Environmental and food web determinants of Lake Trout mercury concentrations in Ontario Lakes

Prey composition and availability are considered a primary predictor of
Lake Trout (Salvelinus namaycush) mercury (Hg) concentrations. Evidence
from other freshwater fishes suggests that environmental and landscape
factors likely also contribute to fish Hg dynamics, yet comprehensive,
contemporary assessments for Lake Trout from boreal and north-temperate
lakes are lacking. Here, we reassess the importance of prey
characteristics using both previously published and contemporary data,
incorporating additional variables and model complexity to better
understand factors influencing Hg dynamics of Ontario Lake Trout. Our
analyses indicate that 1) Lake Trout Hg concentrations are primarily
associated with individual body size, 2) high dissolved organic carbon
(DOC) concentrations elevate Hg for fish of a given size, and 3) a coarse
categorization of food chain length, specifically the presence of Mysis
diluviana, informs Hg biomagnification slopes. The inclusion of DOC was
vital for assessing human consumption risk, as Lake Trout in high DOC
lakes were more likely to exceed Hg guidelines at sizes often harvested by
anglers. Drivers of Lake Trout Hg levels in boreal and north-temperate
lakes closely match those reported to affect other fishes in the region,
regardless of feeding, thermal, and habitat strategies.