Seasonal variation of total mercury and condition indices of Arctic charr (Salvelinus alpinus) in Northern Quebec, Canada

Thewinter ecology of anadromous Arctic charr, an important fish species for Indigenous populations, has remained poorly detailed in the literature beyond descriptions of seasonal fasting and resulting declines in condition. However, prolonged periods of reduced feeding can have significant consequences for other variables, such as tissue contaminant levels. To more thoroughly detail seasonal changes, biological information (fork length, total weight, age, sex, somatic condition), stable isotopes (delta 13C, % carbon, delta 15N, % nitrogen), dorsal muscle % lipid, caloric densities, and totalmercury (THg) concentrationswere assessed in anadromous Arctic charr collected fromDeception Bay, Canada, during the summer and over-wintering periods. Significant reductions in somatic condition, total weight, and % nitrogen, consistent with prolonged periods of fasting, were found for post-winter captured Arctic charr, but % lipid and caloric densities were significantly higher in these fish. THg also varied seasonally and was significantly higher in summer collected tissue. When tested individually via linear regression, significant relationshipswere seasonally dependent, but limited in number. All previously mentioned parameterswere then incorporated intomulti-variablemodelswhich better explained variations in the data. While therewas no clear bestmodel for explaining the % lipid values, caloric densities, and THg, season, condition, and stable isotope values (% carbon and % nitrogen) were the best indicators of % lipid content and caloric densities. THg concentrations were best explained by total weight, somatic condition, and delta 13C. Seasonal variation in fish conditionmeasures and THgmay be indicative of condition selectivemortality that yields apparent improvement through the disproportionate removal of poorer conditioned fish fromthe population during the over-wintering period. This hypothesiswas further supported by mortality estimates and the results of the multi-predictor variable models. Collectively, this research highlights the importance of understanding seasonal dynamics for anadromous Arctic charr populations. (c) 2020 Published by Elsevier B.V.