A seasonal comparison of trace metal concentrations in the tissues of Arctic charr (Salvelinus alpinus) in Northern Québec, Canada

Ecotoxicological research detailing trace metal contamination and seasonal variation in the tissues of northern fishes such as Arctic charr (Salvelinus alpinus) has been poorly represented in the literature beyond examination of mercury. In an effort to address this, anadromous Arctic charr were collected from the Deception River watershed in the late summer and post-winter season, before quantifying seasonal and organotropic variations in dorsal muscle and liver concentrations of arsenic, cadmium, chromium, copper, nickel, lead, and zinc. Potential linkages with biological variables (fork length, age, and somatic condition) and indicators of feeding behavior (δ¹³C and δ¹⁵N) were also assessed. Trace metal organotropism favouring elevation in liver tissue concentrations was exhibited by cadmium, copper, nickel and zinc, while arsenic, chromium and lead exhibited no significant organotropic variation. Seasonal differences in concentrations were metal and tissue dependent, but generally increased in tissues collected from post-winter sampled Arctic charr. Significant correlations with biological and trophic descriptors were also determined to be element and tissue dependent. These parameters, in addition to season, were incorporated into multi-predictor variable models, where variations in trace metal concentration data were often best explained when season, somatic condition, and trophic descriptors were included. These variables were also of greatest relative importance across all considered trace metals and tissue types. These findings suggest that seasonally linked processes have the greatest influence on trace metal concentrations in anadromous Arctic charr. Future metal-related research on Arctic charr and other northern fish species should further consider these variables when evaluating elemental accumulation.

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

The winter 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 (δ13C, % carbon, δ15N, % nitrogen), dorsal muscle % lipid, caloric densities, and total mercury (THg) concentrations were assessed in anadromous Arctic charr collected from Deception 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 relationships were seasonally dependent, but limited in number. All previously mentioned parameters were then incorporated into multi-variable models which better explained variations in the data. While there was no clear best model 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 δ13C. Seasonal variation in fish condition measures and THg may be indicative of condition selective mortality that yields apparent improvement through the disproportionate removal of poorer conditioned fish from the population during the over-wintering period. This hypothesis was 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.