Correlates of mercury in female river otters (Lontra canadensis) from Nova Scotia, Canada

Abstract

Mercury (Hg) can reach toxic concentrations in aquatic habitats, sometimes as a consequence of human activity. Mercury can have deleterious effects, particularly in piscivorous mammals in which it bioaccumulates. Furs from trapper-provided female otter (Lontra canadensis) carcasses in Nova Scotia were analyzed for total Hg. Concentrations of total Hg in fur samples averaged 25 µg/g dry weight, ranging from 1.4 to 137 µg/g; 20 µg/g is the fur concentration at which toxic effects are expected. Mercury concentrations were greater in otters from watersheds with bedrock substrates known to contain more available Hg, from otters trapped farther inland, and from otters trapped on watersheds with hydroelectric dams. Otter reproductive potential was measured by counting the number of blastocysts in reproductive tracts. Tooth annuli were used to age otters. Reproductive potential was not related to Hg concentration, nor was Hg concentration related to age. In a general linear model, 53% of variation in fur Hg was explained by underlying bedrock, distance from the coast at which otters were trapped, and presence/absence of a hydroelectric dam. The proportion of juveniles in a population did not differ relative to bedrock Hg concentration, but was lower on watersheds with hydroelectric dams. Because we found no evidence of reduced reproductive potential from greater Hg concentrations, the low proportion of juveniles suggests that Hg reduced juvenile survival, although our evidence is circumstantial.