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TECHNICAL REPORT NO. 29
EVALUATION OF ALLIGATOR HATCHLING AND EGG
REMOVAL FROM 3 FLORIDA LAKES
H. Franklin Percival
and
Michael L. Jennings
Final Report Submitted by:
Cooperative Fish and Wildlife Research Unit
Department of Wildlife and Range Sciences
School of Forest Resources and Conservation
University of Florida
Gainesville, FL 32611
Supported by:
Florida Alligator Farmers Association
Florida Game and Fresh Water
U. S. Fish and Wildife Service
Univeristy of Florida
April 1987
r'
ACKNOWLEDGEMENTS
The Florida Cooperative Fish and Wildlife Research Unit, Florida
Game and Fresh Water Fish Commission, and the Florida Alligator Farmers
Association jointly supported this research project. C. Abercrombie, A.
Woodward, and T. Hines assisted in developing the frame work for data
collection and interpretation. D. Ashley, and members of the Florida
Alligator Farmers Association provided financial support, equipment,
facilities and personnel. D. David, M. Delany, C. McKelvy, J. White, L.
Hord, G. Holder, T. Reagan, T. Stice, J. Defazio, A. Bush, J. Clugston
assisted in data collection. D. Carlberg provided flawless helicopter
service when requested. We extend our gratitude to these institutions
and people and to the many others who contributed voluntary assistance.
INTRODUCTION
The ranching of eggs and juveniles is an important aspect of
successful crocodilian management programs throughout the world. In
1972, Papua New Guinea began its commercial ranching program which
currently harvests wild Crocodylus porosus and C. novaegineae juveniles
for captive rearing (Rose 1982, National Resource Council 1983). In
Zimbabwe, C. niloticus eggs are collected from wild nests and incubated
and reared on farms. Similarly, in Louisiana, Alligator
mississippiensis eggs are collected and incubated by the Louisiana
Wildlife and Fisheries Commission and then distributed to qualified
alligator farms. Governments in Australia, Africa, Asia, Central
ACKNOWLEDGEMENTS
The Florida Cooperative Fish and Wildlife Research Unit, Florida
Game and Fresh Water Fish Commission, and the Florida Alligator Farmers
Association jointly supported this research project. C. Abercrombie, A.
Woodward, and T. Hines assisted in developing the frame work for data
collection and interpretation. D. Ashley, and members of the Florida
Alligator Farmers Association provided financial support, equipment,
facilities and personnel. D. David, M. Delany, C. McKelvy, J. White, L.
Hord, G. Holder, T. Reagan, T. Stice, J. Defazio, A. Bush, J. Clugston
assisted in data collection. D. Carlberg provided flawless helicopter
service when requested. We extend our gratitude to these institutions
and people and to the many others who contributed voluntary assistance.
INTRODUCTION
The ranching of eggs and juveniles is an important aspect of
successful crocodilian management programs throughout the world. In
1972, Papua New Guinea began its commercial ranching program which
currently harvests wild Crocodylus porosus and C. novaegineae juveniles
for captive rearing (Rose 1982, National Resource Council 1983). In
Zimbabwe, C. niloticus eggs are collected from wild nests and incubated
and reared on farms. Similarly, in Louisiana, Alligator
mississippiensis eggs are collected and incubated by the Louisiana
Wildlife and Fisheries Commission and then distributed to qualified
alligator farms. Governments in Australia, Africa, Asia, Central
America, and South America currently are investigating the feasibility
of commercial ranching of crocodiles.
Though the concept of juvenile or egg harvests is not new,
uncertainties exist regarding short and long-term impacts on harvested
populations. In Florida, where demand for alligator young and eggs is
expanding, identification of potential biological impacts associated
with future management programs is imperative. Florida's harvest
program has been based on an experimental study which evaluates the
biological impact of removal.
Our concept of alligator ranching assumes that harvest rates of
eggs and juveniles depends largely on the degree to which compensatory
mechanisms function in alligator populations. That not all production
is necessary to maintain populations indicates that density independent
and density dependent mechanisms are functioning in alligator
populations from the egg stage through the first few years of life. The
nature of the effects of these mechanisms on populations ultimately will
provide a guide for management decisions regarding future harvest
programs.
The primary objective was to evaluate the impacts on alligators
populations when 50% of the annual production was removed from 3 study
sites in central Florida. Specific research objectives of this study
were to: (1) compare clutch size, fertility, hatchability rates for each
clutch from each study area; (2) evaluate growth rates of early
age-class alligators from all treatment lakes and control area Lake
Woodruff; and (3) document changes in population size and structure on
the study areas.
STUDY AREAS
Study areas were selected based on the following criteria: (1)
they should contain relatively dense alligator populations such that any
changes in population demography could be adequately quantified; (2)
they should contain at least superficial similarities in terms of basin
type, hydrological characteristics and marsh plant communities; and (3)
adequate nesting should exist to satisfy sample size requirements for
nesting studies ( 50 nests/year). Thus, Lakes Griffin, Jessup, and
Apopka were chosen as treatments and Lake Woodruff selected as a
control. Paynes Prairie was utilized as a control only for evaluating
annual variations in nesting.
Lakes Griffin (5860 ha) and Apopka (12141 ha) are eutrophic,
hardwater natural lakes with unconsolidated substrates in the Oklawaha
chain of lakes within the central valley physiographic region of Florida
(Canfield 1981). Lake Griffin receives water primarily through rainfall
and the canals connecting it with Lake Yale and Lake Eustis. It drained
to the north through the Oklawaha River. The southern half of shoreline
is highly developed, while much of the east central marsh has been
drained and cleared for vegetable farming and improved pasture. Bottom
substrates include muck and sand, supporting very little submergent or
emmergent vegetation. Most of the 3815 ha of wooded marsh occurs in a
narrow band proximal to open water areas in the northern half of the
lake and is characterized by Carolina willow (Salix caroliniana), wax
myrtle (Myrica cerifera), red maple (Acer rubrum), blackberry (Rubus
rubripes), and elephant ear (Colocasia esculentum). A true wet marsh
(4265 ha) occurs outside this association characterized by sawgrass
(Cladium jamaicense), maidencane (Panicum hemitomon), cinnomon fern
(Osmunda cinnamomea), sedges (Carex spp.), and rushes (Juncus spp.).
Lake Apopka receives water from rainfall, runoff and springs and
draines northward through the Beauclair canal. Pumps re-circulate water
for agricultural purposes in the former northern marshes. About 96% of
Lake Apopka's northern marsh (13000 ha) was diked and drained in the
1940's for agricultural purposes. The small remnant (543 ha) of the
original marsh is dominated by Carolina willow and arrowhead (Sagittaria
lancifolia). Surrounding much of the remaining shoreline is wooded
marsh (3988 ha) comprised of swamp tupelo (Nyssa sylvatica), bald
cypress (Taxodium distichum), red maple, Carolina willow, wax myrtle,
and arrowhead.
Lakes Jessup (4452 ha) and Woodruff (2429 ha) are eutrophic,
alkaline, natural lakes, with unconsolidated substrates in the St.
John's River drainage system in east central Florida (Canfield 1981).
Much of Lake Jessup's western shore has been cleared and converted to
improved pasture. The undisturbed northeastern marsh (5843 ha) is
dominated by sand cordgrass (Spartina bakeri) and giant reed (Phragmites
australis), whereas the wooded southern marsh (1673 ha) contains bald
cypress, swamp tupelo, and red maple. Water levels are regulated by
hydrological fluctuation in the St. John's River.
Lake Woodruff and its surrounding marsh were incorporated into a
National Wildlife Refuge in 1964 and have not been developed. Logging
dikes constructed during the 1950's surround much of Lake Woodruff's
perifery and provide borrow pits and support for sweetgum (Liquidambar
styraciflua), swamp tupelo, red maple, Carolina willow and bald cypress.
The remaining wooded marsh contains naturally occurring tree islands and
wooded sloughs. Beyond the spoil berms, vast expanses (1214 ha) of sand
cordgrass dominate. Unlike the other study areas, Lake Woodruff
supports significant submergent plant growth, principally banana
waterlily (Ceratophyllum demersum) and eel grass (Vallisneria ,
americana). Water inflow and outflow from Lake Woodruff are regulated
primarily by fluctuations in the St. John's River.
Paynes Prairie is a 8599 ha shallow, emergent marsh with only 605
ha of open water (Alachua Lake). Its substrate is composed of deep
organic material which supports growths of water loosestrife (Decodon
verticillatus), water primrose(Ludwigia peruviana), maiden cane, cattail
(Typha latifolia) and pickerelweed (Pontederia lanceolata). Paynes
Prairie receives water through lateral permeability of the Florida
Aquifer, rainfall and runoff from Gainesville and is drained by a
natural sink on the northeastern shoreline. Water is regulated by a
network of dikes and control structures. The dikes support upland
plants and wood vegetation (e.g. waxmyrtle and Carolina willow). Two
major highways (U.S. 441 and 1-75) traverse the system from north to
south in its western portion.
METHODS
Removal Rate
Experimental removal rates were evaluated for their potential
impacts on alligator populations. Specifically, we were interested in
targeting the total surviving production on each study area. This
required adjustments of production estimates to account for natural
mortality due to predation. We felt that a 50% removal rate on
surviving hatchlings and nests was high enough to impact populations but
cordgrass dominate. Unlike the other study areas, Lake Woodruff
supports significant submergent plant growth, principally banana
waterlily (Ceratophyllum demersum) and eel grass (Vallisneria ,
americana). Water inflow and outflow from Lake Woodruff are regulated
primarily by fluctuations in the St. John's River.
Paynes Prairie is a 8599 ha shallow, emergent marsh with only 605
ha of open water (Alachua Lake). Its substrate is composed of deep
organic material which supports growths of water loosestrife (Decodon
verticillatus), water primrose(Ludwigia peruviana), maiden cane, cattail
(Typha latifolia) and pickerelweed (Pontederia lanceolata). Paynes
Prairie receives water through lateral permeability of the Florida
Aquifer, rainfall and runoff from Gainesville and is drained by a
natural sink on the northeastern shoreline. Water is regulated by a
network of dikes and control structures. The dikes support upland
plants and wood vegetation (e.g. waxmyrtle and Carolina willow). Two
major highways (U.S. 441 and 1-75) traverse the system from north to
south in its western portion.
METHODS
Removal Rate
Experimental removal rates were evaluated for their potential
impacts on alligator populations. Specifically, we were interested in
targeting the total surviving production on each study area. This
required adjustments of production estimates to account for natural
mortality due to predation. We felt that a 50% removal rate on
surviving hatchlings and nests was high enough to impact populations but
low enough to insure that drastic population declines would not occur.
Further, a 50% removal was considered the maximum work load that could
be efficiently implemented and managed.
Nest Production & Success
Nest surveys were conducted from 5-25 July each year to determine
total nesting effort. Helicopters were used in 1981, and 1983-1986. A
fixed wing aircraft modified for slow flight (approximately 96 kph) also
was used to search for nests in 1982. Helicopter survey altitude was
maintained at 30 to 50 m except when nest status determination required
hovering 5 to 20 m above nests. Survey routes were flown parallel with
the shoreline when marsh areas were narrow. In more extensive marsh
habitat parallel routes approximately 100 m apart were traversed. All
potential nesting habitat was surveyed.
Nest locations and their status (active, depredated, false,
flooded or unknown fate) were recorded during the initial survey on
aerial photographs. The second and third surveys were conducted to
determine nest status during late incubation (early August) and
post-hatching (late September) periods, respectively. Previously
undiscovered nests found during these two flights were documented
similarly to those on the initial survey. Unhatched nests observed
during the final survey were not utilized in analyses of nest mortality
because final fate could not accurately be estimated.
Active nests were distinguishable as intact domes approximately 1.5
m in diameter and 0.5 to 1.0 m in height (Joanen 1969, Campbell 1972).
Active nests located during post-hatching surveys were characterized as
having a semi-circular excavation from the top center down to the bottom
of the egg cavity (Deitz and Hines 1980). Depredated nests were
distinguished as being flattened with nest material scattered and
alligator eggs or shell fragments littering the immediate area. To
circumvent overestimation of depredation in years where clutches were
removed, 2 separate depredation rates were averaged. Overall
depredation rate (D ) was estimated by:
(DI/AI) + (D2/A2)
2
where: D1 = total number of aerially observed nests depredated prior to
clutch removal; Al = total nests aerially observed during first survey;
D2 = number of aerially sighted nest depredated after clutch removal
and; A2 = number nests remaining after egg removal. A2 was estimated
by:
(A1-D1)-R
where R = number of clutches removed. On Lake Woodruff and in years
where clutches were not removed from Lakes Griffin, Jessup, and Apopka,
depredation rates were calculated as the total number of nests
depredated throughout incubation divided by the total number of nests
aerially observed. Nests were considered flooded if submerged by
two-thirds or more. Positive identification of false nests varied among
wetland systems, but generally appeared smaller, often incomplete and in
most instances in close association with larger true nests. Some nests
lost identifiable visual characteristics, or were located in dense
vegetative cover which obscured visibility in later surveys. The final
status of these nests was considered to be in proportion to those nests
with known final status.
Total nesting estimates (N) were calculated by:
N = A+ H
where: A = the total number of air-sighted nests; and H = est-imate of
the number of nests not seen during aerial survey, where H was estimated
by:
H = P/D,
where: P = number of pods found during post hatch night-light survey
that were not associated with an air-sighted nest. We assumed that nest
success was independent of nest density and that the hatching success
rate for unobserved nests equalled observed nests.
Hatchling/Egg Removal
A 50% removal of production on the 3 treatment lakes was
accomplished by hatchling collection during the fall and spring of 1981
and 1982 nesting seasons, a combination of egg and hatchling collection
in 1983, and egg collection from 1984 1986.
Hatchling collections were initiated in early September after the
final aerial survey, continued through October, and resumed in March.
Night searches were conducted from airboats using Kohler wheat-lites
with 15,000 60,000 cp bulbs. Pods or sibling groups of hatchlings
were identified by the faint red reflection of the spotlight from their
eyes. After locating a pod, individuals were captured by hand or
Pilstrom tongs and placed in 5 gallon plastic buckets. When no more
hatchlings were sighted or could be heard (distress calling) the
location was inconspicuously marked with flagging tape and a plant tag
(10 mm X 70 mm) identifying the nest number. The location of the pod
was recorded on a Mark Hurd (1:2400) aerial photograph. These locations
were compared with those plotted during aerial surveys and provided
information on association of collected pods with air-sighted
nests. Some pod locations were revisited throughout the fall and spring
to collect hatchlings previously missed.
Upon completion of a search, hatchlings were tagged on the web of
the right rear foot between the 2nd and 3rd toes with a number 1 monel
tag bearing the inscription FSP (Farm Supplement Project) followed by a
4 digit number. For each pod, information on the number of hatchlings,
tag numbers, collection site characteristics, female behavior, and
environmental conditions was recorded. Hatchlings were transported to
alligator farms within 48 hours of collection.
In 1983 a portion of the targeted removal included taking eggs from
as many nests as could be located during ground searches. From
1984-1986 egg removal was the only technique used and required that nest
be visually located by helicopter. Ground crews in airboats were then
directed to nest locations via air-ground communications. Ground crews
collected information on nest size, relative humidity, estimated
percentage daily shade and status (dry, partially flooded or flooded),
female presence and behavior, nesting habitat and comments regarding
peculiarities of the nest site. After excavating the nest, clutch size,
and egg status (fertile, infertile, dry, partially flooded, flooded)
were recorded. Eggs were individually marked on their uppermost surface
with a felt-tipped waterproof marker to indicate their relative position
as they were removed from the nest. To reduce any potential toxicity of
the ink, eggs were not marked on the developmental band during 1985 and
1986. Eggs less than 25% inundated with water were considered dry and
marked with black ink; 25-75% inundated eggs were considered partially
flooded and marked red; and over 75% inundated eggs were considered
flooded and marked blue. Eggs then were positioned (set) in the
incubation trays (plastic bus pans 61 cm X 39 cm) such that relative
position in the nest cavity could be determined. The incubation pan was
filled with approximately 5 cm of natural nest material upon which eggs
were placed. The eggs were then covered with seasoned hay.
During transportation of the incubation tray extreme care was taken
to avoid excessive vibration or shock. In the majority of cases, one
individual was directed to hold the incubation tray to avoid contact
with any part of the boat while in transit (usually <1 km) to the egg
transport boat. The latter was a 16 foot Panther (the mention of
tradename does not constitute endorsement or recommendation for use by
the Federal government) aluminum airboat with the passenger seat removed
to accommodate the egg platform (five inflated tire inner tubes placed on
the floor of the airboat and sheets of 1/2" plywood and 2 inch foam
rubber separated layers of 10 egg trays). Where possible, the transport
boat was carefully maneuvered in sheltered waters to avoid excessive
vibration. Eggs were transported to incubators in a covered pickup
truck on the same cushioned platform. Temperatures were monitored to
insure that eggs were maintained between 280 and 32C during transport
to incubators.
After arrival at a farm, eggs were transilluminated to check for
fertility and egg band development (Ferguson 1981, Webb and Manolis
1987). Infertile eggs were identified by the lack of an opaque embryo
attachment spot or band and were discarded. If band development was
visibly retarded or if vascular pigmentation was not similar to that of
other apparently health eggs in the clutch, the egg in question was
opened and the status (strong, good, weak, or dead) of the embryo
recorded. One healthy egg was removed from each clutch and sacrificed
for determination of clutch age. In 1984 embryo age was estimated by
back-dating from the hatch date of each clutch. In 1985 and 1986 a
combination of back-dating, embryological development charts, and egg
banding (Ferguson 1981) were used to determine embryo age. Eggs were
transilluminated again approximately 3 to 4 weeks later to identify eggs
containing embryos that were originally missed or that had died since
the first check. Unhatched eggs from each clutch also were opened and
embryos checked for age at death.
Night-Light Counts
Night-light counts were used to evaluate population trends on all
study areas (Wood and Humphrey 1983). Most surveys were conducted
during late May and June, 1980-1986 with airboats or outboard motor
boats. One survey per year was conducted on Lakes Griffin and Apopka
from 1980-1982, and on Lakes Jessup and Woodruff from 1981-1982. Two
replicate surveys were conducted on all lakes from 1983-1986 with the
exception of only one survey on Lake Griffin during 1985. The replicate
surveys were conducted within a 1 month period to reduce variation of
environmental factors such as air and water temperature, and water
levels (Woodward and Marion 1979).
Standard survey routes (Figs. 1, 2, 3, 4) were run with a 200,000
cp light to detect alligator eye reflections. Once spotted, each animal
was approached and its size estimated in 1 ft. length categories.
Animals that submerged or were not clearly visible (dense vegetation)
were classified in general size classes 0-2, 2-4, 4-6, and 6+ feet. In
Standard night-light alligator survey route followed on Lake
Griffin from 1981-1986.
Figure 1.
1600 m
.--- 1600 m
LAKE
GRIFFIN
Standard night-light alligator survey route followed on Lake
Jessup from 1981-1986.
Figure 2.
N
U3
"
Figure 3. Standard night-light alligator survey route followed on Lake
Apopka from 1981-1986.
LAKE APOPKA
* 3400
Figure 4. Standard night-light alligator survey route followed on Lake
Woodruff from 1981-1986.
LAKE
OODRUFF
- .1700 m
cases where only eye reflections were seen and no reliable estimate of
size could be obtained the observation was recorded as "unknown". Eye
reflections seen at the outer limits of the spot light (approximately
300 m beyond the transect line) were recorded as "not approached". For
analytical purposes, "unknown" and "not approached" categories were
divided into the 1 foot categories based on the proportions of animals
occurring in those known size classes. Total length estimates were based
on the relationship that snout-length in inches equalled total length in
feet. To calibrate estimates, several alligators were sized by sight
and then caught and measured prior to beginning surveys.
Log-transformed count data were analyzed for trends in size
composition (while accounting for the effects of water level as a
covariable) by dividing the number of known size alligators counted
during night surveys in each of 3 size classes (2-6, 4-6, and 2+ ft.) by
the total number of known-size alligators counted and transforming the
resulting proportions by an arcsin transformation. Regression analyses
were conducted on those transformed proportions to test the hypothesis
that size class composition changed during the study.
Evaluation of the 3 size classes was emphasized for those
categories in which harvested cohorts were likely to be represented.
The 2+ foot category was evaluated to better understand total population
response to other demographic and environmental factors.
Cost-Benefit Ratio of Egg and Hatchling Collection
Assessments of alligator egg and hatchling removal provided a
measure of the economic and biological viability of each procedure.
Evaluation of expenditures were based on actual incurred expenses.
Personnel time was estimated from work loads and average times for
completion of those jobs. A relative salary level of 6.00/hr remained
constant in the analysis of egg and hatchling removal. The salary level
was based on average projected needs for professional and technical
services. Salaries ranged from volunteers to individuals making
approximately $30.00/hr. Airboat expenses were based on average use of
airboat engine types. For example, boats with larger
engines were required during egg collection to traverse difficult
habitat, thereby increasing hourly costs over those used for hatchling
removal.
The information developed for this analysis was based on the 1982
hatchling removal on Lakes Griffin and Apopka (all nests on Lake Jessup
were flooded in that year) and the 1986 egg removal for Lakes Griffin ,
Apopka, and Jessup. Because of the experience level of personnel, those
collections reflect the most efficient strategy for both situations and
would be considered an accurate appraisal of minimum costs associated
with this study. These values should not be used to directly estimate
costs of potential management programs but instead are an estimate of
relative costs among habitat types, nesting densities, and collection
methods.
RESULTS & DISCUSSION
Early age-class removal
Over the course of this study, 4120 hatchlings and 17,039 fertile
eggs were removed from the 3 study areas. Lake Griffin was the most
productive lake, resulting in 2,161 hatchlings during 1981 and 1982 and
Personnel time was estimated from work loads and average times for
completion of those jobs. A relative salary level of 6.00/hr remained
constant in the analysis of egg and hatchling removal. The salary level
was based on average projected needs for professional and technical
services. Salaries ranged from volunteers to individuals making
approximately $30.00/hr. Airboat expenses were based on average use of
airboat engine types. For example, boats with larger
engines were required during egg collection to traverse difficult
habitat, thereby increasing hourly costs over those used for hatchling
removal.
The information developed for this analysis was based on the 1982
hatchling removal on Lakes Griffin and Apopka (all nests on Lake Jessup
were flooded in that year) and the 1986 egg removal for Lakes Griffin ,
Apopka, and Jessup. Because of the experience level of personnel, those
collections reflect the most efficient strategy for both situations and
would be considered an accurate appraisal of minimum costs associated
with this study. These values should not be used to directly estimate
costs of potential management programs but instead are an estimate of
relative costs among habitat types, nesting densities, and collection
methods.
RESULTS & DISCUSSION
Early age-class removal
Over the course of this study, 4120 hatchlings and 17,039 fertile
eggs were removed from the 3 study areas. Lake Griffin was the most
productive lake, resulting in 2,161 hatchlings during 1981 and 1982 and
8,349 fertile eggs from 1983-1986. Lakes Jessup and Apopka were less
productive resulting in the collection of 317 and 491 hatchlings, and
6,203 and 2,487 fertile eggs, respectively.
Inconsistencies in the collection techniques and variability in
habitat type among lakes probably resulted in underestimation of total
production during some years. Consequently, actual removal levels did
not always approach the targeted 50% level.
Nest Production and Success
Estimates of total nest production on all study lakes were
generally lower during 1981 and 1982 than all other years (Table 1).
Nest production and nest survival trends are considered herein only for
those years (1983-1986) in which reliable and consistent data were
collected from helicopter surveys.
Minimum Total Nesting -- Nesting estimates for Lake Griffin ranged
from a low of 95 during the 1984 drawdown (Fig 5) to a high of 166
during 1983 (Table 1). We considered the latter estimate to be the most
reliable assessment of total nesting effort because aerial survey
techniques had been standardized and sufficient capture-recapture work
was conducted during the fall to quantify pods not associated with
aerially observed nests. Therefore, total nesting estimates during 1981
and 1982 may be underestimated by as much as 36% if total nesting effort
is assumed to be constant from the first year of removal through the
third year (juvenile removal would not have a sudden impact on the
nesting segment of the population). Estimates of total nesting for 1984
and 1985 probably were underestimated because insufficient
Table 1. Minimum total alligator nesting effort and removal rates on
Lakes Griffin, Jessup, Apopka, Woodruff and Paynes Prairie,
1981-1986.
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capture-recapture efforts resulted in underestimations of hidden nests.
Decreased nesting during low water (1984) probably resulted from
inaccessibility of traditional nesting locations and increased
physiological stress due to crowding and competition for food. However,
nesting attempts recovered in 1985 and 1986 (Table 1) and no decreasing
trends were found in juvenile size classes,indicating that short-term
negative impacts on the population was minimal.
Nesting estimates on Lake Jessup ranged from 74-129 during
1983-1986. Because canopy cover was absent in the major nesting areas
we feel confident that these estimates are accurate counts of actual
nesting effort. Variations in nesting from year-to-year likely can be
attributed to natural fluctuations in the proportions of breeding adult
females.
In years where reliable helicopter surveys were utilized to
estimate total nest production on Lake Apopka, average nesting effort
was 42 per year. A review of the 1981 data however, indicate that the
number of pods found increased when intensive hatchling removal efforts
were utilized. Although 81% of the estimated nests were found in this
manner during 1981, we could not assume that similar proportions of
nests were missed on successive years because of potential reproductive
failures. We do, however, recognize that total nesting estimates from
1983 1986 may be underestimated due to insufficient manpower to
implement capture-recapture efforts during that time.
Similarly, total nest production on control area Lake Woodruff
probably underestimated of actual nesting because of limited
capture-recapture efforts. These data, however, do likely represent
more reliable trend information because capture efforts were consistent
from year-to-year, unlike capture-recapture efforts on treatment areas.
Nest Depredation--Nest depredation varied among study areas as well
as among years within areas (Table 2). Variation among lakes likely was
the result of differing predator population densities and
behavior(principally racoons, Procyo Lotor), and accessibility of nests
to predators, whereas differences within lakes probably were related to
water level changes.
Yearly depredation rates were highest on Lake Woodruff (x= 33.5%,
sd = 14.0) and lowest on Lake Griffin (x = 12.3; sd = 5.7) (Table 2).
Rates averaged 17.0% (sd = 7.6) and 20.5% (sd = 7.5) for Lakes Jessup
and Apopka, respectively (Table 2). The highest depredation rates for
Lakes Griffin and Jessup occurred during low water periods of 1984 and
1986, respectively (Fig. 5, 6). Jennings et al. (1985) found that
alligator nest depredation patterns were clumped when water levels were
low, suggesting that low water levels increase marsh accessibility by
raccoons. In contrast, although Lake Woodruff experienced similar
hydrological fluctuations as Lake Jessup (Fig 6), depredation rates
appeared independent of water level.
Though speculative, these differences are best explained by
variations in available raccoon habitat, density and behavior. Cagle
(1949) proposed that certain populations of raccoons "learn" what foods
are available and then seek specific items. If certain raccoon
populations have thus "learned" when alligator nests are available and
selected for them, one might expect some wetland systems to suffer
higher rates of depredation. We know nothing of densities of raccoons
on any of the areas but suspect that even if habitats were similar
Table 2. Depredation rates of alligator nest on Lakes Griffin,
Jessup, Apopka, and Woodruff, from 1981-1986.
Year Number Nests Depredated Depredation Rate (%)
Lake Woodruff
1981 6 33
1982 3 11
1983 13 30
1984 14 33
1985 7 19
1986 27 52
Lake Griffin
1981 4 8
1982 -
1983 14 7
1984 26 21
1985 18 9
1986 23 12
Lake Jessup
1981 8 31
1982 -
1983 19 14
1984 24 19
1985 5 12
1986 46 23
Lake Apopka
1981 6 7
1982 -
1983 4 13
1984 9 22
1985 5 24
1986 12 23
Maximum water levels (NGVD) experienced on Lake Jessup for
October 1980-September 1986 (U. S. Geological Survey,
1982-1986).
Figure 6.
7nr
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mnr
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imr
Nvr-126 i
inr
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River, size of the watershed, and geophysical variations. Clearly,
evaluation of the effects of these parameters on alligator nest success
will require additional and more precise information.
Flooding of alligator nests on Lake Apopka (R = 16.0%, sd = 14.9)
was not related to water level changes (Fig 7). These data, however,
must be interpreted carefully. Because flooding estimates were based
only on aerially observed nests, the potential existed to bias final
nest fate estimations based on subsamples. On Lake Apopka, this meant
that nests located in the relatively open (little canopy cover) marsh
community were more likely to be observed than nests located under the
heavy canopy cover of the bottomland hardwoods. Furthermore, we
expected nest flooding to be higher in the marsh habitat because nests
usually had poor substrate support and decomposed rapidly (pers. obs.).
Conversely, no flooded nests were located in the bottomland hardwood
association throughout this study. Comparison of habitat-specific nest
flooding (Table 4) clearly indicate that estimates of nest flooding
based on aerially observed nests overestimates total nest flooding
rates. Though this phenomenon may be unique to Lake Apopka, future
evaluation of nest flooding (and depredation) on other wetlands should
incorporate habitat specific monitoring where 2 or more distinct
habitats exist. The impact that flooding had on total nest success was
minimal on Lake Griffin, ranging from 2-11%.
Night-Light Counts
Analyses of night-light counts indicated no significant trends in
any of the size classes for alligators on Lake Woodruff (Fig. 9) or Lake
Griffin (Fig. 10, Table 5). As expected, none of the size class
productive areas in terms of alligator production. It is
likely that the majority of Florida wetlands are less
productive. Therefore, harvest levels for these areas-should
be set at more conservative levels until potential long term
impacts have been examined.
4. Ranching management programs should employ both hatchling and
egg removal. The decision of which technique to be employed
will depend upon the habitat, nesting density and
accessibility, and target rates.
5. Research efforts should be directed toward investigating egg
viability in major drainage basins of the state.
Specifically, comparisons of egg viability data may provide a
method of evaluating wetland quality and could potentially be
used as an early indicator of contaminant loading. Immediate
studies on the dramatic problems on Lake Apopka should be given
high priority.
Table 3. Flooding rates of alligator nests on Lakes Griffin,
Jessup, Apopka, and Woodruff, from 1981-1986.
Year Number Nests Flooded Flooding Rate(%)
Lake Woodruff
191 0 0
1982 0 0
1983 0 0
1984 3 7
1985 0 0
1986 1 2
Lake Griffin
1981 1 2
1982 -
1983 9 11
1984 1 2
1985 8 11
1986 0 0
Lake Jessup
1981 2 8
1982 17 100
1983 0 0
1984 30 60
1985 34 83
1986 7 5
Lake Apopka
1981 1 7
1982 -
1983 4 27
1984 0 0
1985 5 36
1986 3 10
Table 4. Comparison of alligator nest flooding rates in marsh'and
bottomland hardwood habitats on Lake Apopka from 1983-1985.
Hardwoods
number nests/flooded nests
12/0 (0%)
10/0 (0%)
23/0 (0%)
Marsh
number nests/flooded nests
29/4 (14%)
24/0 ( 0%)
23/5 (22%)
Year
1983
1984
1985
River, size of the watershed, and geophysical variations. Clearly,
evaluation of the effects of these parameters on alligator nest success
will require additional and more precise information.
Flooding of alligator nests on Lake Apopka (X = 16.0%, sd = 14.9)
was not related to water level changes (Fig 7). These data, however,
must be interpreted carefully. Because flooding estimates were based
only on aerially observed nests, the potential existed to bias final
nest fate estimations based on subsamples. On Lake Apopka, this meant
that nests located in the relatively open (little canopy cover) marsh
community were more likely to be observed than nests located under the
heavy canopy cover of the bottomland hardwoods. Furthermore, we
expected nest flooding to be higher in the marsh habitat because nests
usually had poor substrate support and decomposed rapidly (pers. obs.).
Conversely, no flooded nests were located in the bottomland hardwood
association throughout this study. Comparison of habitat-specific nest
flooding (Table 4) clearly indicate that estimates of nest flooding
based on aerially observed nests overestimates total nest flooding
rates. Though this phenomenon may be unique to Lake Apopka, future
evaluation of nest flooding (and depredation) on other wetlands should
incorporate habitat specific monitoring where 2 or more distinct
habitats exist. The impact that flooding had on total nest success was
minimal on Lake Griffin, ranging from 2-11%.
Night-Light Counts
Analyses of night-light counts indicated no significant trends in
any of the size classes for alligators on Lake Woodruff (Fig. 9) or Lake
Griffin (Fig. 10, Table 5). As expected, none of the size class
Maximum water levels (NGVD) experienced on Lake Apopka from
October 1980-September 1986 (U. S. Geological Survey,
1982-1986).
Figure 7.
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II
co ON ) 1
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co In
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inp
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Inr
NVP-86L
in-
NVP-Z861
inr
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Figure 9. Alligator population trends on Lake Woodruff based on
night-light surveys conducted from 1981-1986.
L.MY\n. -vv Un.uLJrr
(2-4 Ft. Size Classes)
1981 1982 1983 1984 1985 1986
LAKE WOODRUFF
(2-6 Ft. Size Classes)
1981 1982 1983 1984 1985 1986
LAKE WOODRUFF
(>'2 Ft. Size Classes)
1982 1983 1984 1985
Year
250-
200
ID
0
* 100
150
*
-- Adj. Counts
-0- Est. Trend
*-- Adj. Counts
--l Est. Trend
V250:
c
o 200'
U
< 100,
50
--- Adj. Counts
-8- ELt Trend
Figure 10.
Alligator population trends on Lake Griffin based on
night-light surveys conducted from 1981-1986.
LAKE GRIFFIN
(2-4 Ft. Size Closses)
Year
LAKE GRIFFIN
(2-6 Ft. Size Classes)
-+- Adj. Counts
-- Est. Trend
LAKE GRIFFIN
(>2 Ft Size Classes)
-4- Adj. Counts
- Est. Trend
-+- Adj. Counts
-8- Est. Trend
3180--
1980
1100'
3 900
l00.
o
, oo.
=700
G00.
Year
1988
Table 5. Analyses of night-light survey data for evaluation of
trends in the 2-4, 2-6, and 2 feet size classes on
Lakes Griffin, Jessup, Apopka, and Woodruff, from
1980(1)-1986.
2-4 feet
t(P)
Lake
2-6 feet
t(P)
2 feet
t(P)
Lake Griffin 0.349(0.7376) 0.062(0.9524) 0.556(0.5955)
Lake Apopka -5.182(0.008) -6.078(0.0003) -5.913(0.0004)
Lake Jessup 1.519(0.1725) 2.152(0.0684) 3.090(0.0176)
Lake Woodruff 1.663(0.1403) 1.733(0.1267) 1.665(0.1400)
categories were affected on our non-harvested control area. Stable
population numbers on Lake Griffin suggested that recruitment into the
2-6 foot size classes remained constant. Trends on Lake Jessup
indicated significant increases in animals>2 feet (Fig.11). Analyses of
trends for animals in the 2-4 and 2-6 ft. size classes indicated only
slight increases (Table 5), suggesting the overall population increase
probably was attributed to increases in the numbers of alligators>6
feet. Although animals larger than 6 feet probably have not directly
been affected by the removal treatment (eg. they do not belong to
cohorts hatching after 1981) their increase is difficult to explain.
Because the number of animals in the 2-6 ft size classes increased only
slightly over the past 6 years it is unlikely that the observed increase
in alligators>6 feet is to be a function of animals maturing and
entering the larger size classes. More likely, large alligators were
emigrating from Lake Monroe to Lake Jessup via the St. John's River.
Poaching also may have resulted in a larger scale movement of animals
than would be expected naturally. If poaching was an important source
of adult mortality, then the movement of new animals into those empty
territories may have resulted in a net increase in large alligators.
Alternatively, if the number of large alligators (>6ft) had been reduced
by poaching it is possible that higher survival was experienced by those
animals just approaching maturity because of reduced competition from
mature animals.
Analyses of trend data for Lake Apopka indicate significant
decreases in population numbers (Fig 12, Table 5). That decreases were
identified in all size classes (including> 6 ft) indicates that the
removal treatment was not responsible for the observed population
declines.
Figure 11. Alligator population trends on Lake Jessup based on
night-light surveys conducted from 1981-1986.
(2-4 Ft. Size Classes)
-- Adj. Counts
--- Est. Trend
1983 1984 1985 1986
LAKE JESSUP
(2-6 Ft. Size Closses)
-- Adj. Counts
--- Est. Trnd
1981 1982 1983 1984 19815 I9g
Yeor
SLAKE JESSUP
(>2 Ft. Size Closses)
- Adj. Counts
-e- Est. Trend
1982 1983 1984
o00
o
3001
S200
100
100
1981
'V
- 500-
o
U -
so
0
4
"o 00 r
.0'
a
300-
V
S6o00
0
o
u
Figure 12.
Alligator population trends on Lake Apopka based on
night-light surveys conducted from 1980-1986.
LAKE APOPKA
(2-4 Ft. Size Classes)
1981 1082 1983
Year
1984 1985 1988
LAKE APOPKA
(2-6 Ft. Size Classes)
80 1981 1982 1083
Year
1984 1985 19I
LAKE APOPKA
(>2 Ft. Size Classes)
- Adj. Count*
-e- Et. Trend
6
-- Adj. Counts
-- Est. Trend
1980 1981 1982 1983
Year
1984 1985 Io8
-- Adj. Counts
- E- Est. Trend
1000-
r -
8001
0
Uo
0
" 400-
200-
O"
1200
1000
c
boo
0
,.)
O
-600
400
Cost-Benefit Ratio of Collecting Wild Production
The relative cost per collected hatchling in 1982 was $11.45 on
Lake Griffin and $21.97 on Lake Apopka (Table 6). Egg collection costs
per viable hatchling during 1985 were $3.34, $9.96, and $15.80 on Lakes
Griffin, Jessup, and Apopka, respectively (Table 7).
Difference in hatchling costs between Lakes Griffin and Apopka
likely was the result of lake size, habitat accessibility, and total
nest production. Lake Apopka is approximately 3 times as large as Lake
Griffin and produced only 1/3 as many nests over a much broader area,
resulting in a proportionately greater search effort and thus a greater
cost per hatchling. Further, pod locations often were in inaccessible
areas which required numerous revisits to completely remove the entire
pod. Although pod locations were generally accessible on Lake Griffin,
high water levels often precluded total capture of an entire pod.
It became evident that in systems with relatively dense nesting (e.g.
Griffin) collection efficiency could be maximized by collecting
hatchlings from pods that were most accessible while leaving those that
remained deep in the marsh.
Although hatchling costs derived from egg collection techniques
were lower on all lakes than costs from hatchling collection, there were
large differences among lakes. These differences primarily were due to
differential nesting densities, nest site accessibility, nest
observability and egg hatchability. On Lake Griffin, where nesting
rates were high and dense and located within 50 m of the shoreline,
efficient use of aircraft and ground crews resulted in the lowest costs
per hatchling. Further, habitat type (thus nest observability) also
influenced the cost of egg removal. For example, aerial surveys are
Table 6. Estimated costs of hatchlings derived from the collection of
juvenile alligators, on Lakes Griffin and Apopka during 1982.
COST OF HATCHLING COLLECTION (1982)
LAKE GRIFFIN
Personnel
search time
travel time
planning
Travel
Gasoline (autos)
Airboats
Misc. equip.
(wheatlights, tongs, tags)
398 hrs @ 6.00/hr
71 hrs @ 6.00/hr
100 hrs/3 lakes @
10.00/hr
70 days @ 50.00/hr
104 hrs @ 22.00/hr
Total cost
Total cost/hatchling ($9810.00/857)
LAKE APOPKA
Personnel
search time
travel time
planning
Travel
Gasoline (autos)
Airboats
Misc. equip.
(wheatlights, tong, tags)
32 hrs @ 6.00/hr
12 hrs @ 6.00/hr
100 hrs/3 lakes @
10.00/hr
8 days @ 50.00/day
16 hrs @ 22.00/hr
Total/cost
$1824.00
Total cost/hatchling ($1824.00/83)
2388.00
426.00
333.00
3500.00
500.00
2288.00
375.00
$9810.00
$11.45
192.00
72.00
333.00
400.00
100.00
352.00
375.00
$9810.00
$21.97
Table 7. Estimated costs of hatchling alligators derived from egg
collections, on Lakes Griffin ,Jessup, and Apopka during 1986.
COST OF EGG COLLECTION (1986)
LAKE GRIFFIN
Personnel
air time
ground crews
travel time
planning
Travel
Gasoline(autos)
Helicopter
Airboats
Misc. equip.
16.9 hrs @ 6.00/hr
127.5 hrs @ 6.00/hr
36 hrs @ 6.00/hr
33.3 hrs @ 10.00/hr
9 people X 4 days @ 50.00/day
16.9 hrs @ 125.00/hr
5 boats 13.5 hrs @ 25.00/hr
Total cost
Total cost/hatchling ($6468.40/1936)
LAKE JESSUP
Personnel
air time
ground crew
travel time
planning
Travel
Helicopter
Airboats
Misc. equip.
10.3 hrs
90 hrs @
36 hrs @
33.3 hrs
@ 6.00/hr
6.00/hr
6.00/hr
@ 10.00/hr
9 people X 4 days @ 50.00/day
10.3 hrs @ 125.00/hr
5 boats 9.0 hrs @ 25.00/hr
Total cost
Total cost/hatchling ($5696.30/572)
LAKE APOPKA
Personnel
airtime
ground crews
travel time
planning
Travel
Helicopter
Airboats
Misc. equip.
2.5 hrs @ 6.00/hr
48 hrs @ 6.00/hr
16 hrs @ 6.00/hr
33.3 hrs @ 10.00/hr
8 people x 4 days @ 50.00 day
2.5 hrs @ 125/hr
4 boats 6 hrs @ 25.00/hr
Total cost
Total cost/hatchling ($3777.00/239)
101.40
765.00
216.00
333.00
1800.00
120.00
2112.50
1687.50
333.00
$6468.40
$ 3.34
61.86
540.00
216.00
333.00
1800.00
1287.50
1125.00
333.00
$5696.30
-- 9.96
15.00
288.00
96.00
333.00
1800.00
312.50
600.00
333.00
$3777.00
$ 5.80
inefficient along wooded shorelines such as on Lake Apopka.
Approximately one-half of the estimated production was aerially observed
on a small remnant marsh bordering the north shore. Of these nests,
only 25-50% were accessible by ground crews in any given year. The
remaining production occurred on the western and southern shores in
bottomland hardwood associations. Nests were difficult to observe from
the air due to the thick canopy and less efficient ground searches were
initiated to locate nests.
More importantly, egg hatchability was very critical in
determining final cost per viable hatchling. Artificially incubated
Lake Griffin eggs had a mean hatching rate of 68.0%, much higher than
Lakes Jessup (42.5%) or Apopka (23.5%). Thus, more hatchlings per unit
effort results from collections on Lake Griffin than on Lakes Jessup or
Apopka.
Finally, initial capital expenditures for organizational planning
(approximately $1,000) and miscellaneous equipment ($1,000) represented
7.2% and 38.9% of total hatchling costs for juvenile removal on Lakes
Griffin and Apopka, respectively. Similar costs involved in egg removal
efforts represented 10.2% (Lake Griffin), 48.1% (Lake Apopka), and 11.6%
(Lake Jessup) of the total cost per hatchling. Due to the experimental
nature of this project these costs probably reflect a larger portion of
the actual costs per hatchling than would be expected with operational
harvest programs. Though the actual costs likely would be lower, the
facts remain that costs would vary with factors such as nest density,
accessibility, and hatchability.
Nesting Parameters
Artificial incubation of wild alligator eggs provided an
opportunity to compare clutch size, fertility and hatchability rates
among central Florida lakes (Woodward 1985). Although this information
was not initially considered imperative to the evaluation of prescribed
removal rates it has ultimately provided valuable information on
potential reproductive failures on Lake Apopka as well as early warnings
of reproductive problems on Lake Jessup.
From 1984 1986 total clutch size on Lake Apopka ranged from
44.8 46.3 (Tf= 45.3) and was not significantly different (P > 0.05)
than Lakes Griffin (x = 45.4) or Jessup (X = 45.8). Hatching rates,
however, ranged from 20.0%-25.0%, and were significantly lower (P = <
0.05) than Lakes Griffin (66.6% 70.3%) and Jessup (38.0% 69.0%).
Interestingly, an average of only 5.8, 8.5, and 5.8 alligators
successfully hatched from each Apopka nest containing fertile eggs
during those years, even though fertility rates (72.0-74.0) were not
significantly different (P> 0.05) than Lakes Griffin and Jessup.
Additionally 35.0%, 15.2%, and 13.0% of all visited nests contained only
infertile eggs from 1984 1986, respectively. These data strongly
suggest that declining population densities on Lake Apopka are due to
reproductive failures and developmental problems and not removal levels.
A convenient explanation for these reproductive failures would
center around the possibility of a large influx of environmental
contaminants entering the system via insecticide spraying of orange
groves and vegetable farms. Preliminary results of alligator eggs
analyzed at the Patuxent Wildlife Research Center of the U.S. Fish and
Wildlife Service indicate that p,p'-DDE, p,p'-DDD, and dieldrin were
consistently found in all eggs and cis-Chloradane, trans-Nonachlor,
cis-Nonachlor, toxaphene, and PCB were found in some, but not all eggs
(Table 8). Ogden et al. (1973) and Hall et al. (1979) found many of the
same organochlorines in the eggs of American crocodiles in south
Florida, but did not speculate on the impact on crocodilian reproductive
success. The levels of most organochlorines reported in the latter two
studies were much lower than levels reported here. Specifically, Ogden
et al. (1973) and Hall et al. (1979) reported average DDE and Dieldrin
levels of 1.84 and 1.19 and 0.01 and 0.02 ppm respectively.
DDE levels in Lake Apopka eggs (T6= 6.1 ppm) were significantly
higher (P< 0.05) than levels in Lake Griffin (x = 0.82 ppm) and Lake
Okeechobee (x = 1.2 ppm). These elevated DDE levels were high enough to
cause reproductive failures in the most sensitive avian species (Hickley
and Anderson 1968, Blus et al. 1974). Levels of all other
organochlorines did not appear to be high enough to cause reproductive
problems in alligators based on the literature for birds (G. Heinz pers.
comm.). No differences were detected in thickness or shell quality of
alligator eggs among lakes. Although these results are inconclusive
and based on rather small sample sizes, there is sufficient evidence to
warrant substantial research effort on the effects of organachlorine
contamination on alligator reproduction in Lake Apopka.
Additional hypotheses developed to explain the poor reproductive
success of alligators on Lake Apopka include population demographics and
stress. It has been suggested that the majority of the reproductive
segment may be approaching senescence and are therefore incapable of
producing viable clutches. This argument, however, does not explain why
the number of juvenile alligators (>6 ft.) continues to decline.
Table 8. Results of analysis for presence of 12 organochlorines (ppm)
in 6 alligator eggs taken from Lake Apopka during 1984.
SAMPLE NUMBER
Compound 1 2 3 4 5 6
p,p'-DDE 8.1 7.2 7.1 7.6 3.7 3.2
p,p'-DDD 0.96 0.56 1.0 0.99 0.80 0.66
p,p'-DDT -
Dieldrin 0.30 0.27 0.48 0.57 0.11 0.09
Hept. epoxide -
Oxychlordane -
cis-Chlordane 0.14 0.12 0.09 0.08
trans-Nonachlor 0.16 0.11 0.20 0.09
cis-Nonachlor 0.13 0.09 -
Endrin -
Est. Toxaphene 0.11 0.14 0.12 -
Est. PCB 0.36 0.84 -
-not detected
Alternatively, stress, related to food availability and quality, also
has been considered as a limiting factor in reproductive success and
juvenile survival. Unfortunately, no comprehensive and consistent data
are available for evaluating fluctuations in prey base populations.
Conclusion
The removal of 50% annual alligator production over a 6 year period
on 3 central Florida lakes did not significantly decrease population
size structures. On Lake Jessup significant increases were found in the
2+ ft. size classes, while on Lake Griffin no significant changes were
found in any size classes. Lake Apopka experienced significant
(P < 0.05)declines in all size classes, but this phenomenon is more
likely due to currently unexplained reproductive failures and not the
early age-class harvest. No significant change (P > 0.05) in size
structure was found for the control area, Lake Woodruff.
Cost-benefit ratios for the hatchling egg collections varied
between techniques and among lakes. Hatchling removal is most efficient
in wetland systems with dense nesting effort and distinct water-marsh
interfaces. Similarly, egg collections are most efficient in wetland
areas containing dense nesting concentrations and in areas with
indiscrete water-marsh interfaces. A monetary comparison of both
techniques indicate that egg collection is most efficient when large
proportions of a population are to be managed. When very conservative
limited removal rates are prescribed, however, hatchling collection
becomes more cost effective because of the high start-up costs of egg
collection. For example, if a quota of 100 hatchlings (as opposed to 25
clutches of eggs) were set for a given system, it would be much more
efficient to simply allow a trapper to remove them.
The biological impacts of hatchling and egg removal appear
equivalent. Although hatchling removal allows natural mortality of
nests and hatchlings to act upon production, egg removal obviates this
mortality and results in a greater number of animals collected.
An effect of habitat type on nest success was not demonstrated.
Low water levels during nest incubation, however, did precipitate higher
depredation rates by raccoons in specific habitat locales (Jennings
1986.)
Juvenile growth and survival rate estimates could not statistically
be analyzed due to insufficient recapture data. Growth rate models will
be pursued when additional recapture data are available. Survival rate
estimation for the American alligator is probably impractical because of
sample size requirements.
Recommendations
The objective of this research project was to evaluate the impacts
of removal on alligator populations. Although we were unable to fully
address all facets, the data gained provided sufficient information to
identify the short term responses of alligator populations to a 50%
removal of annual production. Based on these findings and the questions
stimulated by this investigation the following recommendations are
suggested.
1. A 50% removal treatment should continue on all 3 study areas
for at least an additional 5 years. Long-term trends in
alligator populations cannot adequately be evaluated during a
one 5-year study, and any lapse in treatment may confound
interpretation of future demographic impacts.
2. Additional monitoring, including nest surveys, night-light
surveys and capture-recapture efforts, should continue on all
study areas. These data will add to baseline information
already available on growth rates. Further, such
monitoring also will provide a mechanism to ensure that any
long term impacts are detected and quantified.
3. That 50% annual removal has had no apparent negative impact on
3 central Florida lakes does not imply that 50% removal rates
can be sustained on all Florida wetlands. In contrast, the
3 treatment lakes now under study represent several of the most
productive areas in terms of alligator production. It is
likely that the majority of Florida wetlands are less
productive. Therefore, harvest levels for these areas should
be set at more conservative levels until potential long term
impacts have been examined.
4. Ranching management programs should employ both hatchling and
egg removal. The decision of which technique to be employed
will depend upon the habitat, nesting density and
accessibility, and target rates.
5. Research efforts should be directed toward investigating egg
viability in major drainage basins of the state.
Specifically, comparisons of egg viability data may provide a
method of evaluating wetland quality and could potentially be
used as an early indicator of contaminant loading. Immediate
studies on the dramatic problems on Lake Apopka should be given
high priority.
Literature Cited
Blus, L. J., B. S. Neely, Jr., A. A. Belisle, and R. M. Prouty. 1974.
Organochlorine residues in Brown Pelican eggs: relation to
reproductive success. Environ. Pollut. 7:81-91.
Cagle, F.R. 1949. Notes on the raccoon, Procyon lotor megalodus Lowery.
J. Mammal. 30:45-47
Campbell, H.W. 1972. Ecological or phylogenetic interpretations of
crocodilian nesting habits. Nature 238:404-405.
Canfield, D.E., Jr. 1981. Chemical and trophic state characteristics
of Florida Lakes in relation to regional geology. Sch. For. Res.
and Cons., Univ. of FL., Gainesville. 444 pp (Mimeo).
Deitz, D.C., and T.C. Hines. 1980. Alligator nesting in north-central
Florida. Copeia 1980:249-258.
Ferguson, M.W.J. 1981. Extrinsic microbial degradation of the
Alligator eggshell. Science 214:1135-1137
Hall, R. J., T. E. Kaiser, W. B. Robertson, Jr., and P. C. Patty. 1979.
Organochlorine residues in eggs of the endangered American
Crocodile (Crocodylus acutus). Bull Environ. Contam. Toxicol.
23:87-90.
Hickey, J. J. and D. W. Anderson. 1968. Chlorinated hydorocarbons and
eggshell changes in raptorial and fish-eating birds. Science.
162:271-273.
Hines, T.C. 1979. The past and present status of the alligator in
Florida. Proc. Ann. Conf. S.E. Assoc. Game and Fish Comm.
33:224-232.
Jacobsen, T., and J.A. Kushlan. 1986. Alligator nest flooding in the
southern Everglades: A methodology for management. Pages 153-174
in Proc. 7th working meeting I.U.C.N. Crocodile specialists Group,
Caracas, Venezuela. 446 pp.
Jennings, M.L., H.F. Percival and C.L. Abercrombie. 1986. Habitat
variables and spacing patterns affecting the nesting success of the
American alligator in central Florida. M.S. Thesis. Univ. of FL,
Gainesville. 33 pp.
Joanen, T. 1969. Nesting ecology of alligators in Louisiana. Proc.
Ann. Conf. S. E. Assoc. Game and Fish Comm. 23:141-151.
Johnson, D. H. 1979. Estimating nest success: the Mayfield method and
an alternative. Auk 96:651-661.
National Res. Council. 1983. Crocodiles as a resource for the tropics.
National Academy Press, Washington D.C. 59 pp.
Ogden, J. D., W. B. Robertson, Jr., G. E. Davis, and T. W. Schmidt.
1974. Pesticides, polychlorinated biphenols and heavy metals in
upper food chain levels, Everglades National Park and vicinity.
National Park Service Management Report. 27pp.
Rose, M. 1982. Crocodile management and husbandry in Papua New Guinea.
Pages 148-163 in Proc. 6th working meeting I.U.C.N. Crocodile
specialists Group, Victoria Falls, Zimbabwe. 219 pp.
Wood, J.M., A.R. Woodward, S.R. Humphrey, and T.C. Hines. 1985. Night
counts as an index of American alligator population trends. Wildl.
Soc. Bull. 13:262-272.
Woodward, A.R. 1985. (in press) Time of collection of wild alligator
eggs in Florida for ranching. in Proc. Fourth Annual Alligator
Production Conf. Gainesville, Florida.
Woodward, A.R. and W.R. Marion. 1978. An evaluation of factors
affecting night-light counts of alligators. Proc. Ann. Conf.
Southeast. Assoc. Fish and Wildl. Agencies. 32:291-302.
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