In the family Salmonidae, lake trout ( Salvelinus namaycush ) are considered the least tolerant of salt water. There are, however, sporadic reports of lake trout in coastal, brackish habitats in the Canadian Arctic. Otolith microchemistry analyses conducted on lake trout and Arctic char ( Salvelinus alpinus ) from four Arctic lakes in the West Kitikmeot region of Nunavut, Canada, revealed that 37 of 135 (27%) lake trout made annual marine migrations. Anadromous lake trout were in significantly better condition (K = 1.17) and had significantly higher C:N ratios (3.71) than resident lake trout (K = 1.05 and C:N = 3.34). Anadromous lake trout also had significantly higher δ15N (mean = 16.4‰), δ13C (mean = –22.3‰), and δ34S (mean = 13.43‰) isotope ratios than resident lake trout (means = 12.84‰, –26.21‰, and 1.93‰ for δ15N, δ13C, and δ34S, respectively); results were similar for Arctic char and agree with results from previous studies. Mean age of first migration for lake trout was 13 years, which was significantly older than that for Arctic char (5 years). This could be a reflection of size-dependent salinity tolerance in lake trout, but further research is required. These are the first detailed scientific data documenting anadromy in lake trout.

Stable isotopes of carbon and nitrogen were used to examine differences in the feeding ecology of sympatric morphotypes of Arctic charr Salvelinus alpinus from Lake Hazen, Ellesmere Island, in the Canadian High Arctic. Large and small morphotypes possessed significantly different carbon and nitrogen signatures with large-form Arctic charr being more depleted in 13 C and more enriched in 15 N than the small-form. Isotope and stomach content analyses yielded consistent results and indicated short-and long-term reliance on fish as a food for large Arctic charr. Large-form individuals predate on juveniles but do not predate on small-form individuals d250 mm. The observed cannibalism by large-form individuals, therefore, does not act to maintain the bimodal length-frequency distribution in Lake Hazen. Bimodality is argued to arise for ecological reasons connected with differing habitat use by the morphotypes and the associated differences in resource consumption opportunities. 2002 The Fisheries Society of the British Isles

Because trace elements from the environment are incorporated into the otoliths of fish as they grow, otolith microchemistry can be used to reconstruct key aspects of their environmental history, such as migratory patterns. We used scanning proton microprobe analysis on otoliths of inconnu Stenodus leucichthys from the Mackenzie River system (Northwest Territories, Canada) to determine whether patterns of strontium (Sr) distribution supported the hypothesis that some populations are anadromous while others remain in a low‐Sr freshwater environment. The otoliths of inconnu from the Slave River had low, flat Sr profiles, indicating that these fish spent their entire lives within a freshwater environment. In contrast, while the otoliths of inconnu from the Arctic Red River varied substantially, they generally had low, flat profiles near the core followed by oscillating patterns of high and low Sr through to the outer edge of the otolith. These latter profiles indicate that these fish spent their first 1–2 years in a freshwater environment and then moved annually into a higher‐Sr environment, such as the Mackenzie estuary or Beaufort Sea. A subset of fish from the Arctic Red River, primarily males, revealed smaller annular maxima or ranges of Sr concentrations and were considered partially anadromous. Because the salinity of the environment consistently correlates strongly with Sr levels in otoliths, otolith Sr can provide a reliable tool for examining the life history and migratory patterns of diadromous species that are otherwise difficult to study directly.