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

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.

Modeling and mapping isotopic patterns in the Northwest Atlantic derived from loggerhead sea turtles

“…Satellite-tracked individuals often constitute training data for the development of models to geographically assign individuals of unknown origin (e.g., Jaeger et al 2010, Ceriani et al 2012, Seminoff et al 2012. However, to apply telemetry assignment models with confidence, it is critical to assess their performance by conducting external validation.…”

“…Sea turtle, in particular loggerhead (Caretta caretta), migratory connectivity has been increasingly studied using a combination of satellite telemetry and stable isotope analysis (Hatase et al 2002, Zbinden et al 2011, Ceriani et al 2012, Pajuelo et al 2012, Seminoff et al 2012). Loggerheads are generalist consumers feeding on a variety of food items, mostly benthos when on the continental shelf (Hopkins-Murphy et al 2003, but see McClellan et al 2010.…”

“…Each female from a nesting aggregation typically forages in one of several geographically distinct foraging grounds (Schroeder et al 2003, Girard et al 2009, Hawkes et al 2011, Ceriani et al 2012, Foley et al 2013. Telemetry revealed that loggerheads nesting in east central Florida, the largest nesting aggregation in the Atlantic, follow distinct migratory routes associated with three foraging grounds (Ceriani et al 2012, Foley et al 2013: (1) a seasonal shelf-constrained north-south migratory pattern along the northeast USA coastline, (2) a year-round residency in the South Atlantic Bight (SAB), mainly in waters adjacent to the breeding area, and (3) a year-round residency in southern foraging grounds such as the Bahamas and southeast Gulf of Mexico. Individual females appear to show fidelity to both nesting and feeding areas throughout their adult life (Miller et al 2003, Broderick et al 2007, Tucker et al 2014.…”

“…64 cm (Bjorndal et al 2000), is better understood than many other marine species, which makes them good candidates to assess existing geographic assignment methods and develop new approaches (e.g., see Wunder 2012 for overview of geographic assignment models). Ceriani et al (2012) examined the use of stable isotope analysis to infer foraging areas used by adult female loggerheads during the non-breeding season. Here, we include a larger number of loggerheads equipped with satellite tags and juveniles sampled at foraging grounds across a broader geographic area.…”

Sea Turtles in Florida's Atlantic Waters

“…We completed a thorough review Ehrhart et al, 2007;Hawkes et al, 2007Hawkes et al, , 2011Arendt et al, 2012a,b,c), satellite telemetry (Blumenthal et al, 2006;Girard et al, 2009;Mansfi eld et al, 2009;Arendt et al, 2012a,b,c;Ceriani et al, 2012), shipboard surveys (Bresette et al, 2010), aerial surveys (Fritts et al, 1983;Schroeder and Thompson, 1987;Epperly et al, 1995Epperly et al, , 2002McClellan, 1996;Witzell and Azarovitz, 1996;Henwood and Epperly, 1999;Goodman et al, 2007), stable isotopes (Reich et al, 2007a, b;Ceriani et al, 2012), and bycatch records (Thompson et al, 1991;Epperly et al, 2002). Mark-recapture via fl ipper or pit tagging provides start and end point data demarking some travels (Meylan, 1995;Schmid and Witzell, 1997;Witzell, 1998;Williams and Frick, 2008).…”