Project Title: An Assessment of Population Structure and Movements of Hawksbill Sea Turtles (Eretmochelys imbricata) in Palm Beach County Waters
Project Manager: Larry Wood
Organization: Busch Wildlife Sanctuary (Non-Profit Organization)
Grant Amount: $24,915.00
Completion Date: 2009-04-20
Summary: This study represents the first effort to survey Palm Beach County coral reefs (Florida, USA) for hawksbill turtles (Eretmochelys imbricata). Individual turtles will be hand-captured at depth using SCUBA, retained on a vessel for the collection of morphometric data, tag placement, photographs, tissue sampling for DNA analysis, and blood sampling for gender determination. This study is the first in the State to focus solely on hawksbills, and will continue to provide much needed data on the abundance, ecology, and movements of this critically endangered species. To date, 95 hawksbills have been captured during 81 field days (typically two-tank dive charters). Frequent sightings of un-tagged turtles within the study area support the continuation of the sampling effort.
Results: The relative abundance of hawksbills on these reefs remains surprisingly high, and the results of the tasks performed remain extremely valuable to hawksbill conservation efforts in Florida. To date, a total of 122 hawksbills have been captured in 143 days diving. The catch per unit effort has been calculated at just under 1 capture per in-water hour. The in-water surveys have revealed that the hawksbills of the area are primarily juveniles and sub-adults, confirming that the study area represents developmental habitat. The median straight carapace length (n=122) is 56.6 cm, with a maximum of 82.3 cm and a minimum of35.7 cm. Of the five turtles that exceeded 70 cm straight carapace length, 3 are presumed to be females and 2 are known to be males based on tail length measurements. A total of 25 turtles have been re-captured, revealing an average straight length measurement increase of 2.4 cm per year. It is unclear whether all of these individuals will remain in the area throughout their developing years, but it preliminary data suggest that at least some do. Should that be the case, based on the growth rate data so far, individual hawksbills may be residents of the area for approximately 15-20 years to grow from an average of forty to eighty cm straight carapace length. The results of the mtDNA analyses suggest that the majority of the hawksbills in Palm Beach County originate in Mexico, however a total of seven haplotypes have been identified, one from as far away as Costa Rica. Though results from additional samples are still pending, the Florida population has shown an unusual ratio of Caribbean haplotypes, and we are working to finish the remaining samples and report the findings as appropriate. (Author: Larry Wood)