UC Santa Cruz

Environmental contaminants are a continued threat to marine wildlife because they are globally dispersed, bioaccumulate in top predators, and can disrupt physiological pathways, thus leading to adverse health effects. For adult marine mammals, the main source of contaminants is through their diet, therefore foraging behavior, including geographic location, foraging depth, and prey type, may exacerbate or mitigate contaminant exposure. Fluctuating body condition can also significantly affect contaminant concentrations in multiple tissues and thus temporally influence individual toxicological risk.

My dissertation provides an extensive analysis of the assimilation of persistent organic pollutants (POPs) and mercury into the mesopelagic-foraging northern elephant seal. My research integrates foraging behavior (movements, diving, and stable isotopes), physiology (reproductive or molting state and measurements of general body condition), and demographics (age and sex), to understand how these factors influence contaminant dynamics.

Northern elephant seals, Mirounga angustirostris, spend the majority of their lives at sea foraging in the mesopelagic (200 – 1000 m depths) North Pacific Ocean, hundreds to thousands of kilometers from the coastline of North America. Such remoteness creates challenges to understanding the ecosystem where they forage. However, elephant seal life history brings them to shore predictably twice each year for breeding and molting, at which time we can sample their tissues and attach or recover electronic tags to quantify movements and diving behavior.

Every elephant seal I sampled had detectable concentrations of PCBs, PBDEs, organochlorine pesticides and mercury, demonstrating that POPs and mercury are pervasive in the food webs of northern elephant seals. For both POPs and mercury, I showed varying levels of bioaccumulation in elephant seals related to foraging behavior across a large region of the northeast Pacific, indicating that certain regions and depths pose a heightened exposure risk of contaminants to marine predators. However, the relationship between foraging behavior and contaminant bioaccumulation differed among individual compounds. Because predators integrate contaminants from their foraging areas, geographical variability in predator contaminant concentrations may be a useful indicator of the ecotoxicological risk of these contaminants to cryptic or threatened marine predators that live in deep ocean food webs of the North Pacific Ocean.