Natural exposure of coastal river otters to mercury: relation to age, diet, and survival

We evaluated effects of location (i.e., Jackpot Bay, a naturally contaminated site, and Herring Bay, reference site), diet as determined by stable isotopes, and age on mercury concentrations in individual river otters (Lontra canadensis) from Prince William Sound, Alaska, USA. We also investigated the effects of mercury accumulation on survival of river otters from these two locations. Our results indicated that mercury concentrations in fishes from Jackpot Bay were significantly higher than those in fishes from Herring Bay and those in pelagic fishes. In addition, a predominant intertidal fish diet in both areas influenced the accumulation of mercury concentrations in otters. Concentrations of mercury in fur of river otters from Jackpot Bay were significantly higher than those of animals from Herring Bay. Nonetheless, we did not detect significant differences in survival between otters inhabiting the two areas, suggesting that this natural contamination was not high enough to impair survival. Our ability to investigate the effects of various factors such as location, diet composition, and age on mercury accumulation and subsequent survival of individuals offers an example for a link between individual-based captive studies and population-level field investigations.