Habitat models and assessment of habitat partitioning for Kemp’s ridley and loggerhead marine turtles foraging in Chesapeake Bay (USA)

G Lockhart,A DiMatteo,S Barco

doi:10.3354/esr01168

Abstract

Understanding the spatial distribution of a species is required to enact effective conservation. Complications to effective conservation can arise when the distributions of multiple target species are non-overlapping. Conservation efforts meant to protect one species may shift threats into the distribution of another species. Two species of marine turtle, loggerhead Caretta caretta and Kemp’s ridley Lepidochelys kempii, are common seasonally in Chesapeake Bay, a large estuary on the US east coast. Both species are protected under the US Endangered Species Act and face spatially complex threats in the region. We created habitat suitability models for these 2 species to inform conservation efforts in the region and explore the extent of overlap between their distributions. Argos satellite tags were deployed on 24 Kemp’s ridley and 10 loggerhead turtles to record animal locations within the Bay. Boosted regression tree models were created for each species using presence-only animal locations, predicting suitable habitat within the Bay. Habitat for Kemp’s ridley turtles was predicted in shallow, coastal areas of the southern Bay as well as in brackish areas of rivers. Loggerhead turtle habitat was predicted to extend farther north than Kemp’s ridley habitat and was generally found in deeper areas of the middle Bay. There is some evidence that these 2 species are partitioning habitat. Any conservation measures adopted to conserve marine turtles in the Chesapeake Bay should consider the habitat of both species holistically to avoid shifting impacts from one species to another.

Highlights

Conservation measures for widely ranging marine fauna often focus on protecting critical life stages or activities such as breeding, foraging, or migrating (Corrigan et al 2014, Lascelles et al 2014, Calambokidis et al 2015)
We explored the possibility that these 2 sea turtle species were partitioning their habitat by comparing the outputs of the 2 habitat suitability models
State−space modeling hierarchical state−space model (hSSM) for both species performed acceptably, converging with 80 000 posterior samples for the Kemp’s ridley model and 50 000 samples for the loggerhead model. Both models used 10 000 samples as an adaptation phase, and a span parameter of 0.2. hSSM diagnostics for both models indicated that Monte Carlo Markov chains were mixing, that parameter estimates converged based on the Gelman-Ruben shrink factor (Gelman & Rubin 1992, Brooks & Gelman 1998), and that autocorrelation between chains was acceptably low

Summary

Introduction

Conservation measures for widely ranging marine fauna often focus on protecting critical life stages or activities such as breeding, foraging, or migrating (Corrigan et al 2014, Lascelles et al 2014, Calambokidis et al 2015). The effectiveness of these conservation measures is dependent on understanding the distribution of a species during these activities, allowing for targeted intervention at appropriate spatial and temporal scales (Norse 2010, Davies et al.2012, Guisan et al 2013). Implementation of conservation measures for one species can shift deleterious effects from one species to another (Salas & Gaertner 2004, Barrows et al 2005, Abbott & Haynie 2012). By imposing fishing closures in one area to avoid bycatch of a protected species, that fishing effort may shift to where another protected species resides.

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Results

Conclusion