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Trophic polymorphism and temporal reproductive isolation are the drivers of sympatric differentiation in many fish taxa. We present a new case of ecologically based diversification of Arctic charr in a Transbaikalian mountain lake inhabited by reproductively isolated dwarf and normal forms. These forms differ in size, diets and morphology and breed, respectively, in April–May and in September–October representing a rare example of sympatric spring- and autumn-spawning charr pair. Microsatellite analysis reveals clear-cut genetic differences and low-level hybridization between them. Dwarf form charr are planktivorous and manifest uniform slow growth. Normal form charr, though genetically homogeneous, are highly heterogeneous in size-at-age. They are subdivided into omnivorous small-size and piscivorous large-size groups, which can be considered as incipient forms at an early divergence stage. As evidenced by back-calculated growth data, their size-at-age heterogeneity results from highly variable individual growth patterns, which include different combinations of slow and fast growth periods presumably associated with spawning and non-spawning years. Growth acceleration in late ontogeny may result in the transformation of some normal charr from the smaller into the larger group during their lifetime. [ABSTRACT FROM AUTHOR]

Detection of intestinal parasites in fish typically requires autopsy, resulting in the sacrifice of the fish. Here, we describe a non‐lethal method for detecting the tapeworm Eubothrium crassum in fish using anal swabs and real‐time PCR detection. Two assays were developed to detect cytochrome oxidase I (COI) mitochondrial DNA and 18S ribosomal DNA sequences of E. crassum, respectively. The assays were tested on swab samples from confirmed pathogen free Atlantic salmon (Salmo salar L.) and on samples from farmed Atlantic salmon, where the presence and intensity of parasites had been established through autopsy. The COI assay was shown to be specific to E. crassum, while the 18S assay also amplified the closely related E. salvelini, a species infecting Arctic charr (Salvelinus alpinus L.) in freshwater. The COI assay detected E. crassum in all field samples regardless of parasite load while the 18S assay failed to detect the parasite in two samples. The results thus demonstrates that this non‐lethal approach can effectively detect E. crassum and can be a valuable tool in assessing the prevalence of infection in farmed salmon, aiding in treatment decisions and evaluating treatment effectiveness. [ABSTRACT FROM AUTHOR]

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure, and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite the fact that the phenotype being essential for organism ecology and evolution. In this study, we tested the effects of heat shocks during the embryonic period on the phenotype of Arctic charr (Salvelinus alpinus). We repeatedly quantified multiple phenotypic traits, including morphology, development, and behavior, over a period of 4 months, from hatching to juvenile stage in individuals that had experienced heat shocks (+ 5°C on 24 h, seven times) during their embryonic stage and those that had not. We found that heat shocks led to smaller body size at hatching and a lower sociability. Interestingly, these effects weakened throughout the development of individuals and even reversed in the case of body size. We also found an accelerated growth rate and a higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long‐lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and the unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity. [ABSTRACT FROM AUTHOR]

Across its Holarctic range, Arctic charr (Salvelinus alpinus) populations have diverged into distinct trophic specialists across independent replicate lakes. The major aspect of divergence between ecomorphs is in head shape and body shape, which are ecomorphological traits reflecting niche use. However, whether the genomic underpinnings of these parallel divergences are consistent across replicates was unknown but key for resolving the substrate of parallel evolution. We investigated the genomic basis of head shape and body shape morphology across four benthivore–planktivore ecomorph pairs of Arctic charr in Scotland. Through genome‐wide association analyses, we found genomic regions associated with head shape (89 SNPs) or body shape (180 SNPs) separately and 50 of these SNPs were strongly associated with both body and head shape morphology. For each trait separately, only a small number of SNPs were shared across all ecomorph pairs (3 SNPs for head shape and 10 SNPs for body shape). Signs of selection on the associated genomic regions varied across pairs, consistent with evolutionary demography differing considerably across lakes. Using a comprehensive database of salmonid QTLs newly augmented and mapped to a charr genome, we found several of the head‐ and body‐shape‐associated SNPs were within or near morphology QTLs from other salmonid species, reflecting a shared genetic basis for these phenotypes across species. Overall, our results demonstrate how parallel ecotype divergences can have both population‐specific and deeply shared genomic underpinnings across replicates, influenced by differences in their environments and demographic histories. [ABSTRACT FROM AUTHOR]

This annotated bibliography highlights new Arabic-language publications in critical Arab scholarship. It includes reviews of two books. The first book, "Russia, China, and partnership for a new era: incentives and constraints" by Nouran Awadin, examines the impact of Russian-Chinese relations on the international system and the potential for a multipolar world order. The second book, "Geopolitics of the Mediterranean Basin: Delimitation of Maritime Boundaries and Issues of International Peace and Security" by a group of authors, explores the strategic importance of the Mediterranean Basin and the demarcation of maritime borders in the region. Additionally, the article provides synopses of three other new Arabic-language publications. The first book discusses the development of political and economic relations between China and Saudi Arabia, emphasizing the religious and economic significance of Saudi Arabia to China. The second book delves into the concept of equality in the Arab Islamic community, presenting arguments for and against equality and emphasizing its importance for justice. Lastly, the third book focuses on citizenship values and education, examining the rights and responsibilities of citizens and the challenges faced in promoting citizenship values in Arab pluralistic societies. [Extracted from the article]

Genetic diversity is fundamental to the adaptive potential and survival of species. Although its importance has long been recognized in science, it has a history of neglect within policy, until now. The new Global Biodiversity Framework recently adopted by the Convention on Biological Diversity, states that genetic diversity must be maintained at levels assuring adaptive potential of populations, and includes metrics for systematic monitoring of genetic diversity in so called indicators. Similarly, indicators for genetic diversity are being developed at national levels. Here, we apply new indicators for Swedish national use to one of the northernmost salmonid fishes, the Arctic charr (Salvelinus alpinus). We sequence whole genomes to monitor genetic diversity over four decades in three landlocked populations inhabiting protected alpine lakes in central Sweden. We find levels of genetic diversity, inbreeding and load to differ among lakes but remain stable over time. Effective population sizes are generally small (< 500), suggesting a limited ability to maintain adaptive variability if genetic exchange with nearby populations became eliminated. We identify genomic regions potentially shaped by selection; SNPs exhibiting population divergence exceeding expectations under drift and a putative selective sweep acting within one lake to which the competitive brown trout (Salmo trutta) was introduced during the sampling period. Identified genes appear involved in immunity and salinity tolerance. Present results suggest that genetically vulnerable populations of Arctic charr have maintained neutral and putatively adaptive genetic diversity despite small effective sizes, attesting the importance of continued protection and assurance of gene flow among populations. [ABSTRACT FROM AUTHOR]

Fish and fish tissue are effective bioindicators due to their sensitivity to pollution and are frequently used for assessing aquatic ecosystem health. Establishing baseline metal concentrations in freshwater fish tissues within aquatic ecosystems is important prior to establishing industrial activities to help determine potential future industrial impacts. Historically, North-Eastern European Russia has been an area with relatively low levels of industrial development and is still in pristine condition. In this region, the noise-to-background ratio for industrial contaminants may be disproportionately high. This study measured baseline metal concentrations in freshwater fish tissues collected from three study sites (the Bolshoi Patok, Maly Patok and Kara Rivers) in northeastern European Russia as bioindicators of overall aquatic ecosystem health. Seven fish species, namely, European Grayling, Arctic Char, Whitefish, Perch, Pike, Roach, and Peled, were studied over a three-year period between 2000 and 2003. The copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) concentrations were analysed in fish tissue samples. Metal concentrations measured in fish tissues in this study were comparable to those measured at remote sites in Alaska, the United States and Slovenia. Despite the small variation between the sampling sites, the metal concentrations were relatively low and considered to be in pristine condition. Metal concentrations measured in fish tissues in this study represent baseline conditions, which will be important for comparison against monitoring programmes should the region experience future industrial development. [ABSTRACT FROM AUTHOR]

Primary producers form the base of lake ecosystems and, due to their often short lifecycles, respond rapidly to changing conditions. As the Arctic is warming nearly four times faster than the global average, we see major shifts in environmental conditions, which impacts lake ecosystem functioning. Previous studies have found a general increase in primary productivity due to climate warming. However, few long‐term studies have included changes in phytoplankton community composition and biomass in relation to warming in Arctic lakes and it therefore remains unclear how different algal taxa and thus the community respond.We investigated how climate warming affects phytoplankton community composition, taxon richness and biomass in High Arctic lakes, using a unique 23‐year data series on phytoplankton in two shallow lakes at Zackenberg, north‐east Greenland, one with Arctic charr (Salvelinus alpinus) and one without fish. We further elucidated the role of physico‐chemical variables and zooplankton grazers in the changes observed.Few major changes were observed in phytoplankton community composition over time, but the year‐to‐year variation was large. Taxon richness did, however, increase throughout the monitoring period, and in both lakes there was a significant increase in diatom biomass coinciding with increasing conductivity. Additionally, phytoplankton biomass was greater during warmer years with earlier ice melt. We further found that nutrient levels were positively associated with the total phytoplankton biomass in both lakes, indicating that expected increased nutrient levels, due to climate change, may lead to a greater phytoplankton biomass in High Arctic lakes in the future.The large year‐to‐year variability, in both climate and environmental conditions, makes it difficult to predict weather patterns and their consequences for lake ecosystems in the Arctic region. This underlines the importance of long‐term monitoring programmes across the circumpolar Arctic and collaboration across regions and institutes within large scale studies. [ABSTRACT FROM AUTHOR]

Abstract 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.

Differentiation of foraging traits among predator populations may help explain observed variation in the structure of prey communities. However, few studies have investigated the phenotypic effects of predators on their prey in natural communities. Here, we use a comparative analysis of 78 Greenlandic lakes to examine how foraging trait variation among threespine stickleback populations can help explain variation in zooplankton community composition among lakes. We find that landscape‐scale variation in zooplankton composition was jointly explained by lake properties, such as size and water chemistry, and the presence and absence of both stickleback and arctic char. Additional variation in zooplankton community structure can be explained by stickleback jaw protrusion, a trait with known utility for foraging on zooplankton, but only in lakes where stickleback co‐occur with arctic char. Overall, our results illustrate how trait variation of predators, alongside other ecosystem properties, can influence the composition of prey communities in nature. [ABSTRACT FROM AUTHOR]

Salmonids are introduced in various ecosystems, including mountain lakes characterised by extreme environmental constraints. Although these constraints can affect salmonid body condition through direct and indirect pathways, they remain seldom explored despite their importance for understanding salmonid fitness and long‐term establishment.In order to fill this gap, we firstly fitted species‐specific weight–length relationships for three salmonid species in nine mountain lakes, and compared their allometric coefficients with those of 362 salmonid populations worldwide to identify potential differences in growth trajectory of salmonids in the studied lakes. We then investigated how thermal characteristics and lake morphometry could influence salmonid body conditions, both directly and indirectly through salmonid density, the presence of forage fish and resource densities. We calculated salmonid relative body condition Kn and used a structural equation model (SEM) to disentangle these direct and indirect effects.The values of allometric coefficients for the three species did not differ from those of most salmonids worldwide although ontogenetic changes in Salvelinus alpinus weight gain was observed. Kn differed significantly among the populations studied. The strongest effects were related to direct and indirect effects of lake morphometry, while thermal characteristics had mostly indirect effects on Kn. The strength and the sign of the indirect effects of morphometry and temperature were mediated by the direct effects of resource and salmonid densities on Kn.Kn estimates were greater in lakes with shallow basin slopes than those with steep slopes. Shallow basin slopes probably provide habitats that support high prey availability and require lower energy expenditure by salmonids compared to lakes with steep slopes dominated by pelagic habitats. Complementarily, higher winter and summer temperatures favour Kn by supporting higher prey densities and longer periods of feeding activity. Our results may help managers to select lakes that optimise sustainability of salmonid populations based on the joint effects of basin morphometry and the expected thermal modifications induced by global change. [ABSTRACT FROM AUTHOR]

The Arctic charr (Salvelinus alpinus) is a species of cultural, economic and conservation importance, but hitherto, investigations of critical early life stages have been few. Here, at a lake in the United Kingdom, we used swim‐up traps to investigate the phenology of fry emergence and associations between fry density and habitat. The first emergence occurred on 4 or 5 March 2020 and 2021, with numbers peaking and remaining stable in the following 2 weeks. Emergence in 2021 had finished by 27 March but on the same date in 2020 emergence was ongoing when COVID‐19 ended sampling. Substrate particle size ranged 31–94 mm and was negatively correlated with fry density. Likewise, density was negatively correlated with water depth and aquatic plant cover, but there was no relationship with flow velocity. Traps were effective and non‐destructive for assessing the location and productivity of spawning sites for this locally threatened species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

International policy recently adopted commitments to maintain genetic diversity in wild populations to secure their adaptive potential, including metrics to monitor temporal trends in genetic diversity – so‐called indicators. A national programme for assessing trends in genetic diversity was recently initiated in Sweden. Relating to this effort, we systematically assess contemporary genome‐wide temporal trends (40 years) in wild populations using the newly adopted indicators and whole genome sequencing (WGS). We use pooled and individual WGS data from brown trout (Salmo trutta) in eight alpine lakes in protected areas. Observed temporal trends in diversity metrics (nucleotide diversity, Watterson's ϴ and heterozygosity) lie within proposed acceptable threshold values for six of the lakes, but with consistently low values in lakes above the tree line and declines observed in these northern‐most lakes. Local effective population size is low in all lakes, highlighting the importance of continued protection of interconnected systems to allow genetic connectivity for long‐term viability of these populations. Inbreeding (FROH) spans 10%–30% and is mostly represented by ancient (<1 Mb) runs of homozygosity, with observations of little change in mutational load. We also investigate adaptive dynamics over evolutionarily short time frames (a few generations); identifying putative parallel selection across all lakes within a gene pertaining to skin pigmentation as well as candidates of selection unique to specific lakes and lake systems involved in reproduction and immunity. We demonstrate the utility of WGS for systematic monitoring of natural populations, a priority concern if genetic diversity is to be protected. [ABSTRACT FROM AUTHOR]

Lakes in the High Arctic are characterized by their low water temperature, long-term ice cover, low levels of nutrients, and low biodiversity. These conditions mean that minor climatic changes may be of great importance to Arctic freshwater organisms, including fish, by influencing vital life history parameters such as individual growth rates. In this study, Arctic charr sampled from two Svalbard lakes (78–79° N) over the period 1960–2008 provided back-calculated length-at-age information extending over six decades, covering both warm and cold spells. The estimated annual growth in young-of-the-year (YOY) Arctic charr correlated positively with an increasing air temperature in summer. This increase is likely due to the higher water temperature during the ice-free period, and also to some extent, due to the winter air temperature; this is probably due to thinner ice being formed in mild winters and the subsequent earlier ice break-up. However, years with higher snow accumulation correlated with slower growth rates, which may be due to delayed ice break-up and thus a shorter summer growing season. More than 30% of the growth in YOY charr could be explained specifically by air temperature and snow accumulation in the two Arctic charr populations. This indicated that juvenile Svalbard Arctic charr may experience increased growth rates in a future warmer climate, although future increases in precipitation may contradict the positive effects of higher temperatures to some extent. In the longer term, a warmer climate may lead to the complete loss of many glaciers in western Svalbard; therefore, rivers may dry out, thus hindering migration between salt water and fresh water for migratory fish. In the worst-case scenario, the highly valuable and attractive anadromous Arctic charr populations could eventually disappear from the Svalbard lake systems. [ABSTRACT FROM AUTHOR]

This article explores the estimation of fish mortality rates using catch curves and critiques the linear regression method proposed by Ricker (1975). The authors argue that this method is biased and advocate for the use of more recent and accurate methods with age-frequency datasets from various sources. The article emphasizes the importance of appropriate error structures, not transforming count data, and not omitting zero counts or truncating low counts at old age. The authors conclude that log-linear models should be used instead of linear models for catch-curve analyses to obtain more accurate mortality rate estimates. The text also discusses different methods for estimating mortality rates in fisheries research, including the corrected regression coefficient bias (CRCB), Pella-Massey (PM), and generalized beta (GB) methods. The authors recommend abandoning the unweighted linear regression method in favor of these alternative methods and suggest further research to assess the accuracy of mortality estimates obtained from catch-curve analyses. [Extracted from the article]

Arctic char (Salvelinus alpinus) and Dolly Varden (S. malma) are two closely related species in the genus Salvelinus. Both species show substantial intra-specific variation in ecology, morphology, and post-glacial history across their distributional ranges, which has presented substantial challenges for conservation and management and has led to the coining of the term, 'the charr problem'. Arctic char and Dolly Varden have been studied extensively by scientists since the 1700s, not only because these fishes play important ecological roles within ecosystems, but also because they are culturally, economically, and recreationally valuable. While several detailed reviews have been published on Arctic char over the past 40 years, Dolly Varden remain understudied. In addition, advances in the fields of genetics, ecology, and morphometrics have improved our understanding of the behavior, feeding, habitat requirements, post-glacial histories and intraspecific diversity of each of these two species. Herein, we present an updated review that focuses on placing findings from more recently published (through 2022) phylogenetic, ecological and morphometric studies within the foundational context of earlier papers and reviews (since 1943). We also review anticipated effects of climate change on both species. Across their ranges, Arctic char and Dolly Varden can display a variety of life history types, with many populations exhibiting anadromy and/or potadromy; due to their use of distinct habitats at specific life stages, migratory chars are vulnerable to climate-induced changes to habitat quantity and quality. In addition to reviewing the existing literature, we highlight knowledge gaps and research priorities that, when addressed, will enable more informed conservation and management initiatives for these highly valued fishes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Most population genomic tools rely on accurate single nucleotide polymorphism (SNP) calling and filtering to meet their underlying assumptions. However, genomic complexity, resulting from structural variants, paralogous sequences, and repetitive elements, presents significant challenges in assembling contiguous reference genomes. Consequently, short-read resequencing studies can encounter mismapping issues, leading to SNPs that deviate from Mendelian expected patterns of heterozygosity and allelic ratio. In this study, we employed the ngsParalog software to identify such deviant SNPs in whole-genome sequencing (WGS) data with low (1.5×) to intermediate (4.8×) coverage for four species: Arctic Char (Salvelinus alpinus), Lake Whitefish (Coregonus clupeaformis), Atlantic Salmon (Salmo salar), and the American Eel (Anguilla rostrata). The analyses revealed that deviant SNPs accounted for 22% to 62% of all SNPs in salmonid datasets and approximately 11% in the American Eel dataset. These deviant SNPs were particularly concentrated within repetitive elements and genomic regions that had recently undergone rediploidization in salmonids. Additionally, narrow peaks of elevated coverage were ubiquitous along all four reference genomes, encompassed most deviant SNPs, and could be partially associated with transposons and tandem repeats. Including these deviant SNPs in genomic analyses led to highly distorted site frequency spectra, underestimated pairwise FST values, and overestimated nucleotide diversity. Considering the widespread occurrence of deviant SNPs arising from a variety of sources, their important impact in estimating population parameters, and the availability of effective tools to identify them, we propose that excluding deviant SNPs from WGS datasets is required to improve genomic inferences for a wide range of taxa and sequencing depths. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Iteroparity occurs when organisms reproduce more than once, and is seen as a bet-hedging reproductive strategy. Despite a wealth of research on iteroparous Atlantic salmon, steelhead, brown trout, and Arctic charr, the determinants of reproductive investment, the intra- and interspecific differences in the degree of iteroparity, the drivers of repeat spawning, and the contribution of repeat spawners to populations and sustainability remain unclear. In particular, the knowledge base is stronger for Atlantic salmon and brown trout, but relatively weak for Arctic charr and steelhead. While juveniles, maiden spawners and repeat spawners are facing similar challenges, many threats specific to the kelt stage are emerging (e.g., downstream migration passed barriers after spawning). Recent work has quantified the benefits of iteroparity for population resilience, and the potential for iteroparity to increase when anthropogenic stressors are mitigated. This is the first literature review paper synthetizing the growing knowledge base that exists on various aspects of the ecology and biology of repeat spawners in freshwater and at sea, the threats they face, the proximate and ultimate mechanisms underlying iteroparity in salmonids, the importance of iteroparity for population-level processes, as well as highlighting pressing areas of research. Collectively, this work offers a valuable resource to fisheries scientists and managers by shedding light on an important life-history stage that warrants more attention to mitigate these threats and restore healthy wild salmonid populations. [ABSTRACT FROM AUTHOR]

Motives for fishing differ among fishers, which may imply different effects of climate change on the net values of fishing. Climate change has impacts on fish population dynamics and on other factors in the fishers' harvest decision, such as alternative sources of food or income. Here we present a bio-economic model that includes impacts of climate change on fish population and on net values of harvest by fishers with recreational or subsistence fishing motives. The conceptual analysis shows that the economic effects of climate change with simultaneous impacts on fish population growth and harvest values are inconclusive with common fishing access for both fisher types and when there are opposite simultaneous climate effects with exclusive access for one of the fisher types. Numerical results from our model of Arctic char (Salvelinus alpinus) in northern Sweden indicate that climate change, measured as temperature increases, reduces fish population growth but increases net values of fishing for both fisher types. The combined net effect of these counteracting forces is that annual net values can almost cease for the subsistence fisher in the future but increase considerably for the recreational fisher. [ABSTRACT FROM AUTHOR]

Extinctions occur naturally in all environments, but rates have accelerated rapidly during the Anthropocene, especially in fresh water. Despite supporting many fish species of conservation importance, there has never been a formal assessment of their extinction risks in Britain, which has impeded their inclusion in relevant legislation and policy. This study therefore used the International Union for the Conservation of Nature (IUCN) Red List of Threatened Species™ Categories and Criteria to conduct the first systematic assessment of the extinction risks and threats facing the native freshwater and diadromous fishes of Britain. In addition, national assessments were produced for England, Scotland and Wales, reflecting the level at which environmental policy decisions are taken in Britain.Seven species were categorized as being threatened with extinction at the regional level, with European eel Anguilla anguilla and allis shad Alosa alosa classified as Critically Endangered, Atlantic salmon Salmo salar, vendace Coregonus albula and European whitefish Coregonus lavaretus classified as Endangered, and Arctic charr Salvelinus alpinus and twaite shad Alosa fallax classified as Vulnerable. In addition, burbot Lota lota was classified as Regionally Extinct, ferox trout Salmo ferox was categorized as Data Deficient, and 25 species were categorized as Least Concern. European sturgeon Acipenser sturio and houting Coregonus oxyrinchus, although probably native, qualified as only vagrants in fresh water, so were categorized as Not Applicable.The assessments provide objective baselines against which future changes can be determined, and a key evidence base to support policy and management decisions for the conservation of freshwater and diadromous fish species and their habitats in Britain. It is recommended that the assessments are repeated every 10 years, which would enable changes in conservation status, the effectiveness of policies and where targeted interventions may be required to be examined using the Red List Index. [ABSTRACT FROM AUTHOR]

ABSTRACTTeleost 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.

High-latitude aquatic ecosystems are responding to rapid climate warming. A longer ice-free season with higher water temperatures may accelerate somatic growth in lake ectotherms, leading to widespread ecological implications. In fish, rising temperatures are expected to boost rates of food intake and conversion, and predictions based on empirical relationships between temperature and growth suggest a substantial increase in fish growth rates during the last decades. Fish abundance negatively affects growth by limiting food availability. This field study addresses the effects of climate warming on growth of a subarctic population of Arctic charr (Salvelinus alpinus (L.) over nearly 40 years. Juvenile growth of 680 individuals of Arctic charr, was reconstructed by sclerochronological analysis using sagittal otoliths sampled annually from the early 1980s to 2016. Statistical modelling revealed a positive effect of water temperature, and a negative effect of abundance on somatic growth in juvenile individuals. Temperature dependence in growth was significant for average and fast-growing individuals across all investigated age classes. These findings suggest that, as temperatures rise, somatic growth of Arctic charr will increase in high latitude lakes. Climate warming will thus influence cold water fish life history and size-structured interactions, with important consequences for their populations and ecosystems. [ABSTRACT FROM AUTHOR]

Environmental change in the Arctic has impacted the composition and structure of marine food webs. Tracking feeding ecology changes of culturally-valued Arctic char (Salvelinus alpinus) and ringed seals (Pusa hispida) can provide an indication of the ecological significance of climate change in a vulnerable region. We characterized how changes in sea ice conditions, sea surface temperature (SST), and primary productivity affected the feeding ecology of these two keystone species over a 13- and 18-year period, respectively, in northern Labrador, Canada. Arctic char fed consistently on pelagic resources (δ13C) but shifted over time to feeding at a higher trophic level (δ15N) and on more marine/offshore resources (δ34S), which correlated with decreases in chlorophyll a concentration. A reduction in Arctic char condition factor and lipid content was associated with higher trophic position. Ringed seals also shifted to feeding at a higher trophic level, but on more pelagic resources, which was associated with lower SST and higher chlorophyll a concentrations. Years with abnormally high SSTs and reduced sea ice concentrations resulted in large isotopic niche sizes for both species, suggesting abrupt change can result in more variable feeding. Changes in abundance and distribution of species long valued by the Inuit of Labrador could diminish food security. [ABSTRACT FROM AUTHOR]

Alternative migratory tactics in salmonids reflect the large observed interindividual variation in spatial behaviour which may range from strict freshwater residency to uninterrupted anadromy. In Salvelinus, sea migrations are performed during the ice‐free period as freshwater overwintering is thought to be obligatory due to physiological constraints. As a result, individuals can either migrate the next spring or remain in freshwater, as anadromy is generally considered facultative. In Arctic charr (Salvelinus alpinus), skipped migrations are known to occur, but limited data are available regarding their frequencies within and among populations. Here, the authors used an otolith microchemistry approach relying on strontium (88Sr) to infer movements between freshwater and marine habitats, and annual oscillations in zinc (64Zn) to help with age identification. They determined the age‐at‐first‐migration and the occurrence of subsequent annual migrations in two Nunavik Arctic charr populations sampled in Deception Bay (Salluit) and river systems linked to Hopes Advance Bay (Aupaluk), northern Québec, Canada. The mode for age‐at‐first‐migration was 4+ for both populations, although it exhibited large variation (range: 0+ to 8+). Skipped migrations constituted a rare event, as 97.7% and 95.6% of the examined Arctic charr at Salluit (n = 43, mean age = 10.3 ± 2.0 years) and Aupaluk (n = 45, mean age = 6.0 ± 1.9 years), respectively, were found to have performed uninterrupted annual migrations after initiation of the behaviour. The consistency of the annual migrations suggests that the tactic is sufficiently fitness rewarding to be maintained under current environmental conditions. From a fisheries management perspective, these repeated migrations combined with low site fidelity in this species may lead to large interannual variations in abundance at the local scale, which may represent a challenge for monitoring Arctic charr demographics on a river‐by‐river basis. [ABSTRACT FROM AUTHOR]

During summer, native anadromous Arctic char (Salvelinus alpinus) and the alien species pink salmon (Oncorhynchus gorbuscha) now coexist in marine environments in Svalbard, following the introduction of the latter in the Barents Region. To investigate potential dietary competition between these two salmonid species, stomach contents from Arctic char (n = 301) and pink salmon (n = 28) were sampled from different areas within the archipelago. The most important prey in terms of biomass for both salmonid species were amphipods; Themisto libellula (B = 26.0%) for Arctic char and Onisimus litoralis (B = 35.0%) for pink salmon. Pianka's niche overlap revealed that dietary overlap between the two species was moderately high (Oobs = 0.59); both species had strong associations with intertidal invertebrates in areas where direct comparisons were possible (Kongsfjorden/Krossfjorden). However, both salmonid species did also eat some fish, with Arctic char consuming more offshore pelagic fish, while the small number of fish eaten by pink salmon were primarily coastal demersal fish species. Arctic char was a more generalist feeder, while pink salmon was more of a dietary specialist. Furthermore, the diet composition of the Arctic char consisted of 32.9% Atlantic prey while the pink salmon, surprisingly, ate only Arctic species, likely due to their tightly coastal feeding habits. Even though the sample size for pink salmon was low, this study contributes new insights into salmonid diets in Svalbard and the potential for introduced species to compete with native Arctic endemics, particularly in the expected warmer Arctic of the future. [ABSTRACT FROM AUTHOR]

This ethnographic study explores and compares the relationships that locals in Rossfjord, North Norway, have to the oystercatcher and the sea-going Arctic char respectively. Both these animals are highly valued locally, while the valuations at first look very different. The oystercatcher is protected by building bin-cases for its nesting, while the Arctic char is killed and eaten. Discussing these valuations against the value theory of David Graeber, I argue that they both connect to an underlying perception of the freedom and autonomy of wild animals, where what is not fully understood enhances an experience of wonder and appreciation of what I call the wild. [ABSTRACT FROM AUTHOR]

Background: Substantial variation in male fertility is regularly observed in farmed Arctic charr. However, detailed investigations of its fluctuation during a reproductive season and across years are lacking. Furthermore, information about the effect of underlying genetic factors influencing sperm quality is scarce. The current study focused on seasonal and age-related factors that may affect sperm quality characteristics in males reared in natural and delayed photoperiods. Animals were sampled three times for two consecutive years, and sperm quality parameters were recorded using a computer-assisted sperm analysis (CASA) system. Thereafter, high-throughput sequencing technologies were applied, aiming to identify genomic regions related to the variation of sperm quality throughout the reproductive season. Results: An across-season variation in the recorded sperm quality parameters was evident. Overall, 29% and 42% of males from the natural and delayed spawning groups had a highly variable total progressive motility. Males at four years of age showed significantly higher sperm motility and velocities during the early October and November recordings compared to the following year when the same animals were five years of age. On the other hand, the opposite was observed regarding sperm concentration during the last sampling. A genome-wide FST scan detected SNP differentiation among males with high and low variability in total progressive motility (PM) on eight chromosomes (FST > 0.17), Genome wide windows with the highest FST contained SNPs in proximity (within 250 kb up- and downstream distance) to 16 genes with sperm quality biological functions in mammalian species. Conclusion: Our findings provide a detailed view of seasonal, age-related, and genetic effects on sperm quality and can be used to guide decisions on broodstock selection and hatchery management. [ABSTRACT FROM AUTHOR]

Adaptive evolution may be influenced by canalization, the buffering of developmental processes from environmental and genetic perturbations, but how this occurs is poorly understood. Here, we explore how gene expression variability evolves in diverging and hybridizing populations, by focusing on the Arctic charr (Salvelinus alpinus) of Thingvallavatn, a classic case of divergence between feeding habitats. We report distinct profiles of gene expression variance for both coding RNAs and microRNAs between the offspring of two contrasting morphs (benthic/limnetic) and their hybrids reared in common conditions and sampled at two key points of cranial development. Gene expression variance in the hybrids is substantially affected by maternal effects, and many genes show biased expression variance toward the limnetic morph. This suggests that canalization, as inferred by gene expression variance, can rapidly diverge in sympatry through multiple gene pathways, which are associated with dominance patterns possibly biasing evolutionary trajectories and mitigating the effects of hybridization on adaptive evolution. Transcriptomic analyses in the offspring of Arctic charr morphs (Salvelinus alpinus) and their hybrids at two stages of cranial development suggest that gene expression variance can rapidly diverge in sympatry and is conditioned by dominance patterns. [ABSTRACT FROM AUTHOR]

The highly polymorphic taxon European brown trout (genus Salmo) has high phenotypic plasticity, displaying a complex pattern of morphological and life-history variation, contributing to taxonomic confusion. Three main mitochondrial lineages (Adriatic, Mediterranean, and marmoratus) developed during the Pleistocene climatic events in the southern Alpine ecosystem. Here, the natural distribution of native brown trout S. trutta is controversial, complicated by introductions of the Atlantic strain. By investigating museum vouchers, this study aimed to retrace the historical presence of brown trout in the southern Alpine ecosystem before the beginning of mass introductions, which occurred since the middle of the 19th century. By examining the combination of historical and current genetic variability, this study aims to depict the actual impact of introductions of the introduced strain, increasing knowledge and informing conservation strategies and future management plans. The molecular approaches selected were: (i) sequencing of the mitochondrial control region and (ii) genotyping of the nuclear gene LDH-C1*. Vouchers dated the presence of the native Adriatic strain since 1821, while current genetic variability showed the widespread signature of introgression, a consequence of several decades of introductions. Focused plans to preserve local lineages are urgently needed, including short-term solution to avoid complete pauperization of this ecosystem. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Polymorphic species are useful models for investigating the evolutionary processes driving diversification. Such processes include colonization history as well as contemporary selection, gene flow, and genetic drift, which can vary between intraspecific morphs as a function of their distinct life histories. The interactive and relative influence of such evolutionary processes on morph differentiation critically informs morph‐specific management decisions and our understanding of incipient speciation. We therefore investigated how geographic distance, environmental conditions, and colonization history interacted with morph migratory capacity in the highly polymorphic fish species, Arctic Charr (Salvelinus alpinus). Using an 87 k SNP chip we genetically characterized recently evolved anadromous, resident, and landlocked charr collected from 45 locations across a secondary contact zone of three charr glacial lineages in eastern Canada. A strong pattern of isolation by distance across all populations suggested geographic distance principally shaped genetic structure. Landlocked populations had lower genetic diversities and higher genetic differentiation than anadromous populations. However, effective population size was generally temporally stable in landlocked populations in comparison to anadromous populations. Genetic diversity positively correlated with latitude, potentially indicating southern anadromous populations' vulnerability to climate change and greater introgression between the Arctic and Atlantic glacial lineages in northern Labrador. Local adaptation was suggested by the observation of several environmental variables strongly associating with functionally relevant outlier genes including a region on chromosome AC21 potentially associated with anadromy. Our results demonstrate that gene flow, colonization history, and local adaptation uniquely interact to influence the genetic variation and evolutionary trajectory of populations. [ABSTRACT FROM AUTHOR]

Arctic char (Salvelinus alpinus) is a top predator and the most widespread fish in Arctic lakes. The presence of Arctic char affects the predator–prey dynamics of the key species in the food webs in these lakes. This study sought to elucidate the effects of habitat (littoral, pelagic, or profundal) and lake morphometry on the trophic position of this char in the food web. Using stomach content and stable isotope analyses, we investigated the effect of fish length, habitat, and time (individual survey years: 2008, 2013, 2018, and 2019) on the dietary niches of landlocked Arctic char populations during summer in two west Greenland lakes: Badesø (area 0.8 km2, mean depth 9.2 m) and Langesø (area 0.3 km2, mean depth 5.0 m). The small char (<20 cm fork length) in Badesø generally foraged less littoral macroinvertebrates than those from Langesø. The large chars were mainly piscivorous in both lakes. In Badesø, there was a shift from relying on littoral to pelagic invertebrates by the small char from 2008–2013 to 2018–2019. The proportionally larger size of the littoral habitat in the smaller Langesø led to an increased reliance on littoral-derived macroinvertebrates in the diet of the small char, more so than in the larger Badesø, where the predominant reliance was on pelagic sources. [ABSTRACT FROM AUTHOR]

Objective: The broad objective of our study was to use a histological approach to examine possible tissue‐level effects of exposure to elevated CO2 in freshwater young‐of‐year salmonids. Methods: To study these effects, young‐of‐year Arctic Char Salvelinus alpinus, Rainbow Trout Oncorhynchus mykiss, and Brook Trout S. fontinalis were exposed to either control levels of CO2 (1400 μatm) or elevated levels of CO2 (5236 μatm) for 15 days. Fish were then sampled for gill, liver, and heart tissues and histologically analyzed. Result: A species effect was observed for the length of secondary lamellae, as Arctic Char had significantly shorter secondary lamellae than the other species. No notable changes within the gills and livers of Arctic Char, Brook Trout, or Rainbow Trout exposed to elevated CO2 were observed. Conclusion: Generally, our results indicated that elevated CO2 levels over 15 days do not induce catastrophic tissue damage and it is unlikely that fish health would be seriously impacted. Ongoing research dedicated to examining how elevated CO2 long‐term may affect internal tissues of fish will allow for a more comprehensive understanding of how fish may fair with ongoing climate change and in aquaculture facilities. [ABSTRACT FROM AUTHOR]

Brown trout (Salmo trutta L. 1758) and Arctic charr [Salvelinus alpinus (L. 1758)] tagged with acoustic transmitters migrated from fresh water to the sea mainly in May and June, but with large individual variation in migration timing. For S. trutta, large individuals (42–86 cm total length) migrated earlier in the season than small individuals (18–27 cm). For S. alpinus, no such pattern was found, likely because of the small size range of tagged fish (28–41 cm). S. trutta stayed longer at sea than S. alpinus (average 2 vs. 1 month). Early migrants of S. trutta stayed for a shorter period at sea than late migrants, whereas no such pattern was observed for S. alpinus. Large S. trutta moved quickly away from the river and spent average 3 days to reach a receiver line 20 km from the river mouth, whereas small S. trutta and S. alpinus migrating that far spent 2–3 weeks on the same distance. S. trutta utilized the entire fjord system and had a greater proportion of long‐distance migrants (>20 km, 78% and 59% of large and small S. trutta, respectively) than S. alpinus (29%). S. alpinus mostly stayed in the inner fjord areas, and none were recorded in the outermost part of the fjord. The difference in the use of marine areas may be caused by variation in prey choice and spatial distribution of the preferred prey groups. Stable isotope analysis showed that S. trutta had been feeding at a higher trophic level than S. alpinus. S. trutta had mainly fed on marine fish and shrimps, whereas S. alpinus had large proportions of freshwater invertebrates in the diet, suggesting that the estuary with benthos and amphipods drifting from the river was an important feeding habitat for S. alpinus. In conclusion, major differences in habitat use, migration patterns and feeding strategies were found between sympatric anadromous S. trutta and S. alpinus while at sea. [ABSTRACT FROM AUTHOR]

Rapid climate change occurring in the Arctic may affect the diet of ecologically and culturally important northern fish species. Here, a systematic literature review was completed for eight fish species found across the North American Arctic, with a focus on Inuit Nunangat, to identify major prey items, summarize feeding strategies, and highlight data gaps. Arctic Char (Salvelinus alpinus), Dolly Varden Char (Salvelinus malma), Lake Trout (Salvelinus namaycush), Bull Trout (Salvelinus confluentus), Inconnu (Stenodus leucichthys), Lake Whitefish (Coregonus clupeaformis), Broad Whitefish (Coregonus nasus), and Burbot (Lota lota), were selected as species of interest due to their ecological and cultural importance. The 74 studies reviewed indicate that these species are generalist feeders that demonstrate wide dietary niches, as well as the tendency to avoid agonistic interactions by partitioning resources when they co-occur with an overlapping species. Across coastal, lacustrine, and riverine systems, the most commonly consumed prey items are insects (Diptera spp.), as well as benthic forage fishes such as sculpins (Family: Cottidae). Insects are major prey items in riverine systems, where diets appear to be more generalized, compared to lakes. Anadromous species in coastal waters most commonly feed on various crustaceans and forage fishes. Benthic forage fishes, insects, zooplankton, and mollusks are widely consumed prey items in Arctic lakes. Burbot, Inconnu, and resident Dolly Varden had the most specialized feeding strategies, due in part to their habitat requirements and morphology, while Lake Trout and resident Arctic Char often form multiple ecotypes in lakes, some with different feeding behaviors. Knowledge gaps regarding northern fish trophic ecology are highlighted, and in particular include riverine systems and winter foraging behavior. This review is intended to inform predictions regarding the impacts of climate change on fish tropic ecology and to guide future research. [ABSTRACT FROM AUTHOR]

Salmon‐lice have the potential to change the behaviour and growth of their salmonid host species. Here, the baseline infection levels of salmon‐lice of post‐smolts (n = 815) and veteran migrants (n = 875) of sea‐run Arctic charr (Salvelinus alpinus Linnaeus, 1758) were monitored over two successive years in a sub‐Arctic Norwegian fjord without farming of salmonids. All Arctic charr were collected after the sea‐migration period from a trap placed in the river, ascending to their overwintering freshwater habitat (Lake Laksvatn). The sea‐lice infection showed a stable infection across the 2 years while increasing through the migration period and with the size of the wild sea‐run Arctic charr. The prevalence of sea‐lice infection was intermediate to high, and the intensities of sea‐lice infections observed were generally modest, although some individuals had high infections. The relatively high infection of salmon‐lice highlights the potential detrimental effects these parasites can have at both the individual and population level of such endangered sub‐Arctic life‐history strategies. A comparative study should be performed in fjords with aquaculture activity as focal points for salmon‐lice, to investigate the impact farming have on sea‐run Arctic charr populations. [ABSTRACT FROM AUTHOR]

Personality is now recognized as an ecologically and evolutionarily significant phenomenon because it can affect fitness directly. However, empirical studies specifically tackling the importance of personality in the processes of adaptive divergence and speciation are scarce. Whether selection favours plasticity or canalization of personality traits in specific contexts and how ecological conditions affect the presence and the structure of personalities remain to be elucidated. We used five populations of Arctic charr, Salvelinus alpinus , chosen along a gradient of genetic and phenotypic divergence: an anadromous population supposedly close to the ancestral population and two pairs of sympatric lake morphs. Fish were raised individually from eggs in a common garden experiment to specifically assess the genetic bases of the boldness trait in these populations. Thirty-two individuals per morph were repeatedly tested at 11 months old in an open field test with a shelter to assess boldness. The repeatability of the boldness trait (i.e. personality), within- and among-individual variation and temporal variation were assessed within each population. Then, the temporal plasticity in boldness and boldness mean score were assessed among populations. The results show differences between populations for the three variables, with the highest repeatability in the most diverged population, an increase in boldness over time and a lower mean value (especially the first time they were exposed to the novel environment) in the anadromous population. This suggests that boldness and temporal plasticity differ between the anadromous population and the more diverged lake populations under a controlled embryonic/juvenile environment. Further research is needed to verify the contribution of temporal plasticity for personality traits in the context of rapid adaptive radiation such as that seen in Arctic charr. • Boldness and related parameters were measured in five populations of Arctic charr. • Temporal variation in boldness was assessed by repeated measures. • Lower boldness and higher temporal plasticity are shown in the ancestral population. • Contribution of temporal plasticity in adaptive radiation remains to be elucidated. [ABSTRACT FROM AUTHOR]

Our ability to rapidly monitor species is essential for effective resource management and for establishing conservation practices. Current monitoring practices for many fish species are not effective across multiple habitats due to limited resources, permit restrictions, etc. In response, environmental DNA (eDNA)‐based surveying and monitoring programmes are increasingly being developed and applied to meet the growing demands of local regulators and resource managers. The management of Arctic char (Salvelinus alpinus), a fish species of economical and societal importance, is a prime candidate for eDNA surveillance as many existing and endemic populations are increasingly threatened by human activity and climate change.Here we applied and tested the effectiveness of using eDNA to survey endemic and transplanted Arctic char populations across north Wales, which represents the southern extent of the Arctic char geographic range. We used a species‐specific quantitative polymerase chain reaction (qPCR) method to assess Arctic char occurrence and estimated the biomass (e.g., abundance) of Arctic char populations for each of the sampled lakes.We found Arctic char present in four of the five lakes with eDNA detection increasing with increasing lake depth. Spatial distribution of Arctic char eDNA detection was not found to be related to spatial location or distance from inlet or outlet for each sampled lake. Arctic char biomass was estimated from eDNA using a range of previously documented eDNA concentrations to biomass measures. Following biomass validation from one lake, we suggested that a mid‐range measure of eDNA to biomass estimate (from the currently available literature) is most likely, resulting in a range of 3,002–42,614 g/ha for our biomass estimates across all sites.Environmental DNA sampling is an effective method for assessing Arctic char populations and offers an informative base for estimating population densities. DNA detection was not spatially structured, which might indicate that the transport dynamics of eDNA are more unpredictable than previously anticipated and that standard sampling strategies should employ spatial sampling in their design to ensure adequate detection is obtained from eDNA collection efforts.With the increasing infeasibility of traditional sampling and surveying methods it is essential to continue to test and refine our eDNA capabilities. These findings highlight the usability and sampling design strategy needed for eDNA based surveying of known and unknown locations for endemic species. We also provide an initial cross‐study framework for estimating fish abundances from eDNA data that uses and builds on existing knowledge and trends in contrast to study or site‐specific assessments. [ABSTRACT FROM AUTHOR]

Arctic charr (Salvelinus alpinus [L.] complex) has been widely used as a model system for studies in evolutionary ecology because of its diversity in feeding ecology, habitat use, life history forms, and associated morphologies observed in matured individuals. However, we still know relatively little about traits exhibited early in life of the species, although the trait diversity of matured individuals may largely be shaped during development. Egg size is a key determinant of various traits exhibited early in life. Therefore, describing egg size variation within- and between-individuals as well as the link between egg size and adult traits will be a useful step in understanding the early life trait diversity of Arctic charr. Here, using Greenlandic Arctic charr, which includes alternative life history forms (i.e. anadromous and resident) and spawning habitat use (i.e. lake and river spawner), we described egg size variation (i.e. clutch-mean egg diameter and within-clutch variation) and explored the link between egg size variation and female body length, life history form, and spawning habitats. As in many other fishes, clutch-mean egg diameter increased with female body length. No significant effect of other female traits on clutch mean-egg diameter was detected, suggesting that female body size variation could be a direct cause of early life history trait variation. On the other hand, we found that the degree of within-clutch variation of the anadromous life history form was higher than that of the resident life history form. The pattern could be interpreted in an adaptive context. For instance, given that the anadromous life history form tends to be semelparous, anadromous females could decrease the likelihood of complete reproductive failure by producing variable-sized offspring within a clutch since at least some offspring are expected to be matched to the prevailing environment. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity, the ability of an organism to express multiple phenotypes in response to the prevailing environmental conditions without genetic change, may result in a response to anthropogenic environmental change. Given that increasing climate variability is predicted to pose a greater risk than directional climate change, we tested the effect of a water temperature differential of 4 °C on the Arctic charr phenotypic within a single generation. We demonstrate that Arctic charr phenotype can respond rapidly and markedly to an environmental temperature cue. The plastic response to different temperature regimes comprised a shift in the mean expressed phenotype but also coupled with a reduction in the between-individual phenotypic variation in the expressed head shape. The magnitude of shape difference between temperature conditions was cumulative over time but the rate of divergence diminished as fish became larger. Overall, individuals raised in the elevated temperature treatment expressed a phenotype analogous to a benthivorous ecotype of this species, rather than that of the parental pelagic feeding form. The response of cold-water freshwater species to temperature change is likely to be an interaction between the capacity of the organism for phenotypic plasticity, the mean speed of change in the environment, and the degree of short interval variation in the environment. [ABSTRACT FROM AUTHOR]

In the region of King William Island, Nunavut, in the Canadian high Arctic, populations of salmonids including Arctic char (Salvelinus alpinus), cisco (Coregonus autumnalis and C. sardinella) as well as lake whitefish (C. clupeaformis) are diadromous, overwintering in freshwater and transitioning to saline waters following ice melt. Since these fish were sampled at the same time and from the same traditional fishing sites, comparison of their skin structures, as revealed by 16S rRNA gene sequencing, has allowed an assessment of influences on wild fish bacterial communities. Arctic char skin microbiota underwent turnover in different seasonal habitats, but these striking differences in dispersion and diversity metrics, as well as prominent taxa involving primarily Proteobacteria and Firmicutes, were less apparent in the sympatric salmonids. Not only do these results refute the hypothesis that skin communities, for the most part, reflect water microbiota, but they also indicate that differential recruitment of bacteria is influenced by the host genome and physiology. In comparison to the well-adapted Arctic char, lake whitefish at the northern edge of their range may be particularly vulnerable, and we suggest the use of skin microbiomes as a supplemental tool to monitor a sustainable Indigenous salmonid harvest during this period of change in the high Arctic. [ABSTRACT FROM AUTHOR]

Climate change can affect fish species directly (e.g. through physiological stress) or indirectly (e.g. species interactions). Whether individual species will experience net benefits or net losses is important to understand from a fisheries management perspective. Ireland has a unique freshwater fish community that faces considerable uncertainty in relation to the impact of climate change. Vulnerability of fish species and subspecies (n = 32) in Ireland were investigated through an expert‐based questionnaire and a trait‐based assessment. Fish species were assessed based on exposure, sensitivity and adaptive capacity. The expert‐based questionnaire predicted that one species, Arctic char Salvelinus alpinus was assigned the rank of high vulnerability, seven species were assigned moderate to high vulnerability, twenty species were assigned moderate vulnerability, and four species were of low to moderate vulnerability. Life‐history characteristics of the fish species were analysed to identify traits characteristic of vulnerable fish species (e.g. Vulnerability to fishing and Trophic level). Coldwater species are highly vulnerable, with indirect effects through interactions with other species or in combination with non‐climatic stressors (e.g. water quality & barriers to migration) being a significant concern. The results provide a vulnerability ranking for Ireland's freshwater fish, that can be utilised by fisheries managers and allows for prioritising of an often‐limited conservation resource. [ABSTRACT FROM AUTHOR]

[Display omitted] • The causative agent of proliferative kidney disease (PKD) is Tetracapsuloides bryosalmonae. • Tetracapsuloides bryosalmonae is not a recently introduced parasite in Iceland. • However, PKD is an emerging disease in wild Icelandic salmonids. • Tetracapsuloides bryosalmonae has increased its distribution in Icelandic lakes over the last two decades. • The impact of PKD will increase with further global temperature increases. Tetracapsuloides bryosalmonae is a myxozoan parasite and the causative agent of proliferative kidney disease (PKD), a serious, temperature-dependent and emerging disease affecting salmonid fish. It was first identified in Iceland in 2008, from Arctic charr inhabiting a shallow lowland lake. The aim of this study was to investigate the distribution and prevalence of macroscopic and subclinical T. bryosalmonae infections in Icelandic salmonids and compare different time periods, in context with depths, volumes, altitudes and areas of the lakes and fish age. Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) from 34 lakes, sampled between 1994–1998 and 2009–2017, were examined for macroscopic signs of PKD (n = 2,151) and the presence of T. bryosalmonae infections (n = 1,424). In the earlier period, 43% of lakes (10/23) harboured T. bryosalmonae -infected fish. The mean prevalence in those lakes was 62.1%, being most common in shallow lowland lakes whilst deeper lakes at high altitudes were all free from infection. Only a single fish from one lake showed macroscopic signs of PKD, a shallow lowland lake in southwestern Iceland. In the latter period, T. bryosalmonae was found in 16/18 lakes studied (89%), with a mean prevalence of 78–79% (excluding T.b. free lakes), being most common in the smaller, shallower lakes at lower alttudes. Macroscopic signs of PKD were observed in 11 of 18 of the lakes studied (61%) with prevalences up to 67%, most common in younger fish inhabiting small shallow lowland lakes. The results indicate that the distribution of T. bryosalmonae and the presence of PKD in Iceland have increased over the last few decades. The disease was almost non-existent in the 1990s but has become very common during the last decade or two. With further water temperature increases, as predicted by climate models, PKD is likely to increasingly affect wild salmonid populations in Iceland. [ABSTRACT FROM AUTHOR]