Increased nesting, good survival and variable site fidelity for leatherback turtles in Florida, USA

Abstract

Despite facing serious threats of extinction in the Eastern Pacific, the leatherback turtle (Dermochelys coriacea) appears to be thriving in the Atlantic basin based on increasing nest counts at several rookeries. In particular, Florida’s nest numbers have been increasing by 10.2% per year since standardized counts began in 1979. The US Recovery Plan for leatherbacks calls for vital rates and population parameters to be determined for the three leatherback rookeries under US jurisdiction: St. Croix (USVI), Puerto Rico, and the east coast of Florida. Based on mark-recapture data gathered over eleven years, we determined important population parameters for nesting female leatherbacks at Juno Beach, one of the most densely nested beaches in Florida. Average annual survival was 88.9%. The average female nesting population size for Juno Beach is estimated at 100±41 individuals each season; statewide we expect the estimate to be higher. The average remigration interval was 2.7±1.0years. In addition, we report observed clutch frequency (2.1±1.4 clutches/year), estimated clutch frequency (4.4±1.1 nests/year), and observed internesting period (10.2±1.3days between nests). The probability of observing an individual female at least once during the season was 73.0%, likely due to variable site fidelity, even though sea turtles do exhibit natal homing. Using opportunistic observations at additional beaches, we found that 72 females observed nesting within the Juno Beach study area were also observed nesting outside the study area. Thirty-three individuals laid clutches both inside and outside the survey area within a single season; these nests were separated by as much as 463.5km. Although the population in Florida is relatively small compared to other rookeries throughout the Western Atlantic, it is increasing at such a rapid pace that it has the potential to become more important regionally, thereby contributing to the abundance of leatherbacks in the Atlantic.