Objectives:

Evaluate movement and distribution patterns of sea turtles in our series of study sites

in The Bahamas. This objective includes the questions of where do the turtles come

from, how long are they resident in these sites, and where do they go when they

leave.

Collect data that will allow us to develop techniques to compare habitat quality and to

serve as a foundation for studies of the role of green turtles in seagrass ecosystems.

Evaluate models for estimating growth rates and carrying capacities for sea turtles

based on our data from a long-term study of immature green turtles in the southern

Bahamas.  (Document has 7 pages.

Bjorndal, Karen A.

Bolten, Alan B.

English

Aquatic Commons

MIGRATION AND HABITAT USE 
OF SEA TURTLES IN THE BAHAMAS 
RWO 166 
Final Report to 
Florida Cooperative Fish and Wildlife Research Unit 
University of Florida 
Research Work Order 166 
December 1998 
Karen A. Bjorndal and Alan B. Bolten 
Archie Carr Center for Sea Turtle Research 
University of Florida 
Gainesville, Florida 3261 1 
MIGRATION AND HABITAT USE 
OF SEA TURTLES IN THE BAHAMAS 
Objectives: 
Evaluate movement and distribution patterns of sea turtles in our series of study sites 
in The Bahamas. This objective includes the questions of where do the turtles come 
from, how long are they resident in these sites, and where do they go when they 
leave. 
Collect data that will allow us to develop techniques to compare habitat quality and to 
serve as a foundation for studies of the role of green turtles in seagrass ecosystems. 
Evaluate models for estimating growth rates and carrying capacities for sea turtles 
based on our data from a long-term study of immature green turtles in the southern 
Bahamas. 
Results: 
All of the project objectives were met. Many results have been analyzed and presented in 
the publications listed below. The results of this project have also been presented at 
many international meetings, some of whlch are indicated below as publications in 
proceedings from those meetings. The success of this project is evident in the quality of 
the publications that are based on data collected during the completion of the objectives 
of this project. These manuscripts are either published, in press, or in review. The cover 
page and abstract of the manuscript that is in review are enclosed. 
Many of the results of Objective #1 have been analyzed and published (see below). 
However, some of results have not been analyzed because of the long lag times involved. 
Many green turtles, hawksbills, and loggerheads were tagged with standard flipper tags 
throughout The Bahamas Archipelago during this study, and we must await the recapture 
of these tagged animals before we can determine long-term residence times and 
movement patterns. Results of genetic analyses are not yet complete. When the genetic 
haplotypes for all sampled sea turtles have been determined, these results will be 
analyzed and published. 
Objective #2 has been successfully completed. We have developed techniques to mimic 
green turtle grazing in pastures of the seagrass Thalassia testudinum and to monitor 
changes in biodiversity and Thalassia productivity in these grazed plots. One of our 
graduate students, Kate Moran, will use these techniques for her doctoral research on the 
effects of green turtle grazing on the structure, function, and biodiversity of Thalassia 
ecosystems. 
The results of Objective #3 are contained in the manuscript now in review (cover page 
and abstract attached). We not only evaluated growth rates of immature green turtles in 
the southern Bahamas with a nonparametric regression model with five covariates, but 
we also estimated the carrying capacity of the Caribbean seagrass beds for green turtles 
based on our rates of seagrass intake in the southern Bahamas. 
Publications Based on Results from RWO 166 
Bjorndal, K.A. 1998. Model of the nutritional ecology of the green turtle. Page 13, C. 
Kirk (compiler), Proceedings of the Second Comparative Nutrition Society 
Symposium. CNS, Silver Spring, Maryland. 
Bjorndal, K.A. In press. Quantitative models of nutritional ecology. Proceedings of the 
International Conference on Turtles and Tortoises. California State University, 
Dominguez Hills, 30 July - 2 August 1998. 
Bjorndal, K.A. In press. Roles of sea turtles in marine ecosystems: nutritional ecology 
and productivity. In Proceedings of the 18th International Symposium on Sea 
Turtle Biology and Conservation, Mazatlan, Mexico. NOAA Technical 
Memorandum. 
Bjorndal, K.A. and A.B. Bolten. 1996. Developmental migrations of juvenile green 
turtles in the Bahamas. Pages 38-39 in J.A. Keinath, D.E. Barnard, J.A. Musick 
and B.A. Bell (compilers), Proceedings of the Fifteenth Annual Symposium on 
Sea Turtle Biology and Conservation. NOAA Technical Memorandum NMFS- 
SEFSC-387. 
Bjorndal, K.A. and A.B. Bolten. 1998. Hawksbill tagged in The Bahamas recaptured in 
Cuba. Marine Turtle Newsletter 79: 18- 19. 
Bjorndal, K.A. and A.B. Bolten. 1998. Hawksbill tagged in The Bahamas recaptured in 
Cuba. Bahamas Journal of Science 5:33. 
Bjorndal, K.A., A.B. Bolten, R.A. Bennett, E.R. Jacobson, T.J. Wronski, J.J. Valeski and 
P.J. Eliazar. 1998. Age and growth in sea turtles: limitations of 
skeletochronology for demographic studies. Copeia 1998:23-30. 
Bjorndal, K.A., A.B. Bolten, R.A. Bennett, E.R. Jacobson, T.J. Wronski, J.J. Valeski and 
P.J. Eliazar. In press. Limitations of skeletochronology for demographic studies 
in sea turtles. In Proceedings of the Seventeenth Annual Symposium on Sea 
Turtle Biology and Conservation, Orlando, Florida. NOAA Technical 
Memorandum. 
Bjorndal, K.A., A.B. Bolten and M.Y. Chaloupka. In press. Green turtle somatic 
growth: density dependence, regulation of developmental migrations, and regional 
differences. In Proceedings of the 18th International Symposium on Sea Turtle 
Biology and Conservation, Mazatlan, Mexico. NOAA Technical Memorandum. 
Bjorndal, K.A., A.B. Bolten and M.Y. Chaloupka. In review. Green turtle somatic 
growth model: evidence for density dependence. 
Bowen, B.W., A.L. Bass, A. Garcia-Rodriguez, C.E. Diez, R. van Dam, A.B. Bolten, 
K.A. Bjorndal, M.M. Miyamoto and R.J. Ferl. 1996. Origin of hawksbill turtles 
in a Caribbean feeding area as indicated by genetic markers. Ecological 
Applications 6566-572. 
Encalada, S.E., P.N. Lahanas, K.A. Bjorndal, A.B. Bolten, M.M. Miyarnoto and B.W. 
Bowen. 1996. Phylogeography and population structure of the Atlantic and 
Mediterranean green turtle Chelonia mydas: a mitochondria1 DNA control region 
sequence assessment. Molecular Ecology 5 :473-483. 
Lahanas, P.N, K.A. Bjorndal, A.B. Bolten, S.E. Encalada, M.M. Miyamoto, R.A. 
Valverde and B.W. Bowen. 1998. Genetic composition of a green turtle 
(Chelonia mydas) feeding ground population: evidence for multiple origins. 
Marine Biology 130:345-352. 
In Review 
Running Head: Green Turtle Growth Model 
Green Turtle Somatic Growth Model: Evidence for Density Dependence 
Karen A. ~jorndal', Alan B. ~olten',  and Milani Y. chaloupka2 
1 Archie Carr Center for Sea Turtle Research and Department of Zoology, University of Florida, 
PO Box 1 18525, Gainesville, FL 3261 1 USA 
2 Queensland Department of Environment, PO Box 155, Brisbane Albert Street, Queensland 
4002, Australia 
Address correspondence to: Karen A. Bjorndal 
Department of Zoology 
PO Box 118525 
Gainesville, FL 3 26 1 1 USA 
email: kab@zoo.ufl.edu 
tel: 352-392-5 194 
f a :  352-392-9166 
Bjorndal et al. -2 
ABSTRACT 
The green turtle, Chelonia mydas, is a circumglobal species and a primary herbivore in 
marine ecosystems. Over-exploitation as a food resource for human populations has resulted in 
drastic declines or extinction of green turtle populations in the Greater Caribbean. Attempts to 
manage the remaining populations on a sustainable basis are hampered by insufficient knowledge 
of demographic parameters. In particular, compensatory responses resulting from density- 
dependent effects have not been evaluated for any sea turtle population and thus have not been 
explicitly included in any population models. 
Growth rates of immature green turtles were measured during an 18-year study in Union 
Creek, a wildlife reserve in the southern Bahamas. We have evaluated the growth data for both 
straight carapace length (SCL) and body mass with nonparametric regression models that had one 
response variable (absolute growth rate) and five potential covariates: sex, site, year, mean size, 
and recapture interval. The SCL model of size-specific growth rates was a good fit to the data 
and accounted for 59% of the variance. The body-mass model was not a good fit to the data, 
accounting for only 26% of the variance. In the SCL model, sex, site, year, and mean size all had 
significant effects, whereas recapture interval did not. 
We used results of the SCL model to evaluate a density-dependent effect on somatic 
growth rates. Over the 18 years of our study, relative population density underwent a 6-fold 
increase followed by a 3-fold decrease in Union Creek as a result of natural immigration and 
emigration. Three lines of evidence support a density-dependent effect. First, there is a 
significant inverse correlation between population density and mean annual growth rate. Second, 
the condition index ( ~ ~ S S I S C L ~ )  of green turtles in Union Creek is positively correlated with 
mean annual growth rates and was negatively correlated with population density indicating that 
the green turtles were nutrient limited during periods of low growth and high population densities. 
Bjorndal et al.-3 
Third, the population in Union Creek fluctuated around carrying capacity during our study and 
thus was at levels likely to experience density-dependent effects that could be measured. 
We estimate the carrying capacity of pastures of the seagrass Thalassia testudinum, the 
major diet plant of the green turtle, as a range from 122 - 4439 kg green turtleslha or 16 - 586 
million 50-kg green turtles in the Caribbean. Because green turtle populations are probably 
regulated by food limitation under natural conditions, carrying capacity can serve as a baseline to 
estimate changes in green turtle populations in the Caribbean since pre-Columbian times and to 
set a goal for recovery for these depleted populations. 
Finally, we compare the growth finctions for green turtle populations in the Atlantic and 
Pacific oceans. Not only does the form of the size-specific growth hnctions differ between the 
two regions (monotonic declining in the Atlantic and nonmonotonic in the Pacific), but also small 
juvenile green turtles in the Atlantic have substantially higher growth rates than those in the 
Pacific. Research is needed to evaluate the causes of these differences, but our results indicate 
that demographic parameters should only be extrapolated with great caution between ocean 
basins. 
Key words: Australia; Bahamas; Chelonia mydas; carrying capacity; demography; density- 
dependent efect; growth models; growth rate; marine turtles; nonparametric regression; 
sustainable use. 
Key phrases: densitydependent effects on demographic processes; comparison of growth rates 
of green turtles in the Caribbean and PaciJc Ocean; estimation of carrying capacity; 
management of long-lived species; nonparametric regression model to evaluate continuous and 
nominal covariates; sources of variation in somatic growth rates; sustainable utilization of 
wi ldlve. 


Migration and habitat use of sea turtles in the Bahamas

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Migration and habitat use of sea turtles in the Bahamas

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