Inferring Foraging Areas of Nesting Loggerhead Turtles Using Satellite Telemetry and Stable Isotopes

Simona A Ceriani,Daniel R Evans,John F Weishampel,Llewellyn M Ehrhart,James D Roth

doi:10.1371/journal.pone.0045335

Simona A Ceriani, Daniel R Evans + Show 3 more

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https://doi.org/10.1371/journal.pone.0045335

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Abstract

In recent years, the use of intrinsic markers such as stable isotopes to link breeding and foraging grounds of migratory species has increased. Nevertheless, several assumptions still must be tested to interpret isotopic patterns found in the marine realm. We used a combination of satellite telemetry and stable isotope analysis to (i) identify key foraging grounds used by female loggerheads nesting in Florida and (ii) examine the relationship between stable isotope ratios and post-nesting migration destinations. We collected tissue samples for stable isotope analysis from 14 females equipped with satellite tags and an additional 57 untracked nesting females. Telemetry identified three post-nesting migratory pathways and associated non-breeding foraging grounds: (1) a seasonal continental shelf–constrained migratory pattern along the northeast U.S. coastline, (2) a non-breeding residency in southern foraging areas and (3) a residency in the waters adjacent to the breeding area. Isotopic variability in both δ13C and δ15N among individuals allowed identification of three distinct foraging aggregations. We used discriminant function analysis to examine how well δ13C and δ15N predict female post-nesting migration destination. The discriminant analysis classified correctly the foraging ground used for all but one individual and was used to predict putative feeding areas of untracked turtles. We provide the first documentation that the continental shelf of the Mid- and South Atlantic Bights are prime foraging areas for a large number (61%) of adult female loggerheads from the largest loggerhead nesting population in the western hemisphere and the second largest in the world. Our findings offer insights for future management efforts and suggest that this technique can be used to infer foraging strategies and residence areas in lieu of more expensive satellite telemetry, enabling sample sizes that are more representative at the population level.

Highlights

The movement of organisms in space and time defines their interaction with the environment and, constitutes a central aspect of their ecology and evolutionary biology [1]
Two females took up year-round residency in the Great Bahamas Bank, just south of the Bahamian island of Andros, one female dwelled in the shallow waters of the Gulf of Mexico immediately west of the Florida/Georgia border through Pinellas County (Florida) Keys, while the last individual resided in the SE Gulf of Mexico off the SW Florida coast
The Carr NWR hosts approximately 25% of all the nests laid by the North West Atlantic (NWA) loggerhead Florida Peninsular Recovery Unit, which in turn makes up the greatest majority of the NWA female population

Summary

Introduction

The movement of organisms in space and time defines their interaction with the environment and, constitutes a central aspect of their ecology and evolutionary biology [1]. The regular seasonal movement of individuals, often from a breeding location to a nonbreeding location and back [2], is widespread in nature. Many species travel across thousands of kilometers in regular movements that constitute some of the most spectacular natural phenomena on the planet (e.g. Arctic tern [3], monarch butterfly [4], salmon [5], sea turtles [6], humpback whales [7]). Migratory connectivity describes the movement of individuals between breeding and nonbreeding areas. For many species the latter areas have not been identified [2]

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