Project Title: Clutch Frequency of Sea Turtles Residing on the Southwest Florida Shelf, Year 2
Project Manager: Tony Tucker
Organization: Mote Marine Laboratory (Non-Profit Organization)
Grant Amount: $28,520.00
Completion Date: 2009-02-13
Summary: To derive a more rigorous determination of clutch frequency, it is now possible to use satellite tags to evaluate how many nests a female may deposit within a season. The methods require that females be instrumented early in the nesting season and followed through the reminder of all internesting intervals until a final nest and then a post-reproductive migration. Apart from the study on Casey Key that targets early nesters, other satellite tracking studies on Florida loggerheads have applied tags at the end of the nesting season (July-August) and would therefore provide underestimates of annual fecundity. This second year of study proposes to determine clutch frequency of loggerheads at the two primary nesting beaches for loggerheads in the Gulf of Mexico. Satellite tags as well as standard Inconel flipper tags and PIT tags will be attached to nesting female loggerheads at either Casey Key or Manasota Key during May. Females will be tracked through the remainder of the nesting season to determine clutch frequency and site fidelity. Other valuable research byproducts related to conservation will be the determination of internesting movement, nest site fidelity, exposures levels to red tide, and other risks faced during the internesting and post-nesting movements. By deploying tags early in May, a more accurate determination of clutch frequency will be obtained. The methodological approaches are suited to any of Florida's rookeries so will provide data that are broadly representative for the loggerheads of peninsular Florida, but are ideally suited to beaches that also conduct simultaneous night time tag patrols, such as occur on Manasota and Casey.
Results: New estimates of clutch frequency and site fidelity for loggerhead sea turtles (Caretta caretta) were derived by satellite telemetry in the eastern Gulf of Mexico. Satellite telemetry allowed tracking of females that shifted to other locations away from a beach with nightly monitoring staff. Clutch frequency for 34 tracked females tracked in three nesting seasons ranged from 2 to 8 nests per season, with a modal value of 6 nests. The observed clutch frequency of 2.1 nests was lower than the actual clutch frequency of 5.5 nests per female determined by satellite tracking. Site fidelity ranged from 1.9 km to 109.1 km for all nests deposited by an individual within a season. Females with higher clutch frequency were larger females but also ones with higher site fidelity. Whenever population estimates of adult females are derived from nest counts, rather than empirically derived estimates of individual female fecundity, a significant conclusion is that fecundity underestimation results in population overestimates. Correction factors derived from this study suggest that current population estimates for Western Atlantic loggerheads may be substantially overestimated, perhaps by factors of 32%. (Author: Dr. Tony Tucker)
Read an article published in the Marine Turtle Newsletter based on this research: Eight Nests Recorded for a Loggerhead Turtle Within One Season