Tracking Juvenile Kemp's Ridley Sea Turtles With Stable Isotopes

Abstract

Every fall, juvenile sea turtles become trapped in Cape Cod Bay and strand as the cooling waters lowers their metabolism into a hypothermic state called cold-stunning. Kemp's ridleys are the most endangered sea turtle species and account for the majority of cold-stunned sea turtles in Massachusetts. Stable isotope analysis has been used to track migratory animals including other sea turtles species except for Kemp's ridleys. For marine life, the ratios of δ13C and δ15N correlate to latitude and distance from shore, respectively. Since tissues do not incorporate stable isotopes at the same rate, an individual's migration route can be identified by analyzing the same isotopes in different tissues. Skin and whole blood samples from fifteen deceased Kemp's ridleys that were recovered in November and December 2017 were analyzed and compared to existing isoscapes of the northwestern Atlantic Ocean to identify their summer feeding grounds. The skin sample ratios showed that the Kemp's ridleys were likely feeding off the coast of the mid-Atlantic states in June through July. The whole blood samples put the sea turtles in Georges Bank, southeast of Cape Cod, in August through September, but it is possible that the turtles were feeding further north in the Gulf of Maine. The creation of a Gulf of Maine isoscape would help determine just how far north juvenile Kemp's ridley sea turtles migrate, identifying important feeding habitat for a vulnerable life stage.