Term of Award

Winter 2001

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

David C. Rostal

Committee Member 1

Thane Wibbels

Committee Member 2

Ann E. Pratt

Committee Member 3

John W. Parrish

Abstract

The loggerhead turtle (Caretta caretta) is a threatened species throughout its range. Major nesting colonies occur in Florida, while smaller nesting colonies range up into the Carolinas and Virginia. However, the majority of research on this species has been conducted in Florida. Our overall understanding of the nesting populations on the barrier islands in Georgia is mainly limited to number of nests laid and number of females observed on select beaches. This method has proven problematic in estimating adult populations due to underestimating female nesting fecundity. Plasma steroid levels and ultrasonography were used to determine the population trends and nesting patterns for female C. caretta along Georgia's barrier islands. The reproductive status of nesting C. carettawas assessed at Wassaw and Blackbeard Island National Wildlife Refuges, Georgia during the 2000 and 2001 nesting seasons. Plasma testosterone and estradiol levels were observed to decline throughout the season with each successive nesting attempt. Data collected from nesting C. caretta in Georgia indicates that females are capable of producing 6 nests per season with an average of 5.2 nests per female. This increase in nesting fecundity has implications regarding adult female population estimates. These results also support the observation that nesting females may be utilizing multiple islands throughout the season.

Nesting has been monitored on several of Georgia's barrier islands for over 30 years. Management practices have been implemented to protect nests and increase hatching success. Recent research on temperature-dependent sex determination, population genetics, and migratory movement patterns in other species support the view that further research in Georgia is required to understand the contribution of these smaller nesting colonies to the Western Atlantic loggerhead population. Information from Florida demonstrates that the major nesting colonies produce 90% females, while colonies in North Carolina produce mostly males. Are the nesting colonies in Georgia essential for producing males and if so, what influence has nest relocation played on naturally occurring sex ratios? Temperature profiles throughout incubation and critical periods for sex determination were evaluated using Hobo ® temperature data loggers and hatchling gonadal histology. Data was also collected to assess possible effects of nest relocation, hatchling size, and nest hatching success in Georgia. Results of this study did not reveal a discemable difference in incubation temperatures and hatchling size between in situ and relocated nests. By collecting these data, we have been able to address questions regarding the biological role of nesting colonies on barrier islands and management needs for Georgia's loggerheads.

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