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Meristic characters are often used to differentiate between closely related forms, morphs, and species of fishes, and lend insight into ecology and post‐glacial recolonization in taxa with complicated or contentious phylogenies, including the genus Salvelinus. Previous studies of meristics in Salvelinus have focused mostly on individual populations. We collated data from 456 populations/systems across the North American and Russian Arctic and sub‐Arctic, and found that counts of pyloric caeca and gill rakers differed consistently between fish visually and/or genetically identified as Arctic char and Dolly Varden across their distributional ranges. [ABSTRACT FROM AUTHOR]

Native lake trout (Salvelinus namaycush) and introduced Chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), steelhead (Oncorhynchus mykiss), and brown trout (Salmo trutta) are major predators in Lake Michigan's complex ecosystem and collectively support a valuable recreational fishery, but declines in their primary prey, alewife (Alosa pseudoharengus), have raised ecological and management concerns about competition and prey allocation. We applied niche overlap analysis to evaluate competition among salmonine predators during rapid forage base change in Lake Michigan. [[delta].sup.13]C and [[delta].sup.15]N stable isotope ratios indicated that lake trout had a unique trophic niche from inclusion of offshore and benthic prey, with Si les truites grises (Salvelinus namaycush) indigenes et les saumons chinooks (Oncorhynchus tshawytscha), les saumons cohos (Oncorhynchus kisutch), les truites arc-en-ciel (Oncorhynchus mykiss) et les truites brunes (Salmo trutta) introduits sont d'importants predateurs dans l'ecosysteme complexe du lac Michigan et soutiennent collectivement une peche sportive de grande valeur, des declins de leur principale proie, le gaspareau (Alosa pseudoharengus), ont toutefois suscite des inquietudes relatives a leur ecologie et leur gestion touchant a la concurrence et la repartition des proies. Nous avons utilise l'analyse du chevauchement des niches pour evaluer la concurrence entre des predateurs salmonines durant des changements rapides des bases d'alimentation dans le lac Michigan. Les rapports d'isotopes stables [[delta].sup.13]C et [[delta].sup.15]N indiquent que la truite grise occupe une niche trophique distincte decoulant de l'inclusion de proies benthiques et du large, dont, Introduction Niche theory has evolved since it was first described by Grinnell (1917), and defining an organism's niche can be challenging for ecologists due to multiple definitions that can include [...]

We investigated the spatial overlap, diet, isotopic niche, and growth of juvenile lean and siscowet lake charr (Salvelinus namaycush) in Lake Superior to address concerns of potential competition with implications to the study of resource polymorphism. Catch data revealed the greatest levels of sympatry in waters from 40 to 60 m. Juvenile lean and siscowet diet changed ontogenetically with Mysis being the dominant prey item for the smallest lake charr but differentiating with onset of piscivory. As ecotypes increased in size, lean diets became dominated by pelagic prey, whereas siscowets had equal proportions of benthic and pelagic prey. Isotopic niche overlap declined between ecotypes coincident with siscowet lake charr shifting to deeper habitats around 400 mm. Lean and siscowet exhibited different growth trajectories. However, length at age-4 declined in parallel for both ecotypes with no trend in condition suggesting that lake charr growth is sensitive to prey biomass and unlikely related to competition. Our findings indicate minimal evidence of competition and support the concept that multiple sympatric ecotypes of lake charr in Lake Superior are maintained by resource polymorphism. [ABSTRACT FROM AUTHOR]

In occupancy models, imperfect detectability of animals is usually corrected for by using temporally repeated surveys to estimate probability of detection. Substituting spatial replicates for temporal replicates could be an advantageous sampling strategy in remote Arctic regions, but may lead to serious violations of model assumptions. Using a case study of site occupancy of adfluvial young-of-year Arctic grayling (Thymallus arcticus) in Barrenland tundra streams, we assessed the reliability and efficiency of alternative sampling strategies: (i) randomly distributed versus sequential adjacent spatial replicates; (ii) visual versus electrofishing surveys; and (iii) spatial versus temporal replicates. Sequential, adjacent spatial replicates produced spatially autocorrelated data. Autocorrelation was relieved using randomly distributed spatial replicates, but using these randomly distributed spatial replicates introduced significant error into estimates of the probability of occupancy in streams. Models designed for spatially autocorrelated data could minimize this bias. Visual and electrofishing surveys produced comparable probabilities of detection. Spatially replicated surveys performed better than temporal replicates. The easiest and relatively most cost-effective sampling methods performed as well as, or better than, the more established, expensive, and logistically difficult alternatives for occupancy estimation. Dans les modeles d'occupation, une correction pour tenir compte du caractere imparfait de la detectabilite des animaux est habituellement faite en utilisant des recensements repetes dans le temps pour estimer la probabilite de detection. Si le remplacement des recensements repetes dans le temps par des recensements repetes dans l'espace pourrait constituer une strategie d'echantillonnage avantageuse dans les regions eloignees de l'Arctique, il pourrait aussi mener a des violations graves des hypotheses qui sous-tendent les modeles. En utilisant une etude de cas d'occupation de sites par des ombres arctiques adfluviaux jeunes de l'annee (Thymallus arcticus) dans des cours d'eau de la toundra canadienne, nous avons evalue la fiabilite et l'efficience de differentes strategies d'echantillonnage, a savoir (i) des recensements aleatoirement repetes dans l'espace par rapport a des recensements adjacents et sequentiels dans l'espace, (ii) des recensements visuels par rapport a des recensements par peche electrique et (iii) des recensements repetes dans l'espace par rapport a des recensements repetes dans le temps. Les recensements adjacents et sequentiels dans l'espace produisaient des donnees spatialement autocorrelees. Cette autocorrelation a ete reduite en utilisant des recensements aleatoirement repetes dans l'espace, mais l'utilisation de ces derniers introduisait une erreur significative dans les estimations de la probabilite d'occupation dans les cours d'eau. Les modeles concus pour des donnees presentant une autocorrelation spatiale peuvent minimiser ce biais. Les recensements visuels et par peche electrique ont produit des probabilites de detection semblables. Les recensements repetes dans l'espace ont donne de meilleurs resultats que les recensements repetes dans le temps. Les methodes d'echantillonnage les plus faciles et relativement moins couteuses ont donne des resultats aussi bons, sinon meilleurs, que les methodes mieux etablies, plus couteuses et plus difficiles autiliser pour l'estimation de l'occupation. [Traduit par la Redaction], Introduction Freshwater ecosystems in the Arctic are experiencing a rapid change in climate and increasing pressure from ever-growing industrial development. The impacts of anthropogenic stressors on hydrology, water temperature, primary [...]

The importance of marine prey sources for partially anadromous fishes has received little study and is complicated by considerable plasticity in life history. We determined proportional contributions of marine, freshwater benthic, and freshwater pelagic prey to anadromous and resident Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush) from several partially anadromous populations in the Canadian Arctic. Bayesian mixing models (MixSIR) applied to δ[sup.14]S and δ[sup.13]C ratios in lake-specific models indicated that marine prey accounted for 90%-91% of anadromous Arctic char diet and 60%-66% of anadromous lake trout diet. When these estimates were combined with proportion of anadromous individuals in partially anadromous populations, marine food sources accounted for 31%-44% of Arctic char population productivity and 16%-26% of lake trout population productivity. Although future research is needed to refine and quantify variability around these estimates, our results will allow better predictions of the effects of anthropogenic stressors on partially anadromous fishes. On a peu etudie l'importance des sources de proies marines pour les poissons partiellement anadromes et cette etude est compliquee par la tres grande plasticite des cycles biologiques. Nous avons mesure les contributions proportionnelles des proies marines, benthiques d'eau douce et pelagiques d'eau douce chez des ombles chevaliers (Salvelinus alpinus)et des touladis (Salvelinus namaycush) anadromes et sedentaires dans plusieurs populations partiellement anadromes dans l'Arctique canadien. Des modeles de melange bayesiens (MixSIR) utilises sur des rapports δ[sup.34]S et δ[sup.13]C dans des modeles specifiques aux lacs indiquent que les proies marines representent 90-91 % du regime alimentaire des ombles chevaliers anadromes et 60-65 % du regime alimentaire des touladis anadromes. Une fois ces estimations combinees a la proportion d'individus anadromes dans les populations partiellement anadromes, les sources alimentaires marines expliquent 31-44 % de la productivite de la population d'ombles chevaliers et 16-26 % de la productivite de la population de touladis. Bien qu' il faille des recherches supplementaires pour preciser et mesurer la variabilite de ces estimations, nos resultats permettent de meilleures predictions des effets des facteurs anthropiques de stress sur les poissons partiellement anadromes. [Traduit par la Redaction], Introduction Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush) are of economic, cultural, and subsistence importance in the Canadian Arctic, and their presence in Arctic lakes affects food web [...]

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 δ[.sup.15]N (mean = 16.4‰), δ[.sup.13]C (mean = -22.3‰), and δ[.sup.34]S (mean = 13.43‰) isotope ratios than resident lake trout (means = 12.84‰, -26.21‰, and 1.93‰ for δ[.sup.15]N, δ[.sup.13]C, and δ[.sup.34]S, 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. Resume: Dans la famille des Salmonidae, ce sont les touladis (Salvelinus namaycush) qui sont consideres les moins tolerants a l'eau salee. On signale neanmoins de temps a autre la presence de touladis dans les habitats cotiers et saumatres de l'Arctique canadien. Des analyses microchimiques des otolithes faites sur des touladis et des ombles chevaliers (Salvelinus alpinus) de quatre lacs arctiques dans la region du Kitikmeot occidental au Nunavut, Canada, montrent que 37 de 135 (27 %) touladis avaient fait des migrations annuelles en mer. Les touladis anadromes sont en significativement meilleure condition (K = 1,17) et possedent un rapport C:N (3,71) relativement plus eleve que les touladis residants (K = 1,05 et C:N = 3,34). Les touladis anadromes ont aussi des rapports d'isotopes δ[.sup.15]N (moyenne = 16,4‰), δ[.sup.13]C (moyenne = -22,3 ‰) et δ[.sup.34]S (moyenne = 13,43 ‰) plus eleves que ceux des touladis residants (moyennes de 12,84 [per thousand], -26,21 ‰ et 1,93 ‰ pour respectivement δ[.sup.15]N, δ[.sup.13]C et δ[.sup.34]S); les resultats sont semblables chez les ombles chevaliers et concordent avec ceux des etudes anterieures. L'age moyen de la premiere migration chez le touladi est de 13 ans, ce qui est significativement plus tard que chez l'omble chevalier (5 ans). Cela pourrait refleter une tolerance a la salinite reliee a la taille chez le touladi, mais il faut des recherches supplementaires sur le sujet. Nos resultats representent les premieres donnees scientifiques detaillees sur l'anadromie chez le touladi. [Traduit par la Redaction], Introduction Although lake trout (Salvelinus namaycush) are commonly thought to be restricted to freshwater habitats, there are sporadic records of this species inhabiting brackish, coastal environments in the Canadian Arctic [...]

Globally, relationships between avian richness and elevation in mountain ecosystems typically reflect one of four well‐documented patterns, but the mechanisms responsible for these patterns are poorly understood. We investigated which pattern best described bird species richness in peatlands of the Upper Bow Basin of the Canadian Rocky Mountains (1300–2000 m a.s.l.) and used a model competition framework to investigate possible mechanisms. Avian richness displayed a plateauing (cubic) relationship in response to increasing elevation (AICc weight = 0.48). Log richness was significantly positively related to log peatland area (R2 = 0.42, p = 0.001); however, and once we accounted for the richness–area relationship (area was not related to elevation (R2 = 0.13, p = 0.083)), the richness–elevation relationship was best described by a negative linear model rather than a cubic model (AICc weight = 0.69, R2 = 0.39). Consequently, we reject the neutral model of the mid‐domain effect and conclude that peatland area and one or more environmental filters are simultaneously driving relationships between avian richness and elevation in Rocky Mountain peatlands. Multicausality likely explains why researchers in different geographies observe inconsistent patterns between richness and elevation: drivers and interactions among drivers may vary spatially. Importantly, Natural Subregion was a stronger predictor of avian species richness than elevation per se (AICc weight = 0.96), suggesting that the responsible environmental filter(s) is relatively homogenous within ecological land classes (e.g. primary productivity) rather than directly variable with elevation (e.g. temperature). The results also lend insight into priorities for future research on richness–elevation patterns in mountain birds. [ABSTRACT FROM AUTHOR]

To better understand the risks and benefits of eating wild-harvested fish from the Northwest Territories, Canada, levels of total mercury (HgT) and selenium (Se) and composition of omega-3 fatty acid (n-3 FA) were measured in muscle tissue of fish harvested from lakes in the Dehcho Region, Northwest Territories, Canada. Average HgT levels ranged from 0.057 mg/kg (cisco) to 0.551 mg/kg (northern pike), while averagen-3 FA concentrations ranged from 101 mg/100 g (burbot) to 1,689 mg/100 g (lake trout). In contrast to HgT andn-3 FA, mean Se concentrations were relatively similar among species. Consequently, species such as lake whitefish, cisco, and longnose sucker displayed the highest nutrient levels relative to HgT content. Levels of HgT tended to increase with fish size, while Se andn-3 FA levels were typically not associated with fork length or fish weight. Interestingly, HgT concentration was occasionally inversely related to tissue nutrient content. Significant negative correlations were observed between Hg andn-3 FA for lake trout, northern pike, and walleye. There were also significant negative correlations between Hg and Se noted for lake whitefish, cisco, and northern pike. Samples with the highest nutritional content displayed, on occasion, lower levels of HgT. This study provides valuable information for the design of probabilistic models capable of refining public health messaging related to minimizing Hg risks and maximizing nutrient levels in wild-harvested fish in the Canadian subarctic. [ABSTRACT FROM PUBLISHER]