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Arctic fishes are threatened by climatic change and other anthropogenic stressors, yet information on how such changes impact survival remains scarce. Acoustic telemetry has become valuable for studying aspects of fish ecology, including survival, which is invaluable in understanding potential responses to changing conditions. In Cambridge Bay, NU, we have been using acoustic telemetry to study movements and habitat use of the culturally and commercially important Arctic char (Salvelinus alpinus). Here, we combine acoustic telemetry data and Bayesian multistate mark–recapture models to study the survival of Arctic char from 2014 to 2018 in the region in freshwater and marine/estuarine habitats. We found that survival probabilities were high (>0.87) and models considering two environments (freshwater and marine) perform better than those considering three (including estuarine habitats). Furthermore, the survival in fresh water was higher than survival in marine/estuary environments. Overall, the results of this study further our understanding of important demographic parameters (i.e., survival) for Arctic char in the region, which will be useful in refining fishery management plans for the largest commercial fishery for this species in Canada. [ABSTRACT FROM AUTHOR]

Arctic Char, Salvelinus alpinus, are frequently exploited in the Halokvik and Jayko rivers by Cambridge Bay fishers for subsistence and commercial purposes. Commercial fisheries for anadromous Arctic Char in the Halokvik River date back to 1968 and at the Jayko River the commercial fishery began in 1975; both have been subjected to periodic closures throughout their history. Harvest data are available for both systems and each has a long-time series of fishery-dependent data. Fishery-independent data are limited for both waterbodies. Through collaboration with the Ekaluktutiak Hunters and Trappers Organization (EHTO), Fisheries and Oceans Canada (DFO) developed the Cambridge Bay Arctic Char Integrated Fisheries Management Plan (IFMP) to promote a common understanding of the "basic rule" for the sustainable management of arctic fisheries. To assess the sustainability of these stocks and to further our understanding of commercial harvest on stock persistence, we applied depletionbased stock reduction analysis (DB-SRA) and other data limited models to assess Arctic Char status and formulate sustainable fisheries management options. Our data indicate that commercial fishery harvests in both rivers underwent significant inter-annual variation. Growth in standard length and round weight of anadromous Arctic Char differed with year, river and sex. Male fish had 16% higher L8 and 18% lower k values than females in the Halokvik River while male char had 4% higher L8 and 9% higher k at the Jayko River. In terms of empirical relationships between natural mortality and somatic growth parameters, M was estimated to be 0.1485 ± 0.1272 per year and 0.1758 ± 0.0372 per year at the Halokvik and Jayko rivers, respectively. Using the DB-SRA model, the mean and standard error values of virgin biomass (K) were estimated to be 104.99 ± 0.55 t and 167.15 ± 0.58 t in the Halokvik and Jayko rivers, respectively. Arctic Char in the Halokvik River appeared healthy before 1988 and the population appears to have been overfished since then. Fishing pressure was acceptable until 2004 and the fisheries showed a five-year period of overexploitation during 2005-2010. Currently, the population is still in the overfished state. In the Jayko River, a healthy state was sustained until 1992. Since then, the population has been in an overfished state as F increased. In particular, since 2012, the population has been overfished as the fishery is in a state of moderate overexploitation. Both fisheries have experienced overfishing as determined by the assessment. [ABSTRACT FROM AUTHOR]

Anadromy was documented in 16 lake trout, Salvelinus namaycush, from Canada's central Arctic using capture data and otolith microchemistry. For the first time, estuarine/marine habitat use was described for five individuals using acoustic telemetry. Age‐at‐first‐migration to sea was variable (10–39 years) among individuals and most S. namaycush undertook multiple anadromous migrations within their lifetime. Telemetry data suggested that S. namaycush do not travel far into marine habitats and prefer surface waters (<2 m). These results further our collective understanding of the marine ecology of Arctic S. namaycush. [ABSTRACT FROM AUTHOR]

Partial anadromy is common within salmonid populations, where resident and anadromous individuals interbreed and overlap in habitat use during portions of life. Deviation to this definition occurs within the Husky Lakes drainage basin (HLDB), Northwest Territories, where freshwater resident, semi-anadromous, and brackish-water resident lake trout ( Salvelinus namaycush) life history types are documented. In this study, microsatellite DNA variation was assayed to evaluate genetic structuring among life history types from the HLDB and adjacent lower Mackenzie River system. Significant differentiation was resolved among most locations and life histories (global FST = 0.192). Brackish-water residents were differentiated from all locations and life histories, including sympatric semi-anadromous individuals, providing evidence for genetically fixed strategies. Also, this provides the first evidence of breeding partial migration in salmonids using brackish-water environments, where brackish-water residents and semi-anadromous migrants interact during the nonbreeding season, but the latter migrate elsewhere to spawn. Alternatively, the lack of genetic differentiation between semi-anadromous and Sitidgi Lake residents suggests conditional mating tactics may also influence partial anadromy. This work provides novel insights into partial anadromy in Arctic salmonids and expands our knowledge of biodiversity in this region. [ABSTRACT FROM AUTHOR]

Migration is a ubiquitous life history trait with profound evolutionary and ecological consequences. Recent developments in telemetry and genomics, when combined, can bring significant insights on the migratory ecology of nonmodel organisms in the wild. Here, we used this integrative approach to document dispersal, gene flow and potential for local adaptation in anadromous Arctic Char from six rivers in the Canadian Arctic. Acoustic telemetry data from 124 tracked individuals indicated asymmetric dispersal, with a large proportion of fish (72%) tagged in three different rivers migrating up the same short river in the fall. Population genomics data from 6,136 SNP markers revealed weak, albeit significant, population differentiation (average pairwise FST = 0.011) and asymmetric dispersal was also revealed by population assignments. Approximate Bayesian computation simulations suggested the presence of asymmetric gene flow, although in the opposite direction to that observed from the telemetry data, suggesting that dispersal does not necessarily lead to gene flow. These observations suggested that Arctic Char home to their natal river to spawn, but may overwinter in rivers with the shortest migratory route to minimize the costs of migration in nonbreeding years. Genome scans and genetic-environment associations identified 90 outlier markers putatively under selection, 23 of which were in or near a gene. Of these, at least four were involved in muscle and cardiac function, consistent with the hypothesis that migratory harshness could drive local adaptation. Our study illustrates the power of integrating genomics and telemetry to study migrations in nonmodel organisms in logistically challenging environments such as the Arctic. [ABSTRACT FROM AUTHOR]

We used an array of fixed acoustic receivers ( N = 42) to track the summer marine movements of 121 anadromous Arctic char ( Salvelinus alpinus) equipped with acoustic transmitters at three locations in the Cambridge Bay region, where commercial and subsistence fisheries target the species. The timing of transitions between salt and fresh water was influenced by the putative river of origin of tagged individuals, but not by their size or sex. Females, however, were more likely to remain proximate to rivers where they were tagged throughout the summer. A majority of fish migrated west from their rivers of origin, primarily moving between estuarine environments. Individuals occupied estuaries for several days between bouts of marine movement, and these periods of residency coincided with spring tides in some estuaries. We also recorded increased numbers of detections on receivers located less than 1.5 km from the coast, indicating a preference for nearshore habitats. Finally, we report evidence of extensive stock mixing throughout the summer, including at known fishing locations and periods, a finding with implications for fisheries management. [ABSTRACT FROM AUTHOR]

Where anadromous fishes occur in the Canadian Arctic, they provide the mainstay of local subsistence fisheries of varying intensities. Many of these fisheries harvest a mixture of stocks at discrete locations and it is often not known which stocks, specifically, are being harvested and to what extent. In the Darnley Bay area of the Northwest Territories, Arctic char, Salvelinus alpinus, in particular have long provided an important subsistence resource to residents of Paulatuk, and char from two systems (the Hornaday and Brock Rivers) are thought to contribute to the coastal fishery for this species. Genetic mixed-stock analysis (GMA) is routinely applied for resolving stock contributions to such fisheries, yet studies incorporating GMA to understand specifically which stocks are being harvested in the Canadian Arctic, and to what extent, are relatively scarce. In this study, we assayed microsatellite DNA variation among 987 Arctic char from two important coastal subsistence fisheries and several inland sampling locations in the Darnley Bay area to (1) assess the degree of genetic structuring between the Hornaday and Brock Rivers and (2) resolve the proportional contributions of these stocks to coastal mixed-stock fisheries in the region using GMA. Overall, genetic differentiation was relatively high and significant (? = 0.117; 95% C.I. = 0.097-0.142) among baseline sampling locations. Overall patterns of genetic stock structure also support previous hypotheses that additional life history types (e.g., landlocked or freshwater-resident char, or both) exist in the Hornaday system, as indicated by elevated levels of genetic differentiation between some of our sampling locations. The GMA suggested that, while both river systems contribute to the coastal fishery, catches were dominated by Arctic char from the Hornaday River, which highlights the importance of this system. All told, our results may be relevant to the management of the subsistence fishery in Darnley Bay and for furthering the collective understanding of char biodiversity and life history variation in the Canadian Arctic. [ABSTRACT FROM AUTHOR]

The northern Dolly Varden ( Salvelinus malma malma) displays variable life-history types and occupies freshwater habitats with varying levels of connectivity. Here, we assayed microsatellite DNA variation in northern Dolly Varden from the western Canadian Arctic to resolve landscape and life-history variables driving variation in genetic diversity and population structure. Overall, genetic variation was highest in anadromous populations and lowest in those isolated above waterfalls, with stream-resident forms intermediate between the two. Anadromous and isolated populations were genetically divergent from each other, while no genetic differentiation was detectable between sympatric anadromous and stream-resident forms. Population structure was stable over 25 years, hierarchically organized, and conformed to an isolation-by-distance pattern, but stream-isolated forms often deviated from these patterns. Gene flow occurred primarily among Yukon North Slope populations and between sympatric anadromous and resident forms. These results were sex-dependent to some extent, but were influenced more by reproductive status and life history. Our study provides novel insights into the life history, population demographic, and habitat variables that shape the distribution of genetic variation and population structure in Arctic fluvial habitats while providing a spatial context for management and conservation. [ABSTRACT FROM AUTHOR]

Dispersal can influence the process of local adaptation, particularly when the dispersers successfully breed in the non-natal habitat. Anadromous Arctic char ( Salvelinus alpinus) display a complex migratory behaviour that makes the distinction between breeding and nonbreeding dispersal especially important. This species does not reproduce every year, but individuals must migrate to fresh water to overwinter such that a large proportion of fish running up-river are not in breeding condition and have no potential for gene flow. We used a genetic assignment approach to identify dispersers among populations of char from Baffin Island, Canada. Estimates of dispersal varied between 15.8% and 25.5% depending on the assignment method, suggesting that Arctic char disperse at a higher rate than other salmonids. Nonbreeding individuals were more likely to use non-natal habitats than breeding individuals, thus resulting in estimates of dispersal that overestimate the potential for gene flow among populations. Finally, we parameterized a population genetic model showing that gene flow is probably sufficiently low to allow for local adaptation among populations, given realistic selection coefficients. Our results underscore the importance of understanding patterns of dispersal to appropriately evaluate their potential consequences for local adaptation and management. [ABSTRACT FROM AUTHOR]

Parapatric freshwater and anadromous parasitic lampreys (Petromyzontiformes) from southwestern Vancouver Island, British Columbia, have been described as distinct taxa (Vancouver lamprey ( (Beamish, 1982)) and Pacific lamprey ( (Richardson, 1836)), respectively), using morphology, life history, and physiology. We tested for genetic differentiation at microsatellite DNA loci between these taxa and similar freshwater parasitic lampreys from two other lakes. The number of alleles and expected heterozygosity averaged 3.8 and 0.50, respectively, across loci and populations, and anadromous populations were more variable than freshwater populations. Population subdivision was moderate ( FST = 0.096, P < 0.001) and 3% of the total variation was found between taxa and 1.7% was found among populations within taxa (both P < 0.001). Parapatric freshwater and anadromous parasitic lampreys separated by a maximum of 40 km were more distinct (mean FST = 0.042) than were anadromous populations located 800 km from one another (mean FST = 0.012). Localities within lakes with parasitic freshwater lampreys, however, showed little differentiation ( FST = 0.0-0.08). Our data support recognizing E. macrostomus and E. tridentatus as distinct species, but similar levels of differentiation between these taxa and other freshwater parasitic lampreys suggest a species complex where the taxonomy remains unclear. [ABSTRACT FROM AUTHOR]

We assayed microsatellite DNA variation among 1013 broad whitefish. Coregonus nasus. from 36 localities within the lower Mackenzie River (Northwest Territories. Canada) to provide the first assessment of fine-scale population structuring of broad whitefish in this large system. Among sampling locations, averaged across all loci, the number of alleles ranged from 3.00 to 6.71 and heterozygosity averaged 0.54. Population subdivision was generally low. but significant (θ = 0.026. P < 0.05), although pairwise comparisons indicated that overall significance was heavily influenced by comparisons between anadromous and lacustrine groups. Bayesian-based STRUCTURE analysis suggested that there are two main genetic groups within our study area: anadromous and lacustrine broad whitefish. A mixture analysis indicated that all populations contribute to the lower Mackenzie River subsistence fishery, yet catches were dominated by Peel River fish, highlighting the importance of this tributary. Our data also supported the idea that there are several units of conservation among Mackenzie River system broad whitefish populations and that management strategies should be implemented accordingly. [ABSTRACT FROM AUTHOR]

In a polyphenic species, differences in resource use are expected among ecotypes, and homogeneity in resource use is expected within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether specialization of trophic resources by individuals occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within this lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large‐sized individuals and other piscivore individuals. We demonstrated that individual trophic specialization can occur within an ecotype inhabiting a geologically young system (8,000–10,000 yr BP), a lake that sustains high levels of phenotypic diversity of lake trout overall. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes. [ABSTRACT FROM AUTHOR]

A range of organisms, from plankton to fish, commonly shift their habitat distributions horizontally or vertically due to predation risk. Juvenile lake trout, Salvelinus namaycush, are generally viewed as occupying deep areas of lakes to decrease predation pressure from adults. In contrast, we found that juvenile lake trout from Great Bear Lake, NT, Canada, occupied a variety of habitats and from shallow to deep depths (0–150 m), overlapping with adult lake trout. No evidence occurred for a length depth‐based segregation (e.g., ontogenetic shift). Genetic variation was also similar among juveniles in the different depth zones. However, isotopic niches and C:N ratios among juveniles showed some variability in niche widths and positions for individuals caught from the 51–150 m zone compared to juvenile individuals caught from 0–20 m and 21–50 m zones. The uniformly distributed adult lake trout in Great Bear Lake may evenly distribute predation pressure (including cannibalism) across shallow‐ and deep‐water habitats more than in other lakes. As a result, juveniles may respond to differences in foraging opportunities rather than predation risks. Juvenile lake trout did not appear to conform to the general pattern of juveniles seeking a deep‐water refuge to reduce predation risks. In contrast, juvenile lake trout of Great Bear Lake displayed broad resource use across all depths and habitats. [ABSTRACT FROM AUTHOR]

Depth is usually considered the main driver of Lake Trout intraspecific diversity across lakes in North America. Given that Great Bear Lake is one of the largest and deepest freshwater systems in North America, we predicted that Lake Trout intraspecific diversity to be organized along a depth axis within this system. Thus, we investigated whether a deep-water morph of Lake Trout co-existed with four shallow-water morphs previously described in Great Bear Lake. Morphology, neutral genetic variation, isotopic niches, and life-history traits of Lake Trout across depths (0–150 m) were compared among morphs. Due to the propensity of Lake Trout with high levels of morphological diversity to occupy multiple habitat niches, a novel multivariate grouping method using a suite of composite variables was applied in addition to two other commonly used grouping methods to classify individuals. Depth alone did not explain Lake Trout diversity in Great Bear Lake; a distinct fifth deep-water morph was not found. Rather, Lake Trout diversity followed an ecological continuum, with some evidence for adaptation to local conditions in deep-water habitat. Overall, trout caught from deep-water showed low levels of genetic and phenotypic differentiation from shallow-water trout, and displayed higher lipid content (C:N ratio) and occupied a higher trophic level that suggested an potential increase of piscivory (including cannibalism) than the previously described four morphs. Why phenotypic divergence between shallow- and deep-water Lake Trout was low is unknown, especially when the potential for phenotypic variation should be high in deep and large Great Bear Lake. Given that variation in complexity of freshwater environments has dramatic consequences for divergence, variation in the complexity in Great Bear Lake (i.e., shallow being more complex than deep), may explain the observed dichotomy in the expression of intraspecific phenotypic diversity between shallow- vs. deep-water habitats. The ambiguity surrounding mechanisms driving divergence of Lake Trout in Great Bear Lake should be seen as reflective of the highly variable nature of ecological opportunity and divergent natural selection itself. [ABSTRACT FROM AUTHOR]

Using massively parallel sequencing data from two species with different life history traits, American lobster ( Homarus americanus) and Arctic Char ( Salvelinus alpinus), we highlight how an unbalanced sex ratio in the samples and a few sex-linked markers may lead to false interpretations of population structure and thus to potentially erroneous management recommendations. Here, multivariate analyses revealed two genetic clusters separating samples by sex instead of by expected spatial variation: inshore and offshore locations in lobster, or east and west locations in Arctic Char. To further investigate this, we created several subsamples artificially varying the sex ratio in the inshore/offshore and east/west groups and then demonstrated that significant genetic differentiation could be observed despite panmixia in lobster, and that FST values were overestimated in Arctic Char. This pattern was due to 12 and 94 sex-linked markers driving differentiation for lobster and Arctic Char, respectively. Removing sex-linked markers led to nonsignificant genetic structure in lobster and a more accurate estimation of FST in Arctic Char. The locations of these markers and putative identities of genes containing or nearby the markers were determined using available transcriptomic and genomic data, and this provided new information related to sex determination in both species. Given that only 9.6% of all marine/diadromous population genomic studies to date have reported sex information, we urge researchers to collect and consider individual sex information. Sex information is therefore relevant for avoiding unexpected biases due to sex-linked markers as well as for improving our knowledge of sex determination systems in nonmodel species. [ABSTRACT FROM AUTHOR]

[Display omitted] • Stable isotopes and highly branched isoprenoids were studied in a coastal Arctic food web. • Ringed seals occupied the trophic position of 4.8. • δ34S of higher trophic level pelagic organisms indicated reliance on both benthic and pelagic food sources. • 53 ± 22.2 % of marine mammal diet is derived from carbon fixed by ice algae. • Climate change could significantly threaten ice algal production and alter Arctic coastal food webs. Climate-driven alterations of the marine environment are most rapid in Arctic and subarctic regions, including Hudson Bay in northern Canada, where declining sea ice, warming surface waters and ocean acidification are occurring at alarming rates. These changes are altering primary production patterns that will ultimately cascade up through the food web. Here, we investigated (i) the vertical trophic structure of the Southampton Island marine ecosystem in northern Hudson Bay, (ii) the contribution of benthic and pelagic-derived prey to the higher trophic level species, and (iii) the relative contribution of ice algae and phytoplankton derived carbon in sustaining this ecosystem. For this purpose, we measured bulk stable carbon, nitrogen and sulfur isotope ratios as well as highly branched isoprenoids in samples belonging to 149 taxa, including invertebrates, fishes, seabirds and marine mammals. We found that the benthic invertebrates occupied 4 trophic levels and that the overall trophic system went up to an average trophic position of 4.8. The average δ34S signature of pelagic organisms indicated that they exploit both benthic and pelagic food sources, suggesting there are many interconnections between these compartments in this coastal area. The relatively high sympagic carbon dependence of Arctic marine mammals (53.3 ± 22.2 %) through their consumption of benthic invertebrate prey, confirms the important role of the benthic subweb for sustaining higher trophic level consumers in the coastal pelagic environment. Therefore, a potential decrease in the productivity of ice algae could lead to a profound alteration of the benthic food web and a cascading effect on this Arctic ecosystem. [ABSTRACT FROM AUTHOR]