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.

Trapped river otters (Lontra canadensis) from central Saskatchewan differ in total and organic mercury concentrations by sex and geographic location

“…Other studies have found that the majority of Hg in fur/hair is OHg, highlighting the importance of fur as a receptacle of OHg from the body (Wolfe et al 1998;Evans et al 2000). THg concentrations in fur, liver, and kidney in otters collected from central Saskatchewan were comparable with concentrations in otters from unimpacted areas within Canada (Kucera 1983;Evans et al 1998Evans et al , 2000Mierle et al 2000;Klenavic et al 2008;Spencer et al 2011).…”

“…Other studies have shown similar trends in muscle (Strom 2008) and brain (Mierle et al 2000) tissue. In addition, THg in fur has been used to a greater extent than kidney Hg concentration when examining locational differences in other studies throughout North America (Mierle et al 2000;Yates et al 2005;Klenavic et al 2008;Spencer et al 2011). Using THg in fur was the preferred method for examining geographic differences and is a noninvasive, inexpensive way to monitor Hg over large geographic areas.…”

“…Due to biomagnification, otters may be exposed to greater concentrations of Hg than species feeding at lower trophic levels or those foraging on terrestrial prey. This, along with their wide distribution, makes otters ideal for studying Hg variation and impacts, both individually and at the landscape level (Kucera 1983;Mierle et al 2000;Fortin et al 2001;Yates et al 2005;Strom 2008;Stansley et al 2010;Spencer et al 2011). Moreover, there are studies showing adverse biochemical and organismal effects, and potentially population-level impacts on otters related to MeHg exposure (Wren 1991;Basu et al 2005;Sleeman et al 2010).…”

Mercury in Little Brown Bat (Myotis lucifugus) Maternity Colonies and Its Correlation with Freshwater Acidity in Nova Scotia, Canada

“…Mean fur THg concentrations (3.76 and 4.96 μg/g) were lowest for colonies located near the coast (Annapolis Royal and West Chezzetcook), which is consistent with trends observed in local freshwater otter populations, and may be associated with increased salt spray exposure. 31 Little brown bats at the two Cape Breton Island sites (Hunters Mountain and Christmas Island) had similarly low mean fur THg values (5.69 and 6.27 μg/g). Although these roosts are positioned further inland, they are located in close proximity to the Bras d'Or lakes, a large system of interconnected mixed freshwater and saltwater basins.…”

“…Moreover, the spatial distribution of fur THg concentrations in female little brown bats at the provincial scale resembles trends observed in Nova Scotia otters, which showed significantly higher fur THg concentrations in the southwest region of the province (with the exception of coastal sites). 31 Furthermore, Yates et al 4 reported that the site variable accounted for 17% of the variation in fur THg concentrations measured in 1447 bats (10 species) captured at 89 sites in northeastern USA.…”