Factors Affecting Hatch Success of Hawksbill Sea Turtles on Long Island, Antigua, West Indies

Mark Allan Ditmer,Seth Patrick Stapleton,Richard K.F Unsworth

doi:10.1371/journal.pone.0038472

Mark Allan Ditmer, Seth Patrick Stapleton + Show 1 more

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https://doi.org/10.1371/journal.pone.0038472

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Abstract

Current understanding of the factors influencing hawksbill sea turtle (Eretmochelys imbricata) hatch success is disparate and based on relatively short-term studies or limited sample sizes. Because global populations of hawksbills are heavily depleted, evaluating the parameters that impact hatch success is important to their conservation and recovery. Here, we use data collected by the Jumby Bay Hawksbill Project (JBHP) to investigate hatch success. The JBHP implements saturation tagging protocols to study a hawksbill rookery in Antigua, West Indies. Habitat data, which reflect the varied nesting beaches, are collected at egg deposition, and nest contents are exhumed and categorized post-emergence. We analyzed hatch success using mixed-model analyses with explanatory and predictive datasets. We incorporated a random effect for turtle identity and evaluated environmental, temporal and individual-based reproductive variables. Hatch success averaged 78.6% (SD: 21.2%) during the study period. Highly supported models included multiple covariates, including distance to vegetation, deposition date, individual intra-seasonal nest number, clutch size, organic content, and sand grain size. Nests located in open sand were predicted to produce 10.4 more viable hatchlings per clutch than nests located >1.5 m into vegetation. For an individual first nesting in early July, the fourth nest of the season yielded 13.2 more viable hatchlings than the initial clutch. Generalized beach section and inter-annual variation were also supported in our explanatory dataset, suggesting that gaps remain in our understanding of hatch success. Our findings illustrate that evaluating hatch success is a complex process, involving multiple environmental and individual variables. Although distance to vegetation and hatch success were inversely related, vegetation is an important component of hawksbill nesting habitat, and a more complete assessment of the impacts of specific vegetation types on hatch success and hatchling sex ratios is needed. Future research should explore the roles of sand structure, nest moisture, and local weather conditions.

Highlights

Hawksbill sea turtle (Eretmochelys imbricata) populations have declined by more than 80% from historical levels [1,2], leading to their designation as critically endangered by the IUCN (2011)
Management agencies and conservation organizations have adopted a number of practices to improve hatch success by replanting native beach vegetation, safeguarding nesting beaches, and relocating nests that are in danger of inundation from tides and rain [7,8], predation [9,10], or humancaused disturbances [11]
We analyzed and modeled the hatch success of 652 nests deposited by 198 individual hawksbill sea turtles spanning 6 nesting seasons using 12 temporal, environmental, and reproductive covariates (Table 1)

Summary

Introduction

Hawksbill sea turtle (Eretmochelys imbricata) populations have declined by more than 80% from historical levels [1,2], leading to their designation as critically endangered by the IUCN (2011). While initiatives focused on later sea turtle life stages may have a greater impact on species recovery [3], hatch success is recognized as an important component for growth and recovery of marine turtle populations in empirical studies [4,5] and simulations [6]. Sea turtles (both adult females and their offspring) are most accessible at nesting beaches, thereby providing the opportunity to directly impact their conservation at these life stages. Management agencies and conservation organizations have adopted a number of practices to improve hatch success by replanting native beach vegetation, safeguarding nesting beaches, and relocating nests that are in danger of inundation from tides and rain [7,8], predation [9,10], or humancaused disturbances [11]. Better management of vegetation and nesting beaches can further buffer against some impacts of climate change [12], and improved placement of relocated nests may increase the probability of nest success [13]

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