study, alligators from Lakes Apopka and Woodruff both had a fish dominated diet,
however, Lake Apopka alligators had the highest condition and Lake Woodruff alligators
had the lowest condition. The condition of the alligators may be due to more than just
dietary intake and other factors within a habitat probably play a role in alligator
In this study, diversity, equitability, and proportion of fish in alligator diets varied
among habitats and this may affect alligator condition. Lake Apopka alligators had the
highest condition and had the lowest diversity and equitability of fish in their diet. They
also had the largest proportion of fish in their diet and repeatedly ate shad. This large
dominance of fish in Lake Apopka alligator diets may be due to local abundance and
availability of shad in Lake Apopka and this may influence their high condition. Lake
Woodruff alligators had the lowest condition among the lakes and the highest diversity
and equitability of fish in their diet. Lake Woodruff alligators did not eat many fish
repeatedly, but ate fish more evenly. This may correspond to a more even prey
availability in Lake Woodruff. There may be no dominant fish taxa in Lake Woodruff as
there is in Lake Apopka. Lake Woodruff alligators had the second highest proportion of
fish in their diet. These alligators often ate fish but also often ate apple snails. This
shows how a macrophyte-dominated lake like Lake Woodruff may have more suitable
habitat for some prey species (e.g., apple snails). Lake Apopka alligators rarely ate
invertebrates and often had multiple specimens of fish in their stomachs. Since Lake
Apopka is algae-dominated, the habitat may not be as suitable for apple snails or other
invertebrates. Lake Griffin alligators had the lowest proportion of fish in their diet and
ate more non-fish vertebrate prey. Lake Griffin alligator condition fell between the
condition of alligators from Lakes Apopka and Woodruff. The different habitats the
alligators in this study inhabited may partially affect their condition due to either an
abundance of prey in the habitat and consumed by the alligators (i.e., Lake Apopka
alligators high condition) or a more evenness of prey consumption by the alligators (i.e.,
Lake Woodruff alligators low condition).
Alligator condition may also be affected by alligator density differences among
the habitats. I used night-light survey data to estimate the population of alligators > 182
cm TL on the three lakes (A. R. Woodward unpublished data, Woodward et al. 1996)
(Table 3-18). The density of Lake Apopka alligators was much lower than the densities
of alligators on the other two lakes, which were almost the same (Table 3-18) (although
Lake Apopka is a large lake with great amount of open water that is largely uninhabited
by alligators). Evert (1999) also found that the density of Lake Apopka alligators was
lower than Lake Griffin alligator density (Lake Woodruff was not included in his
research) and he found a positive correlation of alligator density with macrophyte
coverage and an inverse correlation of alligator density with human development on
lakes. Lake Woodruff is macrophyte-dominated and has little development, therefore it
fits that there would be a high alligator population density on Lake Woodruff, however,
Lake Woodruff does not have an abundance of any one species of fish. This combination
of a high density of alligators and no abundant prey may cause more intra-specific
competition for prey among the alligators and account for their low condition. A
combination of low alligator density with high resource base (i.e., shad) may account for
the Lake Apopka alligator high condition (i.e., less or no intra-specific competition for
Condition analyses use morphometric measurements to obtain a condition score
with the assumption that heavier animals of similar lengths (i.e., high condition score) are
in better health (Sutton et al. 2000). This assumption can be misleading in crocodilian
condition analyses because alligator populations with a high condition may not
necessarily live in the best environment (Delany et al. 1999, Zweig 2003). The alligators
in this study with the highest condition inhabited Lake Apopka, which is a highly
polluted lake that has experienced a fluctuating, but overall low reproductive rate for the
last two decades (Woodward et al. 1993, Rice 1996, Woodward et al. 1999). The
alligators with the lowest condition inhabited Lake Woodruff, which is the most pristine
lake out of the three in this study and alligators there have experienced a consistently
high reproductive rate (Woodward et al. 1999). Alligators may take advantage of
abundant resources in a hypereutrophic ecosystem, i.e., Lake Apopka alligators large
consumption of shad in this study, and this may increase their fat reserves and account for
their overall high condition. Lake Apopka alligators may not be the healthiest alligators
among the lakes and there may be a point where a high condition actually indicates an
excess of fat store. Therefore, caution should be used when equating health to high
condition in alligator populations.
Crocodilian condition often differs among habitats and across populations and this
may be due to resource availability. Factors affecting crocodilian diets may also affect
their condition. For example, alligators may take advantage of locally abundant prey
items in their habitat and therefore have a high condition. In a lake with more evenly
distributed prey, alligators would not have this disproportionately high resource base and
they may be smaller alligators. Alligator condition may change over time if the lake goes
through an eutrophication process. For example, if a pristine macrophyte-dominated lake
changes to an algae-dominated polluted lake supporting an abundance of prey then the
alligators may be able to take advantage of the excess prey available. In this case, the
alligator condition may increase. On the other hand, if a lake goes through a restoration
effort where certain prey are eliminated from the lake, then over time alligator condition
may decline due to the absence of the once abundant resource. Differences in condition
may also be due to a fresh or saline environment inhabited and may not be closely
associated with their diet. Other factors may contribute to alligator condition, such as
alligator hunting behavior, year round optimal temperature that prolongs feeding, distinct
wet and dry seasons affecting prey, or resource limitations. Regardless, estimating
crocodilian condition is an easy mechanism that can give insight into their health in their
habitat and it is often good to compare with a diet study, compare over time, and compare
Table 3-1. Summary of methods used to estimate fresh mass for each prey group.
Summary of Fresh Mass Estimation Methods
Prey Group Type of Biomass Estimation
Fish Allometric scaling, Hoyer and Canfield 1994
Reptiles Field Data
Amphibians Field Data
Birds Field Data, Dunning 1993
Mammals Field Data, museum specimens,
Burt and Grossenheider 1980
Gastropods Allometric scaling
Bivalves Field Data
Insects Direct Mass
Crustaceans Direct Mass
Table 3-2. Summary of samples among the lakes, including samples dropped, samples
containing fresh prey, samples containing no food items, and showing the
percentage of the samples containing fresh prey.
Total # Samples Total Total Fresh Contained % Total Fresh
Lake Samples Dropped Diet Samples Diet Samples No Food Diet Samples
Griffin 102 17 85 63 2 74
Apopka 49 5 44 33 0 75
Woodruff 49 3 46 35 1 76
200 25 175 131 3
Table 3-3. Summary of method used to collect the stomach samples.
Total Hose-Heimlich Necropsy
Lake Diet Samples Method Method
Griffin 85 69 16
Apopka 44 40 4
Woodruff 46 28 18
175 137 38
Table 3-4. Estimated total biomass of stomach content samples for alligators among the
lakes, including both vertebrate and invertebrate biomass and percentage of
Total Vertebrate Invertebrate
Lake Biomass g Biomass g % of Diet Biomass g % of Diet
Griffin 37447.5 36061.9 96 1385.6 4
Apopka 17705.1 17592.9 99 112.2 1
Woodruff 16088.9 15308 95 780.9 5
Fish Total 78 58 55 44 20309.5 54
Shad Dorosoma spp. 4 2.4 2 2.4 1322 3.5
Gizzard Shad Dorosoma cepechanum 9 4.7 8 3.5 3296 8.8
Centrarchidae 3 2.4 3 2.4 103.1 0.3
Sunfish Lepomis spp. 1 1.2 1 1.2 80 0.2
Black capePomoxis nigoauts 2 2.4 2 2.4 785 2.1
Gar Lepisosteus spp. 7 8.2 6 7.1 4489 12
CatfishAmeiurus spp 18 18.8 11 10.6 3890 10.4
Brown Bullhead Ameiurus nebulosus 11 11.8 11 11.8 4586 12.2
Yellow Bullhead Ameiurus natalis 2 1.2 2 1.2 577 1.5
Mosuto fish Gambusia holbrooki 2 2.4 2 2.4 0.2 0.001
Tilapia Oreochromis spp. 1 1.2 1 1.2 700 1.9
BowfinAmia calva 1 1.2 1 1.2 411 1.1
Sailfin Molly Poecilia latipin 1 1.2 1 1.2 0.4 0.001
Killifish Fundulus spp. 2 1.2 2 1.2 8.6 0.02
Lake Eustis pupfish Cyprinodon
variegatus hubbsi 1 1.2 1 1.2 1.2 0.003
Fish spces undetermined 12 14.1 1 1.2 60 0.2
Needlefish Strongylura marina 1 1.2 0 0 0 0
Birds Total 10 12 4 5 5763 15
Birds undetermined 4 4.7 0 0 0 0
AnhingAnhing aanhing 2 2.4 1 1.2 1235 3.3
Double crested cormorant Phalacrocorax
auritus 2 2.4 2 2.4 3628 9.7
White Ibis Eudocimus albus 1 1.2 1 1.2 900 2.4
Common Moorhen/American coot 1 1.2 0 0 0 0
Gallinula chlorou/Fulica americana
Table 3-5. Lake Griffin alligator diet data including minimum number of individuals (mni), percent occurrence, estimated mass in
grams, and percentage of the diet for prey groups and for taxa within prey groups.
RetlsTotal 45 42 15 14 3755 10
Turtle undetermined 4 4.7 0 0 0 0
Kinosternidae 6 7.1 1 1.2 105 0.3
Stinkpt turtle Sternotherus od'oratus 12 12.9 6 7.1 385 1.0
Loggerhead musk turtle Sternotherus minor 2 1.2 2 1.2 150 0.4
Redbell turtle Pseudemys nelsoni 5 5.9 1 1.2 1148 3.1
Turtle Pseud'emys spp. 3 3.5 1 1.2 13 0.03
Gope tortoise Gopherus polypemus 2 2.4 1 1.2 582 1.6
Florida softshell turtle A aone erx 1 1.2 1 1.2 386 1.0
Alligator Alligator mississippiensis 6 5.9 0 0 0 0
Co~o lllonmenth .:.- go rodon picivorus 3 3.5 1 1.2 686 1.8
Brown water snake Nerodia taxispilota 1 1.2 1 1.2 300 0.8
Mammals Total 8 11 2 2 4860 13
Mammals undetermined 6 8.2 0 0 0 0
Hisi cotton rat Sigmodon hispdu 1 1.2 1 1.2 155 0.4
Raccoon Procyon lotor 1 1.2 1 1.2 4705 12.6
Amphibians Total 6 7 5 6 1374.4 4
Amphibian undetermined 1 1.2 0 0 0 0
Greater Siren Siren lacertina 1 1.2 1 1.2 387 1
Two-toed Amphiuma Amphiuma means 1 1.2 1 1.2 287 0.8
Frog Rana sp 3 3.5 3 3.5 700.4 1.9
Table 3-5. Continued
# Fresh mni
Gastropods Total 941 74 64 28 1321.9 4
Apple snails Pomacea paltidosa 941 72.9 64 28 1321.9 4
Bivalves Total 5 4 3 4 45.0 0.1
Mussel Utterbachia spp. 5 4 3 4 45.0 0.1
Crustaceans Total 162 19 101 9 16.1 0.04
Crafs Procambarris spp 3 3.5 1 1.2 2.3 0.006
Grass shrimp Palaemonetes
intermedius 159 15.3 100 8.2 13.8 0.037
Insects Total 37 31 8 8 2.6 0.01
Eastern lubber grasshoppers Romalea
grittata 9 8.2 0 0 0 0
Drgnfly Aeschnidae 5 5.9 0 0 0 0
Water scorpion Ranatra spp. 2 2.4 2 2.4 0.2 0.001
Water bgBelostoma sp.3 3.5 2 2.4 0.2 0.001
Giant water bgLethocertis sp.1 1.2 1 1.2 0.8 0.002
Green june beetle Cotinus nitida 1 1.2 1 1.2 1 0.003
Grshpe Orthoptr 9 5.9 2 2.4 0.4 0.001
Pioneer bug Dermaptera 1 1.2 0 0 0 0
Insect undetermined 6 7.1 0 0 0 0
Table 3-5. Continued
# Total %Total Fresh Estimated % of
|mni |Occurrence |# Fresh mni |% Occurrence |Mass g |diet
Fish Total 104 84 78 64 15869 90
Shad Dorosoina spp. 46 38.6 42 36.4 3854 21.8
Gizzard shad Dorosoina cepedianuin 21 29.5 10 13.6 3210 18.1
Gar Lepisosteus spp 3 6.8 2 4.5 2826 16
Catfish 4meiurus spp. 14 25.0 7 13.6 1387 7.8
Brown bullhead 4meiurus nebulosus 2 4.5 2 4.5 701 4
Tilapia Oreochroinis spp. 8 13.6 8 13.6 3378 19.1
Centrarchidae/Cichlidae 2 4.5 1 2.3 200 1.1
Black Crape Poinoxis ni riauatus 1 2.3 1 2.3 253 1.4
Bluegill Lepoinis inacrochirus 4 2.3 4 2.3 26 0.1
Golden shiner Noteminionus crvsoleucas 1 2.3 1 2.3 34 0.2
Fish species undetermined 2 4.5 0 0 0 0
Birds Total 3 7.0 1 2.0 1235 7
Birds undetermined 2 4.5 0 0 0 0
Anhinga 4nhinga anhinga 1 2.3 1 2.3 1235 7
RetlsTotal 20 36 3 7 158 1
Kinosternidae 2 4.5 0 0 0 0
Stnpt turtle Sternotherus odoratus 5 11.4 1 2.3 35 0.2
Florida Mud Turtle Kinosternun
subrubruin 1 2.3 0 0 0 0
Gopher tortoise Gopherus polypheinus 1 2.3 1 2.3 113 0.6
Florida softshell turtle alone erx 1 2.3 0 0 0 0
Turtle undetermined 4 9.1 0 0 0 0
Alligaor alligator inississi pensis 4 11.4 0 0 0 0
Mud Snake Farancia abacura 1 2.3 1 2.3 10 0.1
Co~o lllonmenth~i, 6;Zrodon piscivorus 1 2.3 0 0 0 0
Table 3-6. Lake Apopka alligator diet data including minimum number of individuals (mni), percent occurrence, estimated mass in
grams, and percentage of the diet for prey groups and for taxa within prey groups.
Mammals Total 5 11 2 5 331 2
Mammals undetermined 3 6.8 0 0 0 0
Eastern wood rat Neotoma foridana 1 2.3 1 2.3 291 1.6
Cotton mouse Peromyscus gospnus 1 2.3 1 2.3 40 0.2
Gastropd Total 134 45 10 9 69 0.4
Apple Snails Pomacea paludosa 107 36.4 3 4.5 68 0.4
Banded mser snail Viviau georgianus 10 4.5 1 2.3 0.2 0.001
Mesa-rams-hom Planorbella scalaris 17 4.5 6 2.3 1 0.003
Crustaceans Total 23 20 9 11 15 0.1
Crayfish Procambarus spp. 5 11.4 2 4.5 13 0.1
Grass shipPalaemonetes intermedius 18 11.4 7 6.8 2 0.01
Insects Total 55 61 8 9 28 0.2
Water bu Belostoma spp 1 2.3 1 2.3 0.2 0.001
Eastern lubber grasshopper Romalea guttata 6 6.8 3 2.3 21 0.1
Grasshoppr Orhpera 21 25 2 2.3 5 0.03
Drgnfly -Aeschnidae 3 4.5 1 2.3 1.3 0.01
Insect undetermined 12 20.5 1 2.3 0.5 0.003
Beetle Elatheridae 2 2.3 0 0 0 0
Green June Beetle Cotinus nitida 10 20.5 0 0 0 0
Table 3-6. Continued
% Total # Fresh Estimated
Occurrence |Fresh mni |% Occurrence |Mass g
Fish Total 42 65 33 57 13,586 84
Gizzard shad Dorosoma cedianum 4 4.3 4 4.3 1830 11
CatfishAmeiurus spp 5 10.9 3 6.5 1600 10
Gar Leisosteus sp.2 4.3 1 2.2 424 3
Centrarchidae 7 15.2 6 13.0 503 3
Sunfish Leois sp 5 10.9 5 10.9 351 2
Warmouth Leois gulosus 1 2.2 1 2.2 144 1
Redear sunfish Lepmis microlohu 3 6.5 3 6.5 257 2
Spotted sunfish Lpmis puntatus 1 2.2 1 2.2 136 1
Largemouth bass Micropterus salmoides 4 4.3 4 4.3 6066 38
Black Crpi Pomoxis nigomclatus 1 2.2 1 2.2 80 0.5
Needdlefish Strongylura marina 3 6.5 2 4.3 182 1
Bowfin Amia calva 1 2.2 1 2.2 1763 11
Catfish Pr, .-. ..ph. itiy I spp. 1 2.2 1 2.2 250 2
Fish species undetermined 4 8.7 0 0.0 0 0
Birds Total 2 4.3 0 0 0 0
Birds undetermined 2 4.3 0 0 0 0
RetlsTotal 10 15 1 2 108 0.6
StinkpotSternotherus od'oratus 2 4.3 1 2.2 108 0.6
Loggerhead musk turtle Sternotherus
minor 1 2.2 0 0.0 0 0
Kinosternidae 1 2.2 0 0.0 0 0
Alligator Alligator mississippiensis 5 4.3 0 0.0 0 0
Snake undetermined 1 4.3 0 0.0 0 0
Table 3-7. Lake Woodruff alligator diet data including minimum number of individuals (mni), percent occurrence, estimated mass in
grams, and percentage of the diet for prey groups and for taxa within prey groups.
Mammals Total 6 13.0 1 2 289 1.8
Mammals undetermined 5 10.9 0 0 0 0
Round-tailed muskrat Keofiber alleni 1 2.2 1 2.2 289 1.8
Amphibians Total 2 4.3 2 4.3 1325 8.2
Greater siren Siren lacertina 2 4.3 2 4.3 1325 8.2
Gastropd Total 305 89.1 32 41 695.4 4.4
Apple Snails Pontacea paudosa 303 89.1 30 34.8 694.1 4.3
Banded mysterysnail Viviparus georgianus 2 2.2 2 2.2 1.3 0.01
Bivalves Total 8 13 3 4 45 0.3
Mussel Utterbachia spp. 8 13 3 4 45 0.3
Crustaceans Total 15 22 11 15 38.5 0.2
Grass shrm Palaenionetes intermedius 8 6.5 7 4.3 1.3 0.01
Crayfish Procambarus spp 2 4.3 0 0 0 0
Crayfish P. paeninsularus 1 2.2 1 2.2 19.2 0.1
Crayfish P. falax 4 6.5 3 6.5 18 0.1
Insects Total 14 28.0 5 13 2 0.01
Insect undetermined 4 8.7 1 2.2 0.1 0.001
Water bug Belostonia spp. 5 8.7 3 8.7 1.4 0.009
Drgnfl Aeschnidae 2 4.3 1 2.2 0.5 0.003
Giant water bug Lethocerus spp. 1 2.2 0 0 0 0
Beetle Stratgus spp 2 2.2 0 0 0 0
Bessbu Passalidae 2 4.3 0 0 0 0
Table 3-7. Continued
% Total # Fresh Estimated % of
Occurrence |Fresh mni |% Occurrence |Mass g |diet
Table 3-8. Shannon-Weiner diversity index (H') and Sheldon's equitability index (E)
results for alligator samples containing fresh prey. MNT represents the
minimum number of taxa consumed by the alligators for each lake.
Lake MNT H1' E
Griffin 37 2.17 0.6
Apopka 23 2.17 0.69
Woodruff 23 2.56 0.82
Table 3-9. Summary of abnormal Lake Griffin stomach content samples. These samples
were not used in the diet and condition analyses, and were abnormal based on
Schoeb et al. (2002).
Total Total Fresh Contained % Total Fresh
Samples Diet Samples No Food Diet Samples
Griffin 13 5 8 38
Table 3-10. Lake Griffin alligator shad consumption summary for this study. All fresh
shad were consumed by the alligators in 2001.
Number of Number of % % of Diet
Stomach Samples Shad Occurrence in Biomass
2001 24 10 16 12
2002 42 0 0 0
2003 19 la 5 0
aThis shad was considered old, therefore no biomass estimation was made
Table 3-11. Shannon-Weiner diversity index (H') and Sheldon's equitability index (E)
results for alligator samples containing fresh fish. MNT represents the
minimum number of taxa of fish consumed by the alligators for each lake.
Lake MNT H1' E
Griffin 13 2.13 0.83
Apopka 7 1.15 0.59
Woodruff 11 2.19 0.91
Table 3-12. Chi-square test of the occurrence of fish compared to the occurrence of other
prey (reptiles, mammals, birds, and amphibians) among the lakes. P-value
indicates significant difference. Significant differences observed than
expected in this study have a cell chi-square value greater than 1.
Frequency 37 22
Expected 44 15
Frequency 28 6
Lake Apopka Expected 25 9
Cell Chi-Square 0.32 0.92
Frequency 26 4
Expected 22 8
Total Chi-Square 7.64
Table 3-13. Frequency of occurrence for non-prey items among the lakes.
Lake Griffin Lake Apopka Lake Woodruff
% occurrence % occurrence % occurrence
Plant Material 86 86 95
Wood 79 84 83
Rocks 22 41 7
Sand 26 43 0
Nematodes 85 98 96
Artificial Objects 17 11 24
Table 3-14. Condition analysis sample summary.
Total Samples Condition
Lake Samples Dropped Samples
Griffin 102 37 65
Apopka 49 4 45
Woodruff 49 3 46
200 44 156
Table 3-15. Alligator SVL and mass summaries from each study area.
Lake Griffin Lake Apopka Lake Woodruff
SVL cm Mass kg SVL cm Mass kg SVL cm Mass kg
Mean 114 45 116 49 111 37
Minimum 78 14 88 22 88 16
Maximum 151 96 156 108 166 112
Standard Dev. 17 20 16 21 20 24
Table 3-16. LSD post hoc test results comparing the mean condition among the lakes. P-
value contrast and mean differences.
P-value contrast Mean Difference
Lake Griffin Apopka Woodruff Griffin Apopka Woodruff
Griffin <0.001* 0.009* -0.3341 0.1781
Apopka <0.001* 0.5122
* significant difference
Table 3-17. Condition score range for all alligators divided into quartiles with assigned
o average condition
ge to high condition
Quartile Score Range Rank
1st 1.69 2.46 low cc
2nd 2.47 2.67 low te
3rd 2.68 -2.93 averal
4th 2.94 4.13 high c
m Lake Griffin mean condition 2.66
m Lake Woodruff mean condition 2.48
* Lake Apopka mean condition 2.99
Table 3-18. Estimated alligator densities among the lakes.
Estimated Alligator Total Surface Alligators
Lake Population > 182 cm TL' Area (ha) per hectare
Griffin 1300 5742 0.23
Apopka 1280 12960 0.09
Woodruff 1600 6553 0.24
'based on night light surveys and Woodward et al. 1996
N= 63 33 35
Griffin Apopka Woodruff
Figure 3-1. Mean biomass (+SE) consumed by the alligators among lakes.
Frequency of Occurrence all Samples
Fiur 32.Frqeny f ccrrne f re gopsfo al re n llsapls o LkeGrffn(n85, ak Aoka(n44, n
Lake Wodrf (n=6)
Frequency of Occurrence Fresh Prey Only
Figure 3-3. Frequency of occurrence of prey groups for samples containing fresh prey only for Lake Griffin (n=63), Lake Apopka
(n=3 3), and Lake Woodruff (n=3 5).
Lake Griffin Alligator Diet
O Mammal 13%
O Bird 15%
54% H Bivalvia 0.1%
13% O Crustacea 0.04%
Figure 3-4. Percent composition by live mass for Lake Griffin alligators (N = 85).
Lake Apopka Alligator Diets
H Fish 90%
H Reptile 0.9%
OM ammal 2%
O Bird 7%
H Amphibian 0.0%
H Gastropod 0.4%
H Bivalvia 0.0%
O Crustacea 0.1%
H Insecta 0.2%
Figure 3-5. Percent composition by live mass for Lake Apopka alligators (N = 44).
Lake Woodruff Alligator Diet
0.0%, 1/ 0.01%"
2%, 'L Fish 84%
O Mammal 2%
O Bird 0.0%
H Amphibian 8%
H Gastropoda 4%
H Bivalvia 0.3%
O Crustacea 0.2%
H Insecta 0.01% vi
Figure 3-6. Percent composition by live mass for Lake Woodruff alligators (N = 46).
F4 40 I
N= 63 33 35
Griffin Apoka Woodruff
Figure 3-7. Mean fish composition (+SE) for alligators among the lakes.
Size Range of Alligators (TL) by Lake
Figure 3-8. Size (TL) of alligators sampled in this study divided into quartiles and compared among the lakes.
Size Range of Alligators (TL) Observed during NL Surveys
Figure 3-9. Estimated sizes (TL) of alligators observed during night light surveys from each study area (A. R. Woodward, Florida
Fish and Wildlife Conservation Commission unpublished data).
N= 65 45 46
Griffin Apopka Woodruff
Figure 3-10. Mean condition (+ SE) of alligators among lakes.
S ample s
Figure 3-11. Cumulative species recorded with increased sample size.
The hose-Heimlich technique was an effective and efficient way of obtaining the
stomach contents from live adult alligators 5 290 cm TL. Analysis of the stomach
contents was successfully completed by examining frequency of occurrence of all prey,
frequency of occurrence of fresh prey, and with percent composition by live mass for
fresh prey. These quantitative analyses complemented each other and provided the best
means to examine the diet of the alligators among the lakes.
Alligator diets varied among the lakes. Fish was the number one prey group for
all alligators among the lakes, but there were large differences in species composition
consumed and number of fish consumed among the lakes. Lake Griffin alligators had the
lowest percentage of fish in their diet and ate more non-fish prey groups. Lake Apopka
alligators had the lowest diversity and equitability of fish in their diet and repeatedly ate
shad. Lake Woodruff alligators had the highest diversity and equitability of fish in their
diet and ate more sunfish and bass.
Habitat and prey availability may play a role in alligator diets. Lakes with
different trophic states may have different prey available. Lakes occupying different
geographic locations may offer different prey. In addition, as lakes change either through
eutrophication or through restoration, the prey available to the alligators will also change.
Therefore, managers need to be aware that changes in lakes due to either trophic state
changes or restoration will affect the fish community. Because alligators are very
opportunistic predators that occupy a variety of habitats, they will take advantage of
locally available and abundant prey items.
The recent adult alligator mortality on Lake Griffin may or may not have been
associated with their diet. The diet of the alligators may give clues to their health and a
diet of shad with high level of thiaminase may cause a thiamin deficiency in alligators,
but there are probably other factors in Lake Griffin that are contributing to their
mortality. This seems especially plausible because Lake Apopka alligators consumed a
great abundance of shad, which had high levels of thiaminase and that lake was not
experiencing a great amount of adult alligator mortality. More research needs to be done
to truly understand the cause of the Lake Griffin alligator mortality.
The Fulton's condition factor provided a quick assessment of alligator condition
and allowed for a comparison across populations. Alligator condition varied among
habitats and this may or may not be due to alligator diets. Lake Apopka alligators had the
highest condition and the highest proportion of Esh in their diet. Lake Griffin alligators
had the median condition, ate more non-Hish prey items, and Lake Woodruff alligators
had the lowest condition, ate fish more evenly with a high diversity and had the second
highest proportion of fish in their diet. Other factors such as alligator density, alligator
hunting behavior, genetics, prolonged feeding period, or wet/dry seasons could play a
role in alligator condition. In addition, caution should be used when equating a high
condition to better health. Lake Apopka alligators had the highest condition; however,
that system has been severely polluted over the last half century and the alligators there
have experienced a low reproductive rate. Lake Woodruff alligators inhabit the most
pristine environment out of the three and their condition was the lowest overall.
LIST OF REFERENCES
Allen, M.S., M.V. Hoyer, and D.E. Canfield, Jr. 2000. Factors related to gizzard shad
and threadfin shad occurrence and abundance in Florida lakes. Journal of Fish
Anderson, R.O. and R.M. Neumann. 1996. Length, weight, and associated structural
indices. Pages 447-482 in Fisheries Techniques, 2nd edition (B.R. Murphy and
D.W. Willis, eds.). American Fisheries Society, Bethesda, Maryland, 732 pp.
Bachmann, R. W., B. L. Jones, D. D. Fox, M Hoyer, L. A. Bull, and D. E. Canfield, Jr.
1996. Relations between trophic state indicators and fish in Florida (U. S.A.)
lakes. Canadian Journal of Fisheries and Aquatic Science, 53:842-855.
Bachmann, R.W., M.V. Hoyer, D.E. Canfield, Jr. 2001. Sediment removal by the Lake
Apopka marsh flow-way. Hydrobiologia, 448:7-10.
Barr, B.R. 1994. Dietary studies on the American alligator Alligator mississippiensis, in
southern Florida. Master's Thesis, University of Miami, Coral Gables. 73 pp.
Barr, B.R. 1997. Food habits of the American alligator, Alligator mississippiensis, in the
southern Everglades, Ph.D. Dissertation., University of Miami, Coral Gables, Fl.
Bowen, S.H. 1996. Quantitative Description of the Diet. Pages 325-336 in Fisheries
Techniques, 2nd edition (B.R. Murphy and D.W. Willis, eds.). American Fisheries
Society, Bethesda, Maryland, 732 pp.
Brown, J.H. and G.B. West, eds. 2000. Scaling in Biology. Oxford University Press,
New York. 352 pp.
Brueggen, J.D. 2002. Crocodilians: Fact or Fiction. Proceedings of the 16th Working
Meeting of Crocodiles Specialist Group of the Species Survival Commission of
Burt, W.H. and R.P. Grossenheider. 1980. Peterson Field Guide, Mammals, 3rd edition.
Houghton Mifflin Company, New York. 289 pp.
Canfield, D.E. Jr., R. W. Bachmann, and M.V. Hoyer. 2000. A management alternative
for Lake Apopka. Lake and Reservoir Management 16:205-221.
Casteel, R. W. 1974. A method for estimation of live weight of fish from the size of
skeletal remains. American Antiquity. 39:94-97.
Chabreck, R.H. 1972. The foods and feeding habits of alligators from fresh and saline
environments in Louisiana. Proceedings Annual Conference of Southeastern
Association of Game and Fish Commission, 25:1 17-124.
Cherry, R.H. and A.L. Ager. 1982. Parasites of American alligators (Alligator
mississipiensis) in South Florida. Journal of Parasitology, 68:509-5 10.
Cone, R.S. 1989. The need to reconsider the use of condition indexes in fishery science.
Transactions of the American Fisheries Society, 1 18:510-514.
Coulson, R.A. and T. Hemnandez. 1983. Alligator Metabolism, Studies in Chemical
Reactions in vitro. Pergamon Press, New York. 182 pp.
Delany, M.F. 1990. Late summer diet of juvenile American alligators. Journal of
Delany, M. F. and C. L. Abercrombie. 1986. American alligator food habits in north
central Florida. Journal of Wildlife Management, 50:348-353.
Delany, M.F., A.R. Woodward, and I.H. Kockel. 1988. Nuisance alligator food habits in
Florida. Florida Field Naturalist, 16:86-90.
Delany, M.F., S. B. Linda, and C.T. Moore. 1999. Diet and condition of American
alligators in 4 Florida lakes. Proceedings Annual Conference of Southeastern
Association of Fish and Wildlife Agencies, 53:375-3 89.
Diefenbach, C.O. da C. 1979. Ampullarid gastropod staple food of Caiman
latirostris? Copeia. 1:162-163.
Dunning, J.B.,Jr. 1993. CRC Handbook of avian body masses. CRC Press, Inc, Boca
Raton, Fl., 371 pp.
Evert, J.D. 1999. Relationships of alligators (Alligator mississippiensis) population
density to environmental factors in Florida lakes. Master's Thesis. University of
Florida, Gainesville, Fl., 122pp.
Fernald, E.A. and E.D. Purdum. 1998. Water Resources Atlas of Florida. Institute of
Science and Public Affairs, Florida State University, Tallahassee, Fl. 309 pp.
Fitzgerald, L.A. 1989. An evaluation of stomach flushing techniques for crocodilians.
Journal of Herpetology, 23 :170-172.
Fogarty, M.J., and J. D. Albury. 1968. Late summer food of young alligators in Florida.
Proceedings Annual Conference of Southeastern Association of Game and Fish
Garnett, S.T. 1985. The consequences of slow chitin digestion on crocodile diet analysis.
Journal of Herpetology, 19:303-304.
Green, A.J. 2001. Mass/length residuals: measures of body condition or generators of
spurious results? Ecology, 82:1473-1483.
Hazen, T.C., J.M. Aho, T.M. Murphy, G.W. Esch, and G.D. Schmidt. 1978. The
parasite fauna of the American alligator (Alligator mississippiensis) in South
Caronlina. Journal of Wildlife Diseases, 14:435-439.
Heimlich, H.J. 1975. A life-saving maneuver to prevent food-choking. Journal of
American Medical Association, 234:398-401.
Hoyer, M.V. and D.E. Canfield, Jr. 1984. Handbook of common freshwater fish in
Florida lakes. University of Florida Press, Gainesville, Fl. 178 pp.
Janes, D. and W.H.N. Gutzke. 2002. Factors affecting retention time of turtle scutes in
stomachs of American alligators, Alligator mississippiensis. American Midland
Krebs, C.J. 1999. Ecological Methodology. Harper Collins Publisher, Menlo Park, Ca.
Kushlan, J.A., and J.C. Simon. 1981. Egg manipulation by the American alligator.
Journal of Herpetology, 15:45 1-454.
Lowe, E.F., L.E. Battoe, M.F. Coveney, C.L. Schelske, K.E. Havens, E.R. Marzolf, and
K.R. Reddy. 2001. The restoration of Lake Apopka in relation to alternative
stable states: an alternative view to that of Bachmann et al. (1999).
Ludwig, J.A. and J.F. Reynolds. 1988. Statistical Ecology a primer on methods and
computing. John Wiley and Sons, New York. 337 pp.
Magnusson, W. E., E.V. da Silva, and A.P. Lima. 1987. Diets of Amazonian
crocodilians. Journal of Herpetology, 21:85-95.
McNease, L. and T. Joanen. 1977. Alligator diets in relation to marsh salinity.
Proceedings Annual Conference of Southeastern Association of Fish and Wildlife
Murphy, B.R., M.L. Brown and T.A. Springer. 1990. Evaluation of the relative weight
(Wr) index, with new applications to walleye. North American Journal of
Fisheries Management, 10:85-97.
Pauwels, O.S.G., V. Mamonekene, P. Dumont, W.R. Branch, M.Burger, and S.Lavoue.
2003. Diet records for Crocodyhts cataphractus (Reptilia: Crocodylidae) at Lake
Divangui, Ogooue-Maritime Province, Southwestern Gabon. Hamadryad,
Peterman, R.M. 1990. Statistical power analysis can improve fisheries research and
management. Canadian Journal of Fisheries and Aquatic Science, 47:2-15.
Platt, S.G., C.G. Brantley, and R.W. Hastings. 1990. Food Habits of Juvenile American
Alligators in the Upper Lake Pontchartrain Estuary. Notheast Gulf Science,
Platt, S.G, T.R. Rainwater, and S.T. McMurry. 2002. Diet, gastrolith acquisition and
initiation of feeding among hatchling Morelet' s crocodiles in Belize.
Herpetological Journal, 12:81-84.
Reitz, E.J., I.R. Quitmyer, H.S. Hale, S. J. Scudder, and E.S. Wing. 1987. Application of
allometry to zooarchaeology. American Antiquity, 52:304-317.
Rice, K.G. 1996. Dynamics of exploitation on the American alligator: environmental
contaminants and harvest. Ph.D. Dissertation. University of Florida, Gainesville,
Ross, J.P. editor 1998. Status survey and conservation action plan, Crocodiles.
IUCN/SSC Crocodile Specialist Group, Gainesville, FL, 96 pp.
Santos, S.A., M.J.S. Nogueira, M.S. Pinheiro, G.M. Mourao and Z. Campos. 1994.
Condition factor of Caiman crocodihts yacare in different habitats of Pantanal
Mato-Grossense. Proceedings of the 12th Working Meeting of Crocodiles
Specialist Group of the Species Survival Commission of the IUCN.
Santos, S.A., M.S. Nogueira, M.S. Pinheiro, Z. Campos, W.E. Magnusson, and G. M.
Mourao. 1996. Diets of Caiman crocodihts yacare from different habitats in the
Brazilian Pantanal. Herpetological Journal, 6: 111-117.
Schoeb, T.R., T.G. Heaton-Jones, R.M. Clemmons, D.A. Carbonneau, A.R. Woodward,
D. Shelton, and R.H. Poppenga. 2002. Clinical and necropsy findings associated
with increased mortality among American alligators of Lake Griffin, Florida.
Journal of Wildlife Diseases, 38:320-337.
Scott, T.P., S.R. Simcik, and T.M.Craig. 1997. Endohelminths of American alligators
(Alligator mississippiensis) from Southwest Texas. Journal of Helminthology,
Searcy-Bernal, R. 1994. Statistical power and aquacultural research. Aquaculture,
Silveira, R.D. and W.E. Magnusson. 1999. Diets of Spectacled and Black Caiman in the
Anavilhanas Archipelago, Central Amazonia, Brazil. Journal of Herpetology,
SPSS Inc., 2000. SPSS Base 11.0 for Windows user' s guide. SPSS Inc. Chicago, IL.
Sutton, S.G., T.P. Bult, and R.L. Haedrich. 2000. Relationships among fat weight, body
weight, water weight, and condition factors in wild Atlantic salmon parr.
American Fisheries Society, 129:527-538.
Taylor, D. 1986. Fall foods of adult alligators from Cypress Lake habitat, Louisiana.
Proceedings of Annual Conference of Southeastern Association of Fish and
Wildlife Agencies, 40:338-341.
Taylor, J.A., G.J. Webb, and W.E. Magnusson. 1978. Methods of obtaining stomach
contents from live crocodilians. Journal of Herpetology, 12:413-415.
Taylor, J.A. 1979. The foods and feeding habits of subadult Crocodylus porosus
Schneider in Northern Australia. Australian Wildlife Research, 6:347-359.
Thorbjarnarson, J.B. 1993. Diet of the spectacled caiman (Caiman crocodilus) in the
central Venezuelan Llanos. Herpetologica. 49:108-117.
Tucker, A.D., C.J. Limpus, H.I. McCallum, and K.R. McDonald. 1996. Ontogentic
dietary partitioning by Crocodylus johnstoni during the dry season. Copeia
Valentine, J. M., J. R. Walther, K. M. McCartney, and L. M. Ivy. 1972. Alligator diets
on the Sabine National Wildlife Refuge, Louisiana. Journal of Wildlife
Webb, G.J.W., S.C. Manolis, R. Buckworth. 1982. Crocodylus johnstoni in the
McKinlay River area, N.T.I. variation in the diet, and a new method of assessing
the relative importance of prey. Australian Journal of Zoology. 30:877-899.
Webb, G.J.W., G.J. Hollis, and S.C. Manolis. 1991. Feeding, growth, and food
conversion rates of wild saltwater crocodiles (Crocodylus porosus). Journal of
Wolfe, J.L., D.K. Bradshaw, and R.H. Chabreck. 1987. Alligator feeding habits: new
data and a review. Northeast Gulf Science, 9:1-8.
Woodward, A.R., H.F. Pervcival, M.L. Jennings, and C.T. Moore. 1993. Low clutch
viability of American alligators on Lake Apopka. Florida Scientist, 56:42-64.
Woodward, A.R., K.G. Rice, and S.B. Linda. 1996. Estimating sighting proportions of
American alligators during night-light and aerial helicopter surveys. Proceedings
Annual Conference of Southeastern Association of Fish and Wildlife Agencies,
Woodward, A.R., D.S. Bermudez, and D.A. Carbonneau. 1999. A preliminary report on
alligator clutch viability in Florida. Unpublished manuscript. Florida Fish and
Wildlife Conservation Commission.
Zweig, C.L. 2003. Body condition index analysis for the American alligator (Alligator
mississippiensis). Master's Thesis, University of Florida, Gainesville, Fl. 49 pp.
Amanda N. Rice was born in Leesburg, Florida, on 8 October 1974 and grew up in
Mount Dora, Florida. Amanda was always fascinated with animals and the outdoors and
decided she wanted to devote her life to working with animals. She obtained her A.S.
degree in the Zoo Animal Technology program from Santa Fe Community College in
August 1995 and then went on to obtain a B.S. degree in zoo science from Friends
University in May 1997. Amanda then proceeded to work at the Jacksonville Zoological
Gardens from July of 1997 until August of 2001. While working there, her love for
animals grew even stronger as she was able to work with a variety of exotic mammal
species. Amanda primarily worked with primates and absolutely loved working with the
gorillas. After four years of devotion to the Jacksonville Zoo, she decided to fulfill her
goal of obtaining a master' s degree and began graduate work at the University of Florida.
Amanda' s devotion to captive animal care shifted and she became very interested in
working with native Florida wildlife. While in graduate school, Amanda fell into the
alligator world and became a member of the Florida Alligator Research Team. Prior to
graduation Amanda obtained a job as a biological scientist working with amphibians,
alligators, and crocodiles and plans to continue her career working with Florida's