Trophic structure and mercury transfer in the subarctic fish community of Great Slave Lake, Northwest Territories, Canada

In recent decades, mercury concentrations have increased in fish of Great
Slave Lake (GSL), a subarctic great lake in northern Canada with important
recreational, subsistence, and commercial fisheries. This study
characterized habitat use and trophic position of common fish species in
GSL near the City of Yellowknife (Northwest Territories, Canada), measured
mercury concentrations in water and in taxa from lower trophic levels of
the food web, and examined trophic and biological influences on mercury
concentrations within and among fish species. Northern pike (Exos lucius)
and lake whitefish (Coregonus clupeformis) fed predominantly nearshore,
cisco (Coregonus artedi) and longnose sucker (Catostomus catostomus) fed
predominantly offshore, and burbot (Lota lota) fed roughly equally in both
habitats. Habitat-specific feeding did not influence mercury
bioaccumulation in fish, in contrast with published studies of smaller
lakes. Water concentrations of total mercury and methylmercury were low
and showed little spatial variation among sites or depths. Zooplankton
(>200 µm) had similarly low methylmercury concentrations to
littoral and profundal amphipods, suggesting little habitat-variation of
mercury exposure near the base of the food web. Age, size, and trophic
position were significant explanatory variables for muscle total mercury
concentrations within populations of fish species. Among fish species,
size and trophic position explained 80% of the variation in muscle total
mercury concentrations. This study generated the most comprehensive
dataset to date on mercury bioaccumulation in the food web of GSL, which
will serve as a baseline for future studies of this great lake.