Climate change vulnerability of Arctic char across Scandinavia.

Climate change is anticipated to cause species to shift their ranges upward and poleward, yet space for tracking suitable habitat conditions may be limited for range-restricted species at the highest elevations and latitudes of the globe. Consequently, range-restricted species inhabiting Arctic freshwater ecosystems, where global warming is most pronounced, face the challenge of coping with changing abiotic and biotic conditions or risk extinction. Here, we use an extensive fish community and environmental dataset for 1762 lakes sampled across Scandinavia (mid-1990s) to evaluate the climate vulnerability of Arctic char (Salvelinus alpinus), the world's most cold-adapted and northernly distributed freshwater fish. Machine learning models show that abiotic and biotic factors strongly predict the occurrence of Arctic char across the region with an overall accuracy of 89 percent. Arctic char is less likely to occur in lakes with warm summer temperatures, high dissolved organic carbon levels (i.e., browning), and presence of northern pike (Esox lucius). Importantly, climate warming impacts are moderated by habitat (i.e., lake area) and amplified by the presence of competitors and/or predators (i.e., northern pike). Climate warming projections under the RCP8.5 emission scenario indicate that 81% of extant populations are at high risk of extirpation by 2080. Highly vulnerable populations occur across their range, particularly near the southern range limit and at lower elevations, with potential refugia found in some mountainous and coastal regions. Our findings highlight that range shifts may give way to range contractions for this cold-water specialist, indicating the need for pro-active conservation and mitigation efforts to avoid the loss of Arctic freshwater biodiversity.

A new method for regionalization of the vertebral column in salmonids based on radiographic hallmarks.

Current procedures to establish vertebral column regionalization (e.g., histology) in fish are time consuming and difficult to apply. The aim of this study was to develop a more rapid and accurate radiology-based method for Atlantic salmon (Salmo salar). A detailed analysis of 90 animals (4 kg) led to the establishment of region-specific radiographic hallmarks. To elucidate its transferability to other salmonid species, radiography was carried out in brown trout (Salmo trutta), Arctic char (Salvelinus alpinus), rainbow trout (Oncorhynchus mykiss), pink salmon (Oncorhynchus gorbuscha), and Chinook salmon (Oncorhynchus tshawytscha). This method was also evaluated for whole ungutted fish. The vertebral column of Atlantic salmon can be subdivided into five regions (R1-R5) based on anatomy: postcranial (R1, V1, and V2), abdominal (R2, V3-V26), transitional (R3, V27-V36), caudal (R4, V37-V53), and ural (R5, V54-V59). The following specific radiographic hallmarks allow the identification of regions: (i) lack of ribs in R1, (ii) modified parapophysis of the first vertebra of R3, (iii) prominent hemal spine of the first vertebra of R4, and (iv) the separated hemal spine of the most cranial pre-ural vertebra of R5. These hallmarks were all transferable to the other salmonid species assessed. The results include a further description of various region-specific characteristics in Atlantic salmon. The method was found applicable for sedated/whole ungutted fish, verifying it as quick and easy compared to other regionalization methods. The regions defined by radiology in this study agree with the vertebral column regions recently defined for Chinook salmon (O. tshawytscha). Thus, and considering the results of this study on various salmonid species, the currently developed regionalization protocol can be generally used for salmonids.

The potential of oviduct tags and fine-scale acoustic telemetry to reveal the timing and location of spawning in Arctic salmonids (Salvelinus spp.).

Identifying and characterizing spawning locations are paramount for the protection of critical fish habitats but can be challenging, particularly in remote locations. Using the underexplored oviduct-tagging technique, we aimed to identify the timing and location of spawning for wild Arctic char (Salvelinus alpinus) and lake trout (Salvelinus namaycush) in two high-Arctic lakes in Nunavut. Specifically, Innovasea V7 acoustic telemetry transmitters were inserted into the oviducts of 13 Arctic char and 4 lake trout, and the timing and location of tag expulsion were determined using a fine-scale positioning system. Twenty Arctic char and 20 lake trout were also tagged with abdominal V16 transmitters, and 10 of them were paired with the oviduct tags, to further study the behavior of individual fish during the spawning season. Oviduct tags from four Arctic char and one lake trout could be used to assess the timing and location of spawning. Spawning anadromous Arctic char drastically reduced their activity and remained proximate to their presumed spawning location immediately before and for months after spawning. In contrast, a non-anadromous (i.e., freshwater resident) Arctic char and a lake trout showed little to no reduction in activity around presumed spawning events. Because of the highlighted sedentary behavior of inferred spawning anadromous Arctic char implanted with both abdominal and oviduct tags, we could also infer potential spawning based on the behavior of individuals equipped only with abdominal tags. Spawning areas identified via telemetry also aligned well with Inuit knowledge of those lakes. This is the first field study to use acoustic oviduct and abdominal tags coupled with a fine-scale positioning system. Despite a limited success rate of ejection, the study reveals the strong potential of the method to study spawning habitat and timing, particularly in remote areas.

Contrasting intra-individual variation in size-based trophic and habitat shifts for two coastal Arctic fish species.

Within and among species variation in trophic and habitat shifts with body size can indicate the potential adaptive capacity of species to ecosystem change. In Arctic coastal ecosystems, which experience dramatic seasonal shifts and are undergoing rapid change, quantifying the trophic flexibility of coastal fishes with different migratory tactics has received limited attention. We examined the relationships among body length and condition (Fulton's K, phase angle from Bioelectrical Impedance Analysis) with trophic and habitat shifts (differences in δ15N and δ13C between blood tissues with different turnover rates) of two abundant and culturally important species, anadromous Arctic char (Salvelinus alpinus, n = 38) and sedentary Greenland cod (Gadus ogac, n = 65) during summer in coastal marine waters near Ulukhaktok, Northwest Territories, Canada. Habitat shifts (δ13C) increased with length (i.e., pelagic to benthic-littoral) and crossed-equilibrium (zero) at mid-sizes for both species. Seasonal trophic shifts (δ15N) were generally positive (i.e., increasing trophic level) for Arctic char and negative for Greenland cod. As hypothesised, intra-individual variation in size-based trophic shifts (δ15N-length residuals) increased with length for Arctic char. However, there were no trends with length in Greenland cod. Our findings highlight the importance of flexibility through ontogeny and mobility for Arctic char, whereas Greenland cod were generalist to localized prey and habitat across all sizes. The significant effect of body condition (phase angle) on size-based trophic shifts in Arctic char, and size-based habitat shifts in Greenland cod, highlight the potential trade-offs of contrasting life history strategies and capacity for ontogenetic niche plasticity.

Fatty Acid Profile of Juvenile Arctic Char (Salvelinus alpinus Complex) from Natural Ecosystems and Aquaculture.

Significant differences in the fatty acid composition of the muscle tissue of juvenile Arctic char Salvelinus alpinus (Linnaeus, 1758) from the natural habitat (Lake Sobach'e) and aquaculture, as well as juveniles of the anadromous form of char (malma) Salvelinus malma (Walbaum, 1792) from the Avacha River were found. The observed differences between aquaculture and wild juvenile char were associated with different food sources. The muscle tissue of juvenile char from natural habitat was characterized by significantly higher levels of fatty acids-biomarkers of diatoms, as well as biomarkers of marine copepods in the anadromous form. In the fatty acid composition of juvenile char from aquaculture, significantly higher levels of linoleic acid were revealed, as well as long-chain monounsaturated acids, the source of which could be aquaculture feed. The identified differences did not have a significant effect on the content of eicosapentaenoic and docosahexaenoic acids in the muscle tissue of juvenile aquaculture and wild char. The content of biochemically valuable omega 3 polyunsaturated fatty acids in juvenile char from natural ecosystems and aquaculture was similar.

Element concentrations, histology and serum biochemistry of arctic char (Salvelinus alpinus) and shorthorn sculpins (Myoxocephalus scorpius) in northwest Greenland.

The increasing exploratory efforts in the Greenland mineral industry, and in particular, the proposed rare earth element (REE) mining projects, requires an urgent need to generate data on baseline REE concentrations and their potential environmental impacts. Herein, we have investigated REE concentrations in anadromous Arctic char (Salvelinus alpinus) and shorthorn sculpins (Myoxocephalus scorpius) from uncontaminated sites in Northwest Greenland, along with the relationships between the element concentrations in gills and liver, and gill histology and serum biochemical parameters. Concentrations of arsenic, silver, cadmium, cerium, chromium, copper, dysprosium, mercury, lanthanum, neodymium, lead, selenium, yttrium, and zinc in gills, liver and muscle are presented. No significant statistical correlations were observed between element concentrations in different organs and gill histology or serum biochemical parameters. However, we observed positive relationships between age and histopathology, emphasizing the importance of including age as a co-variable in histological studies of fish. Despite no element-induced effects were observed, this study is considered an important baseline study, which can be used as a reference for the assessment of impacts of potential future REE mine sites in Greenland.

Overwintering ecology and movement of anadromous Arctic char (Salvelinus alpinus) in a large, ice-covered river in the Canadian Arctic.

Arctic char (Salvelinus alpinus) is a facultatively anadromous fish species that is critically important to many Inuit communities in the Canadian Arctic. Plasticity in life history has allowed the species to persist in a diversity of challenging Holarctic environments. Despite their ecological and cultural importance and their presence in aquatic ecosystems that are ice-covered for much of the year, few under-ice studies of Arctic char have been conducted. Most winter studies of adult Arctic char have focused on lakes, where they typically overwinter. Several populations of Arctic char, however, overwinter in large river systems, and subsistence fishers have reported that Arctic char overwinter in the lower reaches of the Coppermine River. The Coppermine River is a large Arctic river that flows into Coronation Gulf near Kugluktuk, Nunavut, Canada. The authors used acoustic telemetry to investigate the overwintering ecology of Arctic char in the region. Consistent with local knowledge, they detected Arctic char overwintering within the fluvial environment of the Coppermine River from 2018 to 2020. Unlike other fluvial environments known to be used by overwintering Arctic char, the lower reaches of the Coppermine River are completely ice-covered throughout the winter, are of moderate depths (3.8-14.1 m) and have no known groundwater inputs. Acoustic telemetry observations indicated long-distance movement (7-8 km) within the river in early winter (October) in response to dynamic ice formation. Under-ice movement generally declined 2 weeks after river freeze-up but continued throughout winter in the lower 5 km of the river, where there were fewer under-ice disturbances. Migration into the marine environment before river ice break-up (June), as well as winter (November-May) movements into and within the marine environment, was unexpectedly observed for some fish. Under-ice use of the marine environment is unusual for Arctic char at the distances observed (up to 18 km) and has not previously been documented at the temperatures (fish body temperatures from -0.76 to 1.90°C) observed. Results allow further understanding of the diverse life-history tactics employed by Arctic char and lay a foundation for future research into fluvial and other diverse overwintering tactics employed by the species.

Muscular microsporidian infection in Arctic char Salvelinus alpinus from two lakes in Nunavik, Quebec, Canada.

Arctic char Salvelinus alpinus is an important cultural and subsistence resource for Inuit communities. Muscular infections by microsporidia were diagnosed for the first time in Arctic char originating from 2 different lakes in Nunavik (Quebec, Canada). The consumption of these infected fish was associated with digestive tract disorders in people. To better characterize microsporidiosis in these char populations, a cross-sectional study was conducted on 91 fish. The microsporidium was classified as a member of the Microsporidium collective genus by morphological evaluation and phylogenetic analysis using small subunit ribosomal DNA sequence data. The presence and severity of infection were determined histologically. Microsporidian infection occurred in 61% of the fish (56/91) and was significantly associated with an increase in their age, length and weight. The severity of infection (percentage of muscle area affected by microsporidia) was mild in most cases (<1% of the total muscle area). Based on multiple linear regression modeling, the severity of infection was significantly greater in females and negatively correlated with the body condition. Despite a high prevalence, the low pathogenicity of the infection suggests that microsporidiosis has little impact on these char populations. Moreover, since digestive-tract disorders following ingestion of fish infected by microsporidia have never been reported in humans, it seems unlikely that it was responsible for the reported clinical signs. Anisakid larvae are occasionally observed in these char populations. Digestive-tract infection associated with ingestion of these larvae should thus be considered as a potential differential diagnosis in these Inuit communities.

The thermal acclimation potential of maximum heart rate and cardiac heat tolerance in Arctic char (Salvelinus alpinus), a northern cold-water specialist.

Increasing heart rate (ƒH) is a central, if not primary mechanism used by fishes to support their elevated tissue oxygen consumption during acute warming. Thermal acclimation can adjust this acute response to improve cardiac performance and heat tolerance under the prevailing temperatures. We predict that such acclimation will be particularly important in regions undergoing rapid environmental change such as the Arctic. Therefore, we acclimated Arctic char (Salvelinus alpinus), a high latitude, cold-adapted salmonid, to ecologically relevant temperatures (2, 6, 10, 14 and 18 °C) and examined how thermal acclimation influenced their cardiac heat tolerance by measuring the maximum heart rate (ƒHmax) response to acute warming. As expected, acute warming increased ƒHmax in all Arctic char before ƒHmax reached a peak and then became arrhythmic. The peak ƒHmax, and the temperature at which peak ƒHmax (Tpeak) and that at which arrhythmia first occurred (Tarr) all increased progressively (+33%, 49% and 35%, respectively) with acclimation temperature from 2 to 14 °C. When compared at the same test temperature ƒHmax also decreased by as much as 29% with increasing acclimation temperature, indicating significant thermal compensation. The upper temperature at which fish first lost their equilibrium (critical thermal maximum: CTmax) also increased with acclimation temperature, albeit to a lesser extent (+11%). Importantly, Arctic char experienced mortality after several weeks of acclimation at 18 °C and survivors did not have elevated cardiac thermal tolerance. Collectively, these findings suggest that if wild Arctic char have access to suitable temperatures (<18 °C) for a sufficient duration, warm acclimation can potentially mitigate some of the cardiorespiratory impairments previously documented during acute heat exposure.

Trophic structure of apex fish communities in closed versus leaky lakes of arctic Alaska.

Despite low species diversity and primary production, trophic structure (e.g., top predator species, predator size) is surprisingly variable among Arctic lakes. We investigated trophic structure in lakes of arctic Alaska containing arctic char Salvelinus alpinus using stomach contents and stable isotope ratios in two geographically-close but hydrologically-distinct lake clusters to investigate how these fish may interact and compete for limited food resources. Aside from different lake connectivity patterns ('leaky' versus 'closed'), differing fish communities (up to five versus only two species) between lake clusters allowed us to test trophic hypotheses including: (1) arctic char are more piscivorous, and thereby grow larger and obtain higher trophic positions, in the presence of other fish species; and, (2) between arctic char size classes, resource polymorphism is more prominent, and thereby trophic niches are narrower and overlap less, in the absence of other predators. Regardless of lake cluster, we observed little direct evidence of arctic char consuming other fishes, but char were larger (mean TL = 468 vs 264 mm) and trophic position was higher (mean TP = 4.0 vs 3.8 for large char) in lakes with other fishes. Further, char demonstrated less intraspecific overlap when other predators were present whereas niche overlap was up to 100% in closed, char only lakes. As hydrologic characteristics (e.g., lake connectivity, water temperatures) will change across the Arctic owing to climate change, our results provide insight regarding potential concomitant changes to fish interactions and increase our understanding of lake trophic structure to guide management and conservation goals.

Piscine orthoreovirus-3 is prevalent in wild seatrout (Salmo trutta L.) in Norway.

In 2017, a PCR-based survey for Piscine orthoreovirus-3 (PRV-3) was conducted in wild anadromous and non-anadromous salmonids in Norway. In seatrout (anadromous Salmo trutta L.), the virus was present in 16.6% of the fish and in 15 of 21 investigated rivers. Four of 221 (1.8%) Atlantic salmon (Salmo salar L.) from three of 15 rivers were also PCR-positive, with Ct-values indicating low amounts of viral RNA. All anadromous Arctic char (Salvelinus alpinus L.) were PCR-negative. Neither non-anadromous trout (brown trout) nor landlocked salmon were PRV-3 positive. Altogether, these findings suggest that in Norway PRV-3 is more prevalent in the marine environment. In contrast, PRV-3 is present in areas with intensive inland farming in continental Europe. PRV-3 genome sequences from Norwegian seatrout grouped together with sequences from rainbow trout (Oncorhynchus mykiss Walbaum) in Norway and Coho salmon (Oncorhynchus kisutch Walbaum) in Chile. At present, the origin of the virus remains unknown. Nevertheless, the study highlights the value of safeguarding native fish by upholding natural and artificial barriers that hinder introduction and spread, on a local or national scale, of alien fish species and their pathogens. Accordingly, further investigations of freshwater reservoirs and interactions with farmed salmonids are warranted.

First confirmation of salmonid alphavirus infection in Arctic char Salvelinus alpinus and in Austria.

To date, sleeping disease (SD) caused by salmonid alphavirus 2 (SAV 2) has been reported in freshwater rainbow trout Oncorhynchus mykiss and Atlantic salmon Salmo salar. This study describes for the first time the occurrence of SD in farm-reared Arctic char Salvelinus alpinus and the occurrence of SAV in Austria. Clinical symptoms were indicative of the disease, and the diagnosis was confirmed by histopathology, infectivity in first passages of CHSE-214 cells and PCR. The phylogenetic analysis of the amplified SAV-nonstructural protein-3 (nsP3) fragment revealed the affiliation to the SAV 2 genotype.

A survey of salmon gill poxvirus (SGPV) in wild salmonids in Norway.

In 2016, the Norwegian health monitoring programme for wild salmonids conducted a real-time PCR-based screening for salmon gill poxvirus (SGPV) in anadromous Arctic char (Salvelinus alpinus L.), anadromous and non-anadromous Atlantic salmon (Salmo salar L.) and trout (Salmo trutta L.). SGPV was widely distributed in wild Atlantic salmon returning from marine migration. In addition, characteristic gill lesions, including apoptosis, were detected in this species. A low amount of SGPV DNA, as indicated by high Ct-values, was detected in anadromous trout, but only in fish cohabiting with SGPV-positive salmon. SGPV was not detected in trout and salmon from non-anadromous water courses, and thus seems to be primarily linked to the marine environment. This could indicate that trout are not a natural host for the virus. SGPV was not detected in Arctic char but, due to a low sample size, these results are inconclusive. The use of freshwater from anadromous water sources may constitute a risk of introducing SGPV to aquaculture facilities. Moreover, SGPV-infected Atlantic salmon farms will hold considerable potential for virus propagation and spillback to wild populations. This interaction should therefore be further investigated.

Construction of Aeromonas salmonicida subsp. achromogenes AsaP1-toxoid strains and study of their ability to induce immunity in Arctic char, Salvelinus alpinus L.

The metalloendopeptidase AsaP1 is one of the major extracellular virulence factors of A. salmonicida subsp. achromogenes, expressed as a 37-kDa pre-pro-peptide and processed to a 19-kDa active peptide. The aim of this study was to construct mutant strains secreting an AsaP1-toxoid instead of AsaP1-wt, to study virulence of these strains and to test the potency of the AsaP1-toxoid bacterin and the recombinant AsaP1-toxoids to induce protective immunity in Arctic char. Two A. salmonicida mutants were constructed that secrete either AsaP1E294A or AsaP1Y309F . The secreted AsaP1Y309F -toxoid had weak caseinolytic activity and was processed to the 19-kDa peptide, whereas the AsaP1E294A -toxoid was found as a 37-kDa pre-pro-peptide suggesting that AsaP1 is auto-catalytically processed. The LD50 of the AsaP1Y309F -toxoid mutant in Arctic char was significantly higher than that of the corresponding wt strain, and LD50 of the AsaP1E294A -toxoid mutant was comparable with that of an AsaP1-deficient strain. Bacterin based on AsaP1Y309F -toxoid mutant provided significant protection, comparable with that induced by a commercial polyvalent furunculosis vaccine. Detoxification of AsaP1 is very hard, expensive and time consuming. Therefore, an AsaP1-toxoid-secreting mutant is more suitable than the respective wt strain for production of fish bacterins aimed to protect against atypical furunculosis.

The gut microbiome of farmed Arctic char (Salvelinus alpinus) is shaped by feeding stage and nutrient presence.

The gut microbiome plays an important role in maintaining health and productivity of farmed fish. However, the functional role of most gut microorganisms remains unknown. Identifying the stable members of the gut microbiota and understanding their functional roles could aid in the selection of positive traits or act as a proxy for fish health in aquaculture. Here, we analyse the gut microbial community of farmed juvenile Arctic char (Salvelinus alpinus) and reconstruct the metabolic potential of its main symbionts. The gut microbiota of Arctic char undergoes a succession in community composition during the first weeks post-hatch, with a decrease in Shannon diversity and the establishment of three dominant bacterial taxa. The genome of the most abundant bacterium, a Mycoplasma sp., shows adaptation to rapid growth in the nutrient-rich gut environment. The second most abundant taxon, a Brevinema sp., has versatile metabolic potential, including genes involved in host mucin degradation and utilization. However, during periods of absent gut content, a Ruminococcaceae bacterium becomes dominant, possibly outgrowing all other bacteria through the production of secondary metabolites involved in quorum sensing and cross-inhibition while benefiting the host through short-chain fatty acid production. Whereas Mycoplasma is often present as a symbiont in farmed salmonids, we show that the Ruminococcaceae species is also detected in wild Arctic char, suggesting a close evolutionary relationship between the host and this symbiotic bacterium.

Migration timing and marine space use of an anadromous Arctic fish (Arctic Char, Salvelinus alpinus) revealed by local spatial statistics and network analysis.

BACKGROUND: The ice-free season (typically late-June to early-October) is crucial for anadromous species of fish in the Arctic, including Arctic Char (Salvelinus alpinus), which must acquire adequate resources for growth, reproduction, and survival during a brief period of feeding in the marine environment. Arctic Char is an important food fish for Inuit communities across the Arctic. Understanding drivers and patterns of migration in the marine environment is thus essential for conservation and management of the species. METHODS: We used passive acoustic telemetry to characterize migration patterns of 51 individual anadromous Arctic Char during the ice-free season in the marine environment of Coronation Gulf (Nunavut, Canada; 2019-2022). Based on recent genetic evidence, some tagged individuals were likely Dolly Varden (Salvelinus malma malma), a closely related species to Arctic Char. Using local Getis G* and network analysis, we described movement patterns and identified high-use locations in the marine environment. We also related freshwater overwintering location to migration timing and movement pattern. RESULTS: Comparing groups of fish that overwintered in distinct locations, we found: (i) limited evidence that marine movements were associated with overwintering location; (ii) minor differences in use of marine space; and, (iii) timing of freshwater return differed significantly between overwintering groups, and was related to length and difficulty of the migratory pathway in freshwater. Results from both network analysis and local Getis G* revealed that, regardless of overwintering location, coastal locations were highly used by fish. CONCLUSIONS: Overwintering locations, and the migratory routes to access overwintering locations, affect the timing of freshwater return. Preference of fish for coastal marine locations is likely due to abundance of forage and patterns in break-up of sea ice. Similarities in marine space use and movement patterns present challenges for managing this and other mixed stock fisheries of anadromous Salvelinus spp. Absences or periods of time when fish were not detected prevented comprehensive assessment of movement patterns. Local Getis G*, a local indicator of spatial association, is a helpful tool in identifying locations associated with absences in acoustic telemetry arrays, and is a complementary method to network analysis.

Characterization of gill bacterial microbiota in wild Arctic char (Salvelinus alpinus) across lakes, rivers, and bays in the Canadian Arctic ecosystems.

Teleost gill mucus has a highly diverse microbiota, which plays an essential role in the host's fitness and is greatly influenced by the environment. Arctic char (Salvelinus alpinus), a salmonid well adapted to northern conditions, faces multiple stressors in the Arctic, including water chemistry modifications, that could negatively impact the gill microbiota dynamics related to the host's health. In the context of increasing environmental disturbances, we aimed to characterize the taxonomic distribution of transcriptionally active taxa within the bacterial gill microbiota of Arctic char in the Canadian Arctic in order to identify active bacterial composition that correlates with environmental factors. For this purpose, a total of 140 adult anadromous individuals were collected from rivers, lakes, and bays belonging to five Inuit communities located in four distinct hydrologic basins in the Canadian Arctic (Nunavut and Nunavik) during spring (May) and autumn (August). Various environmental factors were collected, including latitudes, water and air temperatures, oxygen concentration, pH, dissolved organic carbon (DOC), salinity, and chlorophyll-a concentration. The taxonomic distribution of transcriptionally active taxa within the gill microbiota was quantified by 16S rRNA gene transcripts sequencing. The results showed differential bacterial activity between the different geographical locations, explained by latitude, salinity, and, to a lesser extent, air temperature. Network analysis allowed the detection of a potential dysbiosis signature (i.e., bacterial imbalance) in fish gill microbiota from Duquet Lake in the Hudson Strait and the system Five Mile Inlet connected to the Hudson Bay, both showing the lowest alpha diversity and connectivity between taxa.IMPORTANCEThis paper aims to decipher the complex relationship between Arctic char (Salvelinus alpinus) and its symbiotic microbial consortium in gills. This salmonid is widespread in the Canadian Arctic and is the main protein and polyunsaturated fatty acids source for Inuit people. The influence of environmental parameters on gill microbiota in wild populations remains poorly understood. However, assessing the Arctic char's active gill bacterial community is essential to look for potential pathogens or dysbiosis that could threaten wild populations. Here, we concluded that Arctic char gill microbiota was mainly influenced by latitude and air temperature, the latter being correlated with water temperature. In addition, a dysbiosis signature detected in gill microbiota was potentially associated with poor fish health status recorded in these disturbed environments. With those results, we hypothesized that rapid climate change and increasing anthropic activities in the Arctic might profoundly disturb Arctic char gill microbiota, affecting their survival.

Divergent Temporal Trends of Mercury in Arctic Char from Paired Lakes Influenced by Climate-Related Drivers.

Climate-driven changes including rising air temperatures, enhanced permafrost degradation, and altered precipitation patterns can have profound effects on contaminants, such as mercury (Hg), in High Arctic lakes. Two physically similar lakes, East Lake and West Lake at the Cape Bounty Arctic Watershed Observatory on Melville Island, Nunavut, Canada are being affected by climate change differently. Both lakes have experienced permafrost degradation in their catchments; however, West Lake has also undergone multiple underwater Mass Movement Events (MMEs; beginning in fall 2008), leading to a sustained 50-fold increase in turbidity. This provided the unique opportunity to understand the potential impacts of permafrost degradation and other climate-related effects on Hg concentrations and body condition of landlocked Arctic char (Salvelinus alpinus), an important sentinel species across the Circum-Arctic. Our objectives were to assess temporal trends in char Hg concentrations and to determine potential mechanisms driving the trends. There was a significant decrease in Hg concentrations in East Lake char, averaging 6.5%/year and 3.8%/year for length-adjusted and age-adjusted means, respectively, from 2008 to 2019. Conversely, in West Lake there was a significant increase, averaging 7.9%/year and 8.0%/year for length-adjusted and age-adjusted mean Hg concentrations, respectively, for 2009 to 2017 (the last year with sufficient sample size). The best predictors of length-adjusted Hg concentrations in West Lake were carbon and nitrogen stable isotope ratios, indicating a shift in diet including possible dietary starvation brought on by the profound increase in lake turbidity. Our study provides an example of how increasing lake turbidity, a likely consequence of climate warming in Arctic lakes, may influence fish condition and Hg concentrations. Environ Toxicol Chem 2023;42:2712-2725. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Mercury at the top of the world: A 31-year record of mercury in Arctic char in the largest High Arctic lake, linked to atmospheric mercury concentrations and climate oscillations.

Lake Hazen, the largest lake north of the Arctic circle, is being impacted by mercury (Hg) pollution and climate change. The lake is inhabited by two morphotypes of land-locked Arctic char (Salvelinus alpinus), a sensitive indicator species for pollution and climatic impacts. The objectives of this study were to describe the trends in Hg concentration over time and to determine the relationship of climate to length-at-age and Hg concentrations in each char morphotype, as well as the relationship to atmospheric Hg measurements at a nearby monitoring station. Results for Hg in char muscle were available from 20 sampling years over the period 1990 to 2021. We found significant declines in Hg concentrations for both morphotypes during the 31-year study period. Increased rain and earlier freeze-up of lake ice during the summer growing season was linked to increased length-at-age in both char morphotypes. For the large morphotype, higher total gaseous Hg in the fall and winter seasons was related to higher concentrations of Hg in char, while increased glacial runoff was related to decreases in char Hg. For the small morphotype char, increased snow and snow accumulation in the fall season were linked to declines in char Hg concentration. The Atlantic Multidecadal Oscillation and Arctic Oscillation were positively related to the large char Hg trend and Arctic Oscillation was positively related to the small char Hg trend. Significant trend relationships between atmospheric Hg and Hg in biota in remote regions are rare and uniquely valuable for evaluation of the effectiveness of the Minamata Convention and related monitoring efforts.

Investigating the morphological and genetic divergence of arctic char (Salvelinus alpinus) populations in lakes of arctic Alaska.

Polymorphism facilitates coexistence of divergent morphs (e.g., phenotypes) of the same species by minimizing intraspecific competition, especially when resources are limiting. Arctic char (Salvelinus sp.) are a Holarctic fish often forming morphologically, and sometimes genetically, divergent morphs. In this study, we assessed the morphological and genetic diversity and divergence of 263 individuals from seven populations of arctic char with varying length-frequency distributions across two distinct groups of lakes in northern Alaska. Despite close geographic proximity, each lake group occurs on landscapes with different glacial ages and surface water connectivity, and thus was likely colonized by fishes at different times. Across lakes, a continuum of physical (e.g., lake area, maximum depth) and biological characteristics (e.g., primary productivity, fish density) exists, likely contributing to characteristics of present-day char populations. Although some lakes exhibit bimodal size distributions, using model-based clustering of morphometric traits corrected for allometry, we did not detect morphological differences within and across char populations. Genomic analyses using 15,934 SNPs obtained from genotyping by sequencing demonstrated differences among lake groups related to historical biogeography, but within lake groups and within individual lakes, genetic differentiation was not related to total body length. We used PERMANOVA to identify environmental and biological factors related to observed char size structure. Significant predictors included water transparency (i.e., a primary productivity proxy), char density (fish·ha-1), and lake group. Larger char occurred in lakes with greater primary production and lower char densities, suggesting less intraspecific competition and resource limitation. Thus, char populations in more productive and connected lakes may prove more stable to environmental changes, relative to food-limited and closed lakes, if lake productivity increases concomitantly. Our findings provide some of the first descriptions of genomic characteristics of char populations in arctic Alaska, and offer important consideration for the persistence of these populations for subsistence and conservation.