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.

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.

Scale patterns, maturational status and otolith microchemistry (strontium to calcium ratios) were analysed in sympatric anadromous and non-anadromous rainbow trout Oncorhynchus mykiss in the Santa Cruz River (Patagonia, Argentina) to investigate the life-history differences of anadromous and non-anadromous lifestyles and the association between maternal origin and progeny life history. The analyses revealed that both forms can give rise to one another, indicating a single population with alternative phenotypes. Anadromous fish smolted at ages 2 and 3 years, matured after 1 to 2 years in the ocean, and survived up to 11 years, spawning up to eight times. Non-anadromous fish survived up to 6 years, spawning up to three times. The extended reproductive life span associated with anadromy in this river suggests that increased energetic and physiological demands associated with ocean migration may not necessarily result in reduced postspawning survival, as has been suggested for salmonids in general. Alternatively, reduction in parity may be regarded as the evolutionary outcome of reproductive traits resulting from the adoption of anadromy (i.e. augmented reproductive investment) coupled with longrange migrations to and from the ocean. The life-history patterns of Santa Cruz River rainbow trout provide a natural experiment for investigating the evolutionary transition and maintenance of anadromy and non-anadromy within salmonid populations.

Scanning proton microprobe analysis was used to determine the distribution of strontium (Sr) in otoliths from arctic charr (Salvelinus alpinus) of known non-anadromous, known anadromous, and unknown life histories. Strontium concentration patterns in otoliths of known non-anadromous charr were low and relatively flat (with little variation) from the core area to the outermost edge of the otolith, while patterns for known anadromous charr were characterized by a similar low, flat region for the first several years of life, followed by marked oscillatory increases and decreases in Sr content for the duration of the fish's life. Small and large forms of Lake Hazen charr of unknown life histories exhibited Sr profiles that were similar to those of the known non-anadromous charr, which strongly suggests that Lake Hazen charr are non-anadromous. These results indicate that Lake Hazen is a "closed" system with energy cycling primarily within the system; this conclusion suggests that a conservative approach would be appropriate for the management of the Lake Hazen charr population.

Eight sexually mature sockeye (Oncorhynchus nerka) and one sexually mature pink salmon (O. gorbuscha) were captured in the subsistence fishery in the Sachs River estuary at Sachs Harbour, Banks Island, Northwest Territories (NT) in August 1993. We also report a first record for coho salmon (O. kisutch) in Great Bear Lake, NT. These capture locations are well outside the known distributions for the species. A pink salmon captured in the West Channel, Mackenzie River near Aklavik, NT, and a chum salmon (O. keta) from Cache Creek, NT, also represent new capture locations within the distribution of the species.

There is growing recognition of the global importance of preserving biodiversity. While many organisms show immense variation in intraspecific biodiversity, for example in life history variation and migratory strategies among conspecific populations, accurate descriptions of such variation are lacking for the majority of contemporary species. One such example is the broad whitefish Coregonus nasus of the lower Mackenzie River system in Canada's Northwest Territories, where anadromous, lacustrine, and putative riverine populations are thought to exist. In this study we resolve migratory variation exhibited by lower Mackenzie River broad whitefish by employing otolith microchemistry and find that (1) anadromous, lacustrine, and riverine populations exist in this system, (2) a high degree of variability exists within anadromous broad whitefish (e.g., varying degrees of marine and estuarine use), and (3) lacustrine populations are not composed solely of resident fish as anadromous broad whitefish occasionally migrate to, and stay in, lacustrine habitat. Overall, our results are consistent with the suggestion that there may be a higher level of migratory complexity in this system than previously reported and these results will be important in guiding the conservation of intraspecific biodiversity in Mackenzie River system broad whitefish.