Stable isotope analyses of cold-stunned Kemp’s ridley (Lepidochelys kempii) sea turtles at the northern extent of their coastal range

Abstract

Kemp’s ridley (Lepidochelys kempii) sea turtles strand on Cape Cod, USA (41.894757°N, − 70.289372°W) as water temperatures drop in November, but little is known about their pre-stranding ecology. Carbon and nitrogen stable isotope values of soft tissues (liver and muscle) and scutes (anterior edge and interior) from cold-stunned individuals (n = 26) sampled from 2006 to 2008 were used to assess general patterns of local and early life-history habitat use. After adjusting for trophic discrimination, anterior scute carbon and nitrogen isotope values (n = 11) representative of recent feeding were lower and higher, respectively, than potential offshore prey but similar to many local neritic prey and sea turtle-derived isoscapes for New England waters. These results combined with a significant increase in δ15N values for scute edge relative to scute interior samples representative of early life history suggest local foraging prior to stranding. Interior scute δ13C and δ15N values mirrored Gulf of Mexico isoscapes, consistent with early life-history foraging near nesting habitat. Liver (rapid) and muscle (slow turnover) isotope offsets differed among individuals (n = 15), suggesting that the cold-stunned population does not have a homogenous migratory and/or trophic history. Liver tissue showed evidence of starvation-induced δ15N alteration, which could bias interpretation of isotope data from rapid turnover tissues. Further stable isotope analyses including complementary tracers and techniques will improve our knowledge of this poorly understood assemblage at the northern extent of the species’ coastal range. Such data will aid managers in preserving foraging habitat and prey resources in New England waters that may become increasingly important if Kemp’s ridley distribution shifts polewards with climate change.