Assessing reasons for changes in the condition of Deception Bay Arctic charr (Salvelinus alpinus)

Abstract

The Raglan Mine sport fishing program has collected biological fish data in Deception Bay, Nunavik, Québec, Canada since 1998 in collaboration with local committees, small scale sampling programs, and government agencies and since 2004 there has been a documented and continued decline in the somatic condition of anadromous Deception Bay Arctic charr. Anadromous Arctic charr in Deception Bay support subsistence, recreational, and commercial fisheries, but research focused on this population of Arctic charr is limited, dated, and summer specific. In an effort to address the concerns of neighbouring communities regarding the observed declines in the somatic condition and to improve the overall available data on anadromous Nunavik Arctic charr populations, this research investigated seasonal variation in fish condition measures (lipid analysis and bomb calorimetry) and contaminant levels (arsenic, cadmium, chromium, copper, mercury, nickel, lead, and zinc) and their potential linkages with biological variables and indicators of feeding behaviour in Arctic charr returning from the marine environment (Deception Bay – summer 2016) and during the post-winter season (Deception River headwater lakes, Duquet and Françoys-Malherbe – spring 2017).

Biological information (fork-length, whole-weight, age, somatic condition), stable isotope values (δ13C, % carbon, δ15N, and % nitrogen), and dorsal muscle % lipid values, caloric densities, and total mercury concentrations were assessed to determine the seasonal variability of these parameters in this population of anadromous Arctic charr. Significant reductions in somatic condition and % nitrogen, consistent with prolonged periods of non-feeding, existed for post-winter captured Arctic charr, but % lipid and caloric values were significantly greater in dorsal muscle tissue of fish collected during this season. Significant correlations between data from these analyses and fork-length, whole-weight, age, somatic condition, δ13C, % carbon, δ15N, and % nitrogen were seasonally dependent and only existed between some of the tested variables. Total mercury concentrations also varied seasonally, with concentrations being significantly greater in the tissue collected from summer returning marine migrants. Similar to observations with lipid and caloric values, significant relationships were seasonally dependent and only existed between total mercury concentrations and some, but not all, of the tested variables. Total mercury concentration data also had limited relationships with fish condition measures, only significantly declining with increasing % lipid values in Arctic charr sampled in the marine environment. Biological descriptors and stable isotope values, in addition to season, were incorporated into multi-predictor variable models that better explained variations in the data than individual parameters. Season, condition, and stable isotope values (% carbon and % nitrogen) were the best indicators of % lipid content and caloric densities, while total mercury concentration data were best supported by whole-weight measurements, somatic condition, and δ13C. Seasonal variation in fish condition measures and results from total mercury analysis may be indicative of a condition selective mortality effect on this population, while winter diet subsidization is less plausible due to the observed absence of short term feeding and depletion of % nitrogen values. Future research must consider the implications of the phenomenon on mature fish, particularly in extreme environments, such as the Arctic.

Dorsal muscle and liver concentrations of arsenic, cadmium, chromium, copper, nickel, lead, and zinc were also quantified to examine possible organotropism, seasonal variation, and relationships with biological variables (fork-length, age, and condition) and stable isotopes (carbon and nitrogen). Metal organotropism favouring elevation in liver tissues 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 that better explained variations in the data. Variation in trace metal concentration data were often best supported when season, somatic condition, and trophic descriptors were included and these variables dominated as the parameters of greatest relative importance across all considered metals and tissue types. Fork-length also appeared as a variable of high relative importance for essential metals, while age and δ15N were of greater relative importance to non-essential metals. These findings suggest that seasonally linked processes have the greatest influence on trace metal concentrations in anadromous Arctic charr and future metals related research on Arctic charr and other northern fish species should further consider these variables when evaluating elemental accumulation.