Wendy K. Michaud

Mercury concentrations in landlocked Arctic char (Salvelinus alpinus) from the Canadian Arctic. Part II: Influence of lake biotic and abiotic characteristics on geographic trends in 27 populations

Among-lake variation in mercury (Hg) concentrations in landlocked Arctic char was examined in 27 char populations from remote lakes across the Canadian Arctic. A total of 520 landlocked Arctic char were collected from 27 lakes, as well as sediments and surface water from a subset of lakes in 1999, 2002, and 2005 to 2007. Size, length, age, and trophic position (delta(15)N) of individual char were determined and relationships with total Hg (THg) concentrations investigated, to identify a common covariate for adjustment using analysis of covariance (ANCOVA). A subset of 216 char from 24 populations was used for spatial comparison, after length-adjustment. The influence of trophic position and food web length and abiotic characteristics such as location, geomorphology, lake area, catchment area, catchment-to-lake area ratio of the lakes on adjusted THg concentrations in char muscle tissue were then evaluated. Arctic char from Amituk Lake (Cornwallis Island) had the highest Hg concentrations (1.31 microg/g wet wt), while Tessisoak Lake (Labrador, 0.07 microg/g wet wt) had the lowest. Concentrations of THg were positively correlated with size, delta(15)N, and age, respectively, in 88, 71, and 58% of 24 char populations. Length and delta(15)N were correlated in 67% of 24 char populations. Food chain length did not explain the differences in length-adjusted THg concentrations in char. No relationships between adjusted THg concentrations in char and latitude or longitude were found, however, THg concentrations in char showed a positive correlation with catchment-to-lake area ratio. Furthermore, we conclude that inputs from the surrounding environment may influence THg concentrations, and will ultimately affect THg concentrations in char as a result of predicted climate-driven changes that may occur in Arctic lake watersheds.

Changes in growth patterns of wild Arctic charr (Salvelinus alpinus (L.)) in response to fluctuating environmental conditions.

Several studies have revealed relationships between annual size-at-catch and various climatic factors for anadromous Arctic charr (Salvelinus alpinus) captured as part of the commercial fishery at Nain, Labrador (Nunatsiavut), Canada. Here, changes in growth patterns are examined among cohorts subject to differing lifetime temperature regimes, thereby considering the cumulative effects of past climate conditions instead of only annual fluctuations in temperature. An anomalous cold period, occurring in the Labrador region during the 1990s, was associated with a reduction in mean size-at-age for cohorts passing through this period. The physiological effect of temperature on growth was further exacerbated by a coincident change in the regional availability of preferred prey species. Mean sizes-at-age for cohorts experiencing a subsequent warm period, however, were not significantly larger than those observed for cohorts experiencing average cumulative lifetime temperatures. The latter result may be indicative of broader changes in ecosystem dynamics, exploitation rates and behaviour that coincided with the increase in temperature. The growth changes observed for the Nain Arctic charr stock complex indicate that climatic fluctuations can have both direct physiological effects on Arctic charr growth patterns as well as indirect effects through changes in ecosystem dynamics such as prey availability.