Use of DDTs and PCBs as chemical tracers in assessing the foraging locations and habits of northern elephant seals from Guadalupe Island (Mexico)

Abstract

Organochlorine contaminants (OCs) accumulate in top predators, reaching high levels associated with negative physiological effects. Measuring OCs is key for assessing the accumulation of their loads and evaluating the efficiency of contaminant regulations. Some OCs generate specific signatures in certain areas, which allow us to track potential movements and feeding habits of species. Thirtyfive blubber biopsies were taken from northern elephant seals (NES) during fall at Guadalupe Island (GI), Mexico, an important site for hauling-out, molting, and breeding. Biopsies were analyzed for dichlorodiphenyltrichloroethane and its metabolites (tDDTs), hexachlorobenzene, chlordanes, and total PCB congeners (tPCBs). tDDTs were higher in adults than in juveniles, suggesting age class-based bioaccumulation, related to time and differences in foraging and habitat use between age groups. Females had higher variability of OCs than males, attributed to multiple causes, including variation in the use of foraging grounds and niche segregation. The DDT:PCB ratios were the highest, showing similarity with the Palos Verdes (California) contaminant signature, suggesting the use of similar feeding areas in relation to juvenile NES from Southern California.