Sea turtle hatchling production from Florida (USA) beaches, 2002-2012, with recommendations for analyzing hatching success

B Brost,L Ehrhart,B Witherington,E Leone,D Bagley,A Meylan

doi:10.3354/esr00653

Abstract

We measured sea turtle hatchling production on 16 sea turtle nesting beaches (219.6 km) in Florida (USA) from 2002 to 2012. A standard protocol was used to sample 19 701 loggerhead Caretta caretta, 3809 green turtle Chelonia mydas, and 664 leatherback Dermochelys coriacea nest contents, representing all Florida nesting beaches. We assessed (1) annual variation in hatching (hatched eggs/total eggs) and emergence (emerged hatchlings/total eggs) successes, (2) annual hatchling production, and (3) sources of egg and hatchling mortality. Emergence success rates were extrapolated to all Florida sea turtle nesting beaches using means weighted by each beach’s nesting contribution. Weighted mean emergence success was 51.6% for loggerheads, 50.0% for green turtles, and 38.7% for leatherbacks. These estimates represent survivorship to the time hatchlings emerge from the nest. The estimated annual mean number of hatchlings produced on Florida beaches during the study period was 3 528 180 loggerheads (SD = 1 155 701), 568 098 green turtles (SD = 327 156), and 33 014 leatherbacks (SD = 17 574). Beach erosion from storms and nest predation by mammals were the principal identified sources of egg and hatchling mortality. Average emergence success ranged from 38.8 to 65.0% between years and 41.8 to 61.7% between study beaches, suggesting that a single sample year or location would not adequately represent a sea turtle population in demographic analyses of multiple year classes. We provide recommendations for analyzing hatching success and present a method of analysis that allows the inclusion of partially depredated nests. These nests are typically excluded because the original clutch size and the number of eggs removed by predators may not be known.

Highlights

Sea turtle nesting on Florida (USA) beaches occurs at a globally significant scale
We evaluated data from each sample nest for errors in inventory counts and other inconsistencies and excluded data that met any of 5 criteria: (1) the nest could not be located at inventory time, and the surveyor did not know the nest’s fate; (2) notes indicated that the nest had been given special treatment because it was a sample nest; (3) the nest experienced partial washout from beach erosion during incubation; (4) a major disturbance occurred after hatchlings should have emerged but before the inventory was conducted; or (5) the nest had been relocated
We calculated hatching and emergence success, and estimated hatchling production based on inven

Summary

Introduction

Sea turtle nesting on Florida (USA) beaches occurs at a globally significant scale. Florida hosts the largest number of nesting loggerhead turtles Caretta carettaPublisher: Inter-Research · www.int-res.comEndang Species Res 27: 53–68, 2015 erbacks Dermochelys coriacea (Stewart et al 2011). Sea turtle nesting on Florida (USA) beaches occurs at a globally significant scale. Florida hosts the largest number of nesting loggerhead turtles Caretta caretta. Because of the importance of Florida to sea turtle nesting, estimates of hatchling production from Florida provide important demographic rates for models that measure conservation success and assess recovery actions. Sea turtle populations are considered under multiple listings to be at risk of extinction (Stewart & Johnson 2006, Witherington et al 2006a,b), but significant gaps in knowledge concerning each population prevent a complete understanding of their demographic status. We address survival rates for the earliest sea turtle life stages — eggs and hatchlings in the nest — focusing on the number of hatchlings that emerge from the nest unaided.

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Conclusion