No abstract

-Habitat and diet of Arctic charr Salvelinus alpinus (L.) were studied by monthly sampling from late autumn to early summer in Linnévatn, Svalbard (78°3¢N, 13°50¢E). This is the first year-round study of a population of charr in the High Arctic, with samples being taken every 5-7 weeks. The ice cover lasted for more than 9 months, from midOctober to late July, with the greatest thickness in mid-May. Although most charr occupied the littoral zone during winter, the highest densities in April and October were found in the deeper areas (20 m) of the lake. The fish fed at all times of the year, but the number of stomachs with food and the stomach-filling indices were lowest during the darkest part of the season. The diet of smaller charr (<15 cm) varied strongly with season, showing a dominance of zooplankton in late autumn and chironomids in winter (larvae) and summer (pupae). The food choice was in accordance with the density of food items available. Larger fish ( ‡15 cm) were mostly cannibalistic during the entire year.

A species-specific fractionation equation for Arctic charr (Salvelinus alpinus (L.)) was developed experimentally for use in ecological studies of temperature-driven phenologies for the species. Juvenile Arctic charr were reared in controlled conditions at different temperatures (2-14°C), with three replicates of each temperature. Otoliths from the fish and water samples from the chambers were analysed for oxygen isotope composition and used to estimate temperature-dependent fractionation equations relating the isotopic ratio to rearing temperature. A linear and a second order polynomial relationship were estimated and validated using comparable Arctic charr data from another study. Temperatures predicted using the polynomial equation were not significantly different from recorded experimental temperatures, whereas with the linear equation there were significant differences between the predicted and measured temperatures. The polynomial equation also showed the least bias as measured by mean predictive error. Statistical comparisons of the polynomial fractionation equation to a similarly estimated equation for brook charr (Salvelinus fontinalis (Mitchill)) indicated significant differences. Results imply the need for species-specific fractionation equations, even for closely related fish. Results further suggest the polynomial form of the fractionation equation will facilitate more accurate characterisation of water temperatures suitable for use in ecological studies of temperature-driven phenologies of Arctic charr.

Human activities have the potential to accelerate population-level decline by contributing to climate warming and decreasing the capacity of species to survive warming temperatures. Here we build a predictive model to test interactions between river warming and catch-and-release mortality in recreational fisheries for Atlantic salmon (Salmo salar L.) by compiling and analyzing published data. We then test if warming has occurred in rivers where angling occurs, and if angling opportunities have been restricted through increased river closures due to high water temperatures. We find that catch and release mortalities are low (< 0.05) at cool river temperatures (< 12°C). At river temperatures often leading to fishery closures (between 18 and 20°C), mortalities range from 0.07 to 0.33 (mean = 0.16). River temperatures on the east and southeast coasts of Newfoundland have warmed leading to an increase in fishery closures in recent years. By contrast, river temperatures in southern Labrador have warmed slightly, with only one documented river closure. Accordingly, increasing temperatures will increase the frequency of river closures and likely result in higher mortality in caught and released Atlantic salmon in rivers that remain open to catch and release angling at warm water temperatures.