MEPS 537:265-276 (2015)  -  DOI: https://doi.org/10.3354/meps11452

ABSTRACT: Individual variation in diet composition has important evolutionary, ecological, and conservation implications. However, few studies of marine turtles have examined long-term foraging behavior of individuals. Using stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values from blood plasma, we examined long-term variation in resource use of 27 juvenile loggerhead turtles Caretta caretta captured multiple times in North Carolina between 2001 and 2010. Seven turtles displayed a marked increase in δ¹⁵N values consistent with a shift from oceanic to neritic habitat. These turtles, which we designated as ‘recruits’, had initial straightline carapace lengths (SCL) and δ¹⁵N values at first sampling that were significantly lower (p = 0.007 and p < 0.0001, respectively) than the remaining 20 ‘resident’ turtles. For the resident group, the influence of SCL on δ¹³C (p = 0.02) and δ¹⁵N (p = 0.05) values was significant. Individual effects on δ¹³C values were also significant (p < 0.001), indicating that foraging patterns vary among individuals; however, individual effects were not significant for δ¹⁵N (p = 0.07). Stable isotope niche width calculations suggested that residents were consistent in resource selection over time, and individuals were specialized in resource use relative to the population. Also, the resident population was more specialized than generalized in resource use, and stable isotope mixing (MixSIAR) model results suggest their diet is largely comprised of horseshoe crabs Limulus polyphemus. These findings improve understanding of the foraging ecology of juvenile loggerhead turtles, and highlight the importance of examining the long-term diet composition of individuals.

KEY WORDS: Caretta caretta · Individual specialization · Niche width · Resource use · Stable isotopes