Characterizing the foraging ecology of leatherback turtles (Dermochelys coriacea) using stable carbon and nitrogen isotopes of eggshells

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Stable isotopes are useful tools for discerning information regarding the foraging ecology of far-ranging animals like sea turtles. Isotope signatures of prey items are integrated into the turtles? tissues in a characteristic manner, and in the case of nesting females, eggshell isotopic signatures can provide insight into the trophic status and foraging locations of the adult females. By sampling eggshells from nesting beaches, one can obtain a unique, wide-range perspective that might not be observed by sampling turtles directly within foraging areas. In the present study, leatherback turtle eggshells were collected from 21 different nests on the nesting beach in Jamursba Medi, Papua, Indonesia in the Western Pacific in July 2003. Habitat samples, including particulate organic matter, krill, gelatinous organisms, squid, and small fish were collected with dip nets and bongo tows in the Eastern Pacific, off the west coast of the United States. Eggshell ?13C values were similar for all eggshell samples (-13.2 ? 1.2 ?). However, there was a dichotomy in ?15N values, with 62% of the eggshells in the 9.2?-10.8? range and 38% in the 12.5?-14.5? range. Comparing these values with the ?15N values of habitat samples analyzed in this study and others as well as with information on Pacific-wide nitrogen fixation/denitrification patterns, suggests that these two ?15N groupings represent animals foraging in the Western Pacific and Eastern Pacific, respectively. These data are consistent with satellite telemetry data and suggest that ?15N isotope analysis can be an effective, non-invasive method to gain knowledge about turtle foraging locations that may prove useful in conservation efforts.

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