Interactions of fish ecology, life history, food web structure, and mercury bioaccumulation in coastal Arctic lakes

I studied fish migration, fish ecology, food web structure, and mercury (Hg) accumulation in six lakes in the West Kitikmeot region of Nunavut, Canada, during 2006-2008. Three lakes contained partially anadromous populations of Arctic charr (Savelinus alpinus) whereas three lakes contained no Arctic charr. Through analyses of otolith microchemistry and stable carbon (C;delta13C), nitrogen (N;delta15N), and sulfur (5;delta34S) isotope ratios, I discovered that lake trout (Salvelinus namaycush) can adopt a partially anadromous life history strategy. Anadromous lake trout had significantly higher condition factors and C:N than resident lake trout, and anadromous lake trout began migrating to sea at a significantly older age (mean=13 years) than anadromous Arctic charr (mean=5 years). In contrast to results from freshwater habitats that support anadromous Pacific salmon species, stable isotope analysis did not indicate that significant amounts of marine-derived nutrients are imported into lakes via anadromous Arctic charr; delta15N and delta 13C of freshwater fish and invertebrate species did not differ between lakes with and without anadromous Arctic charr. However, resident lake trout were in significantly better condition and had significantly higher C:N in lakes where anadromous Arctic charr were present, whereas ninespine stickleback (Pungitius pungitius) had significantly lower condition in lakes where anadromous Arctic charr were present. Linear distance metrics applied to isotope data showed that food webs were more compact and isotopically redundant in lakes where Arctic charr were present and that lake trout occupied more isotope niche space and showed more inter-individual differences in feeding in lakes where Arctic charr were present. Fish mercury concentrations ([Hg]) depended on species, life history type, and whether anadromous Arctic charr were present. Arctic charr had significantly lower [Hg] than lake trout, anadromous lake trout had significantly lower [Hg] than resident lake trout, and resident lake trout had significantly lower [Hg] in lakes where anadromous Arctic charr were present. Differences in [Hg] were best explained by age-at-size, fish condition, C:N, and Hg biomagnification through food chains. Results of this study illustrate the ecological importance of anadromous Arctic charr in freshwater lakes, and have implications for fish conservation, stock management, and fish-derived Hg intake in humans.