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Studies to determine precision and bias of both methods and age-readers are important to evaluate reliability of age data used for developing fisheries management objectives. We assessed within-reader, between-reader, and between-method precision (coefficient of variation, CV%) and bias of age estimations for long-lived lake trout, Salvelinus namaycush, from Great Bear Lake using three readers with different levels of experience. The assessment used independent age estimates (n = 3 per reader) from whole and transverse-sectioned otoliths (range = 1–67 years), and pelvic fin-ray sections (range = 3–26 years). We also examined between-method differences in assigned confidence scores. Within readers, age estimates from sectioned otoliths were more precise (2.6–3.0%) than whole (3.6–4.5%) otoliths. Between whole and sectioned otoliths, precision of age estimates was 5.4% and bias was low up to age 20. Age was typically under-estimated from whole otoliths compared to sections for fish ≥ 34 years. Increased reader confidence was correlated with greater precision and younger age estimates, particularly for whole otoliths, but less so for fin rays. Age was estimated with higher confidence from otolith sections than other methods. The least experienced reader estimated age with the lowest precision, and between-reader bias was evident among older ages. Age was consistently under-estimated and less precise from pelvic fins compared to sectioned otoliths, and are therefore an unsuitable non-lethal alternative. Sectioned otoliths revealed longevity was greater (67 years) than historically documented using whole otoliths (53 years) for these fish. Our findings contribute to those relying on otoliths or pelvic fin rays to estimate ages of long-lived lake trout populations, which are a key component of freshwater fauna in polar North America.

Populations of northern Dolly Varden (Salvelinus malma malma) exhibit partial seaward migration, yet little is known about this phenomenon in Dolly Varden populations. Our study analyzed data from three different Dolly Varden populations in the western Canadian Arctic in order to determine if: (1) differences in size-at-first seaward migration exist between fish that migrate at early and late ages among populations inhabiting different river systems, and (2) annual growth influences anadromous or resident life history choice. Otolith strontium analysis and back-calculation were used to determine age- and size-at-first seaward migration, respectively. Differences in age- and size-at-first seaward migration were determined across river system and migration age. Back-calculated fish lengths were compared using a mixed effect model to determine how early growth influences migratory tactics (early or late aged smolt, or resident). Our results indicate that fish exhibiting faster early growth migrated in earlier years and at smaller sizes than slower growing fish, however size- and age-at first seaward migration varied by river system. Faster growing Dolly Varden tended to become either residents or early smolts, while slower growth was associated with smolting later in life. This is contrary to life history theory where the fastest growing fish in a population should mature as a resident. Our results indicate factors other than growth may be influencing life history ‘decisions’ in Dolly Varden. Future work on growth efficiencies and metabolic rates is needed to assess how they affect migratory behaviours.

In a polyphenic species, differences in resource use are expected among ecotypes, and homogeneity in resource use is expected within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether specialization of trophic resources by individuals occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within this lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large‐sized individuals and other piscivore individuals. We demonstrated that individual trophic specialization can occur within an ecotype inhabiting a geologically young system (8,000–10,000 yr BP), a lake that sustains high levels of phenotypic diversity of lake trout overall. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes., A common assumption in polyphenism is that partitioning and variability of resource use will occur predominantly among ecotypes rather than within ecotypes. In contrast, homogeneity of resource use is anticipated to occur within ecotypes, be spatially and temporally stable, and provide the selection opportunity for specialization. However, this study provided evidence that variation occurred within an ecotype due to diet specialization among individuals, possibly a precursor to further population diversification via fine‐scale ecological selection.

Arctic ecosystems are changing rapidly due to global warming, industrial development, and economic growth. However, the ecological consequences for these ecosystems are difficult to predict due to limited knowledge on species abundance, distribution, and biodiversity patterns. This study evaluated the diversity and assemblage composition of epibenthic macrofauna in shallow coastal areas from five Eastern Arctic locations with increasing economic and shipping activity. Benthic trawls (n=198) were conducted in nearshore coastal habitats of Anaktalak Bay (Labrador), Churchill (Manitoba), Deception Bay (Quebec), Iqaluit (Nunavut), and Milne Inlet (Nunavut), at depths between 3 and 30 m. Diversity and assemblage composition were compared at various taxonomic levels from phylum to species and correlations with broad oceanographic variables were investigated to identify potential drivers of biodiversity. The spatial variability of benthic assemblages was also assessed within each study location. A total of 297,417 macroinvertebrates was identified, belonging to 900 taxa. Abundance and taxonomic richness were highest in Anaktalak Bay. Shannon-Wiener diversity was higher in Anaktalak Bay, Iqaluit, and Milne Inlet than in Churchill and Deception Bay. Churchill showed the lowest diversity metrics among locations. No relationships were observed between diversity and depth, chlorophyll-a, particulate organic carbon, sea surface temperature, or sea ice duration. Assemblages differed among locations at all taxonomic levels, with the highest dissimilarities at the species level; however, dispersion of samples within-groups was significant, suggesting that factors other than locations (e.g., habitat type) influence assemblage composition. While Churchill, Deception Bay, and Iqaluit showed distinct local spatial patterns in diversity metrics and assemblage composition, no patterns were detected in Anaktalak Bay and Milne Inlet. This study represents one of the largest systematic assessments of coastal epibenthic biodiversity in the Canadian Arctic. It identifies patterns of biodiversity and assemblage composition and provides a baseline for studies of community change and the development of informed management and conservation strategies for Arctic coastal ecosystems.

Spatial and temporal trends of marine harmful algal events in Canada over the last three decades were examined using data from the Harmful Algal Event Database (HAEDAT). This database contains the most complete record of algal blooms, phycotoxins and shellfish harvesting area closures in Canada since 1987. This 30-year review of 593 Canadian HAEDAT records from 1988 to 2017, together with other Canadian data and publications, shows that recurring harmful algal events have been widespread throughout both the Atlantic and Pacific coastal regions. The 367 paralytic shellfish toxin (PST) reports revealed annual and frequent recurrence throughout both the Atlantic and Pacific regions, including multi-year PST events in the Bay of Fundy, the Estuary and Gulf of St. Lawrence and the Strait of Georgia. The 70 amnesic shellfish toxin (AST) records revealed no recognizable trend, as these events were usually area specific and did not recur annually. The increasing frequency of diarrhetic shellfish toxin (DST) events over the period of this review, in total 59 records, can be at least partially explained by increased sampling effort. Marine species mortalities caused by harmful algae (including diatoms, dictyochophytes, dinoflagellates, and raphidophytes), were a common occurrence in the Pacific region (87 reports), but have been reported much less frequently in the Atlantic region (10 reports). Notable Canadian records contained in HAEDAT include the first detection worldwide of amnesic shellfish poisoning (ASP), attributed to the production of domoic acid (an AST) by a diatom (Pseudo-nitzschia multiseries) in Prince Edward Island in 1987. The first proven case of diarrhetic shellfish poisoning (DSP) in Canada and North America was recorded in 1990, and the first closures of shellfish harvesting due to DST (associated with the presence of Dinophysis norvegica) occurred in Nova Scotia in 1992, followed by closures in Newfoundland and Labrador in 1993. In 2008, mass mortalities of fishes, birds and mammals in the St. Lawrence Estuary were caused by Alexandrium catenella and high levels of PST. During 2015, the Pacific coast experienced a large algal bloom that extended from California to Alaska. It resulted in the closure of several shellfish harvesting areas in British Columbia due to AST, produced by Pseudo-nitzschia australis. Data from the Canadian Arctic coast is not included in HAEDAT. However, because of the emerging importance of climate change and increased vessel traffic in the Arctic, information on the occurrence of harmful algal species (pelagic and sympagic = sea ice-associated) in that region was compiled from relevant literature and data. The results suggest that these taxa may be more widespread than previously thought in the Canadian Arctic. Information in HAEDAT was not always robust or complete enough to provide conclusions about temporal trends. Compilation of spatial and temporal information from HAEDAT and other records is nevertheless important for evaluating the potential role of harmful algae as a stressor on Canadian marine ecosystems, and will support the next step: developing a knowledge gap analysis that will establish research priorities for determining their consequences on human and ecosystem health.

Large‐scale biomonitoring of Arctic coastal marine communities is essential to track temporal changes in ecosystems. Despite the potential of environmental DNA (eDNA) as an innovative coastal biomonitoring tool, important questions remain pertaining to its temporal and spatial variation and how this may affect the evaluation of ecosystem changes over time in hydrodynamic ecosystems. In this study, we used eDNA metabarcoding of coastal water samples in two Canadian Arctic ports to evaluate the potential of eDNA to detect temporal transition in marine coastal communities. We sequenced eDNA from approximately 20 surface water samples collected each month (N ≈ 150 samples) covering the transition period between summer and late fall using four different universal primer pairs (two pairs of COI mitochondrial genes and two pairs of 18S rRNA genes). Our results from both primer pairs highlighted a significant transition from the summer to the fall marine community. We also observed a putative link between eDNA peaks of read abundance and timing for different life stages (e.g., spawning and larvae) of several species with the most abundant sequence reads. As such, our results show that temporal variation must be considered in ensuring comprehensive coastal biomonitoring with eDNA. Although much remains to be investigated about the ecology of eDNA, our results contribute to fundamental knowledge on the origin of eDNA and highlight the importance of considering temporal variation in developing guidance for coastal biomonitoring with this approach.

The risk of aquatic invasions in the Arctic is expected to increase with climate warming, greater shipping activity and resource exploitation in the region. Planktonic and benthic marine aquatic invasive species (AIS) with the greatest potential for invasion and impact in the Canadian Arctic were identified and the 23 riskiest species were modelled to predict their potential spatial distributions at pan‐Arctic and global scales. Modelling was conducted under present environmental conditions and two intermediate future (2050 and 2100) global warming scenarios. Invasion hotspots—regions of the Arctic where habitat is predicted to be suitable for a high number of potential AIS—were located in Hudson Bay, Northern Grand Banks/Labrador, Chukchi/Eastern Bering seas and Barents/White seas, suggesting that these regions could be more vulnerable to invasions. Globally, both benthic and planktonic organisms showed a future poleward shift in suitable habitat. At a pan‐Arctic scale, all organisms showed suitable habitat gains under future conditions. However, at the global scale, habitat loss was predicted in more tropical regions for some taxa, particularly most planktonic species. Results from the present study can help prioritize management efforts in the face of climate change in the Arctic marine ecosystem. Moreover, this particular approach provides information to identify present and future high‐risk areas for AIS in response to global warming., Marine aquatic invasive species with the greatest potential for invasion and impact in the Canadian Arctic were identified and modelled to predict their potential spatial distributions at pan‐Arctic and global scales. Modelling for 23 species was conducted under present environmental conditions and two future (2050 and 2100) global warming scenarios. Potential invasion hotspots were identified for Hudson Bay, Northern Grand Banks/Labrador, Chukchi/Eastern Bering seas and Barents/White seas, suggesting that these regions are most vulnerable to invasions. Organisms showed future poleward shifts and overall gains in habitat suitability under future conditions, although some species distributions will likely recede towards the equator.

Fatty acids are well-established biomarkers used to characterize trophic ecology, food-web linkages, and the ecological niche of many different taxa. Most often, fatty acids that are examined include only those previously identified as “dietary” or “extended dietary” biomarkers. Fatty acids considered as nondietary biomarkers, however, represent numerous fatty acids that can be extracted. Some studies may include nondietary fatty acids (i.e., combined with dietary fatty acids), but do not specifically assess them, whereas in other studies, these data are discarded. In this study, we explored whether nondietary biomarker fatty acids can provide worthwhile information by assessing their ability to discriminate intraspecific diversity within and between lakes. Nondietary fatty acids used as biomarkers delineated variation among regions, among locations within a lake, and among ecotypes within a species. Physiological differences that arise from differences in energy processing can be adaptive and linked to habitat use by a species’ ecotype and likely explains why nondietary fatty acid biomarkers can be a relevant tool to delineate intraspecific diversity. Little is known about the nondietary-mediated differences in fatty acid composition, but our results showed that nondietary fatty acid biomarkers can be useful tool in identifying variation.

Length of fish species with forked tails, such as the Lake Trout Salvelinus namaycush, can be measured as total (TL), fork (FL), or standard (SL) length, although individual studies of such species often rely on only one measurement, which hinders comparisons among studies. To determine if variation in the relationship between FL and TL among Lake Trout populations affected estimates of FL from TL, we compared length relationships within Lake Trout populations sampled in multiple years, among multiple locations within lakes, among lakes, and from all samples from across the species' range. Samples were from across the geographic range of the species and a wide range of lake sizes (1.31–82,100 km2) to represent the full range of variation in abiotic and biotic variables expected to influence the FL:TL relationship. The functional relationship for estimating FL (mm) from TL (mm) was FL = 0.91 × TL − 8.28 and TL from FL was TL = 1.09 × FL + 9.05. Error induced by length conversion was less when using a length relationship from a different year in the same lake than from a different area in the same lake or from a different lake. Estimation error was lowest when using an overall length conversion from across the species' range, which suggests the overall relationship could be used whenever a more accurate length conversion is not available for a population of interest. Our findings should be useful for providing a standardized model for converting FL to TL (and TL to FL) for Lake Trout, such as comparing published findings of different measurement units, converting measurement units by agencies or institutions that change sampling methods over time, or programs that use different sampling methods among areas.

Ships and boats may transport whole communities of non-indigenous species (NIS) through hull biofouling, some members of which may become invasive. Several studies have evaluated the diversity of these communities, but very few have analyzed the survival of organisms after their voyages into different and potentially inhospitable conditions. This factor is important to consider because the last port of call approach for risk assessments assumes that if the conditions observed in the last port of call are different from those observed in a receiving port, risks are diminished or null. Using an innovative experimental system, we tested the survival and recovery of the marine blue mussel (Mytilus edulis) and the freshwater zebra mussel (Dreissena polymorpha) by exposing them to adverse salinity conditions at varying temperatures to simulate ships and boats transiting to ports or marinas with contrasting environmental conditions. Both mussel species, which are well-known for their adaptability to new environments as aquatic NIS, survived better at colder temperatures, with blue mussels surviving up to 14 days in freshwater, and zebra mussels up to 8 days in marine water. This highlights the importance of considering the resistance of fouling organisms to adverse conditions in vector and species risk assessments.

Background We report compelling evidence suggesting a predation event of a pop-up satellite archival tagged anadromous Dolly Varden (Salvelinus malma) by a marine mammal during summer in the Beaufort Sea based on abrupt changes in temperature and vertical movements. This observation provides insight on predator avoidance behaviour by Dolly Varden and the predator’s feeding frequency while the tag was ingested. Based on published distribution and ecology information, we presumed the predator was a beluga whale (Delphinapterus leucas). Supplemental satellite telemetry data from previously tagged Dolly Varden and beluga whales were used to determine the extent of spatial and vertical overlap between species in the area where predation occurred. Results Prior to the predation event, depths and temperatures occupied by the tagged Dolly Varden averaged 1.1 m and 3.1 °C, respectively. On July 7, 2020, depths remained shallow apart from a sudden dive to 12.5 m (16:45 UTC) followed by a precipitous increase in temperature from 4.4 to 27.1 °C (16:52 UTC) suggesting predation by an endotherm. Subsequent readings indicated the endotherm had a resting stomach temperature of 36.1 °C. Including the predation event, eight separate feeding events were inferred during the 20-h period the tag was ingested (before presumed regurgitation) based on subsequent declines in stomach temperatures (mean decline to 31.1 °C) that took an average of 24.1 min to return to resting temperature. The predator occupied mainly shallow depths (mean = 2.3 m), overlapping with tagged belugas that spent 76.9% of their time occupying waters ≤ 2.5 m when frequenting the area occupied by tagged Dolly Varden in the Canadian Beaufort Sea in July. Back-calculation based on tag drift and mean displacement by tagged belugas indicated the predation likely occurred west of the Mackenzie Delta. Conclusion Our findings provide new information on both anti-predator behaviour by, and marine predators of, Dolly Varden in the Beaufort Sea. We provide the first estimate of feeding frequency and stomach temperature recovery in a presumed wild beluga, and evidence for shallow foraging behaviour by belugas. Elucidating the likely predator and exploring the extent of overlap between Dolly Varden and beluga whales contributes towards knowledge on the trophic interactions in the Beaufort Sea.

Climate change is transforming marine ecosystems through the expansion and contraction of species’ ranges. Sea ice loss and warming temperatures are expected to expand habitat availability for macroalgae along long stretches of Arctic coastlines. To better understand the current distribution of kelp forests in the Eastern Canadian Arctic, kelps were sampled along the coasts for species identifications and percent cover. The sampling effort was supplemented with occurrence records from global biodiversity databases, searches in the literature, and museum records. Environmental information and occurrence records were used to develop ensemble models for predicting habitat suitability and a Random Forest model to predict kelp cover for the dominant kelp species in the region – Agarum clathratum, Alaria esculenta, and Laminariaceae species (Laminaria solidungula and Saccharina latissima). Ice thickness, sea temperature and salinity explained the highest percentage of kelp distribution. Both modeling approaches showed that the current extent of arctic kelps is potentially much greater than the available records suggest. These modeling approaches were projected into the future using predicted environmental data for 2050 and 2100 based on the most extreme emission scenario (RCP 8.5). The models agreed that predicted distribution of kelp in the Eastern Canadian Arctic is likely to expand to more northern locations under future emissions scenarios, with the exception of the endemic arctic kelp L. solidungula, which is more likely to lose a significant proportion of suitable habitat. However, there were differences among species regarding predicted cover for both current and future projections. Notwithstanding model-specific variation, it is evident that kelps are widespread throughout the area and likely contribute significantly to the functioning of current Arctic ecosystems. Our results emphasize the importance of kelp in Arctic ecosystems and the underestimation of their potential distribution there.

We assessed the fish length – otolith length relationship (FL–OL) in Dolly Varden (Salvelinus malma malma) to verify proportional growth. A decoupling was detected during first ocean migration where fish growth was occurring at a greater rate than otolith growth. Because of this decoupling, the application of traditional back-calculation models overestimated the size-at-age in premigratory char. We developed modified back-calculation equations from existing traditional models to account for this decoupling based on discontinuous piecewise regressions. The new biological intercept breakpoint method (BI–BP) provided the most accurate representation of fish size-at-age throughout all life history stages when compared with known size-at-capture values in fish. The decoupling indicates that factors other than somatic growth are important for otolith accretion. Physiological changes during smoltification likely alter calcium uptake and thereby affect calcium deposition rates on otoliths during this short but biologically critical time period of life history. It is probable that species exhibiting similar complex ontogenetic shifts in life history will likely exhibit decoupling to some extent in the FL–OL relationship.

Among North American populations of northern form Dolly Varden (Salvelinus malma malma) exhibiting partial migration, the resident female life history is rarely encountered. Between 2012 and 2016, three sexually mature females confirmed as residents using otolith strontium analysis were captured from three rivers in the western Canadian Arctic ( 90th percentile). Early size-at-age of resident females either exceeded or were among the largest sizes compared to resident males and pre-smolt anadromous females. Residents had similar fecundity predicted for length and egg size (range 3.5–4.2 mm) compared to anadromous, although GSI (range 13.2–17.4%) was inconsistent among populations. Interestingly, one resident female attained a greater size-at-capture and fecundity than the smallest anadromous current-year spawner. Our results suggest that conditional mating tactics of Dolly Varden can be expressed by both sexes in multiple populations, and increases understanding of Dolly Varden life history diversity and bet-hedging strategies in partially migratory populations.

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

Mid-ocean ballast water exchange (BWE) is recommended for international vessels to minimize the transfer of nonindigenous species (NIS). When this cannot be accomplished due to safety concerns, alternate ballast water exchange zones (ABWEZ) may be used. A coupled-ice-ocean model with meteorological forcing and particle tracking was used to evaluate the relative risks from BWE along primary shipping routes into Canada's eastern Arctic. Relative risk to receiving habitats from BWE was calculated from the product of likelihood of exposure, likelihood of establishment, and habitat sensitivity to potential NIS. Modelling results indicate that existing ABWEZs in and around Lancaster Sound and Hudson Strait are among the areas of highest relative risk for introductions of NIS via ballast water. The deeper offshore regions of Labrador Sea and Baffin Bay should be considered as alternatives. However, further research is recommended to assess the risks of NIS associated with BWE in the Canadian Arctic.

The Canadian Arctic is receiving increased ship traffic, largely related to non-renewable resource exploitation and facilitated by climate change. This traffic, much of which arrives in ballast, increases opportunities for the spread of aquatic invasive species (AIS). One of the regions at greatest risk is the Hudson Bay Complex. A horizon scanning exercise was conducted using the semi-quantitative Canadian Marine Invasive Screening Tool (CMIST) to identify AIS of potential concern to the region. This screening-level risk assessment tool, uses documented information to answer questions related to the likelihood and impact of invasion. Species were analyzed by ecological categories (zoobenthos, zooplankton, phytobenthos) and taxonomic groups, with 14 species (out of 31) identified as being of highest relative risk. Crabs, mollusks, macrozooplankton and macroalgae were the taxonomic groups with the highest overall risk scores, through a combination of higher likelihood of invasion and impact scores relative to other taxa. Species that may pose the highest AIS risk are currently mainly distributed on the east and west coasts of the North Atlantic Ocean. Their distributions coincide with source ports and shipping pathways that are well connected to the Hudson Bay Complex. This first horizon scan to identify potential high-risk AIS for the Canadian Arctic incorporated two novel approaches into the CMIST analysis: i) use of the tool to assess two new ecological categories (phytobenthos and zooplankton), and ii) use of averaged CMIST results to interpret general risk patterns of ecological categories. This study is also the first to use CMIST scores to highlight common source regions and connected ports for the highest risk species. In a scenario of climate change and increasing ship traffic, this information can be used to support management actions such as the creation of watch lists to inform adaptive management for preventing AIS establishment, and mitigating associated environmental and economic impacts.

Ecological opportunities present during colonization of novel environments can drive divergent selection on traits, resulting in specialization of morphs to enhance efficient use of resources and, potentially, intraspecific divergence and ecological speciation. Thus, in an ecologically polymorphic species, differences in resource specialization should be found among morphs, and homogeneity in resource use expected within a morph. Using the piscivorous lake trout morph, one of four morphs in Great Bear Lake, we investigate whether specialization of trophic resources among individuals occurs within this single morph, which could indicate a potential for continued divergence. Four distinct dietary patterns of resource use within the piscivorous lake trout morph were detected from analyses of fatty acid composition. In general, feeding habits of different groups within the piscivorous morph were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity within individuals or behavioral differences among individuals may have caused the trophic variation within this morph. A low level of genetic differentiation indicated by variation at microsatellite loci was detected between exceptionally large-sized individuals (Giant sub-set) and other piscivorous individuals. Investigating a geologically young system that displays high levels of intraspecific diversity and focusing on dietary patterns of resource use variation of individuals suggested that individual specialization can occur within a trophic morph.

Because significant global changes are currently underway in the Arctic, creating a large-scale standardized database for Arctic marine biodiversity is particularly pressing. This study evaluates the potential of aquatic environmental DNA (eDNA) metabarcoding to detect Arctic coastal biodiversity changes and characterizes the local spatio-temporal distribution of eDNA in two locations. We extracted and amplified eDNA using two COI primer pairs from ~80 water samples that were collected across two Canadian Arctic ports, Churchill and Iqaluit, based on optimized sampling and preservation methods for remote regions surveys. Results demonstrate that aquatic eDNA surveys have the potential to document large-scale Arctic biodiversity change by providing a rapid overview of coastal metazoan biodiversity, detecting nonindigenous species, and allowing sampling in both open water and under the ice cover by local northern-based communities. We show that DNA sequences of ~50% of known Canadian Arctic species and potential invaders are currently present in public databases. A similar proportion of operational taxonomic units was identified at the species level with eDNA metabarcoding, for a total of 181 species identified at both sites. Despite the cold and well-mixed coastal environment, species composition was vertically heterogeneous, in part due to river inflow in the estuarine ecosystem, and differed between the water column and tide pools. Thus, COI-based eDNA metabarcoding may quickly improve large-scale Arctic biomonitoring using eDNA, but we caution that aquatic eDNA sampling needs to be standardized over space and time to accurately evaluate community structure changes., Ecology and Evolution, 8 (16), ISSN:2045-7758

The threat posed by invasive non-native species worldwide requires a global approach to identify which introduced species are likely to pose an elevated risk of impact to native species and ecosystems. To inform policy, stakeholders and management decisions on global threats to aquatic ecosystems, 195 assessors representing 120 risk assessment areas across all six inhabited continents screened 819 non-native species from 15 groups of aquatic organisms (freshwater, brackish, marine plants and animals) using the Aquatic Species Invasiveness Screening Kit. This multi-lingual decision-support tool for the risk screening of aquatic organisms provides assessors with risk scores for a species under current and future climate change conditions that, following a statistically based calibration, permits the accurate classification of species into high-, medium-and low-risk categories under current and predicted climate conditions. The 1730 screenings undertaken encompassed wide geographical areas (regions, political entities, parts thereof, water bodies, river basins, lake drainage basins, and marine regions), which permitted thresholds to be identified for almost all aquatic organismal groups screened as well as for tropical, temperate and continental climate classes, and for tropical and temperate marine ecoregions. In total, 33 species were identified as posing a 'very high risk' of being or becoming invasive, and the scores of several of these species under current climate increased under future climate conditions, primarily due to their wide thermal tolerances. The risk thresholds determined for taxonomic groups and climate zones provide a basis against which area-specific or climate-based calibrated thresholds may be interpreted. In turn, the risk rankings help decision-makers identify which species require an immediate 'rapid' management action (e.g. eradication, control) to avoid or mitigate adverse impacts, which require a full risk assessment, and which are to be restricted or banned with regard to importation and/or sale as ornamental or aquarium/fishery enhancement. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/)., Cefas Science Excellence fund; [TKP2020-NKA-16], This study is dedicated to our co-author, the late Prof. Olaf Weyl, whose sudden passing during field work in November 2020 was received by us with great sadness. This study represents a contribution to the term of reference 'd' (Advance knowledge base to further develop indicators to evaluate the status and impact of non-indigenous species in marine environments) of the ICES working group on Introductions and Transfers of Marine Organisms. The participation of GHC was supported by the Cefas Science Excellence fund. AW and AF were supported by TKP2020-NKA-16 project.

A rise in Arctic shipping activity resulting from global warming and resource exploitation is expected to increase the likelihood of aquatic invasive species (AIS) introductions in the region. In this context, the potential threat of future AIS incursions at a Canadian Arctic regional scale was examined. Habitat suitability under current environmental conditions and future climate change scenarios was projected for a subset of eight potential invaders ranked as having a high risk of establishment in the Canadian Arctic based on dispersal pathways/donor regions, biological attributes and invasion history: (1) Amphibalanus improvisus, (2) Botrylloides violaceus, (3) Caprella mutica, (4) Carcinus maenas, (5) Littorina littorea, (6) Membranipora membranacea, (7) Mya arenaria and (8) Paralithodes camtschaticus. Habitat modelling was performed using MaxEnt based on globally known native and non-native occurrence records and environmental ranges for these species. Results showed that under current environmental conditions the habitat is suitable in certain regions of the Canadian Arctic such as the Hudson Complex and Beaufort Sea for L. littorea, M. arenaria and P. camtschaticus. Under a future climate change scenario, all species showed poleward gains in habitat suitability with at least some regions of the Canadian Arctic projected to be suitable for the complete suite of species modelled. The use of these models is helpful in understanding potential future AIS incursions as a result of climate change and shipping at large spatial scales. These approaches can aid in the identification of high risk regions and species to allow for more focused AIS monitoring and research efforts in response to climate change.

Aim: Ballast water is a major vector of non-indigenous species introductions world-wide. Our understanding of population dynamics of organisms entrained in ballast is largely limited to studies of zooplankton and phytoplankton. Bacteria are more numerous and diverse than zooplankton or phytoplankton, yet remain comparatively understudied. We apply a metagenomics approach to characterize changes in the microbial ballast water community over the course of three voyages on one ship, and assess the effects of ballast water exchange (BWE), spring/summer sampling month and time since voyage start. Location: Quebec City and Deception Bay, Quebec, and the coastal marine region offshore of eastern Canada. Methods: We used universal primers to Ion Torrent sequence a fragment of the bacterial 16S ribosomal DNA for samples collected over three voyages of one ship between Quebec City and Deception Bay in June, July and August 2015. We compared richness (total number of species in the community) and diversity (accounts for both species abundance and evenness) using linear mixed-effects analysis and compared community composition using non-metric multidimensional scaling and permutational multivariate analysis of variance. Initial comparisons were between months. Subsequent analyses focused on each month separately. Results: Ion Torrent sequencing returned c. 2.9 million reads and revealed monthly differences in diversity and richness, and in community structure in ballast water. June had higher richness and diversity than either July or August, and showed most clearly the effect of BWE on the microbial community. Main conclusions: Our results suggest that environmental conditions associated with different spring/summer sampling months drive differences in microbial diversity in ballast water. This study showed that BWE removes some components of the freshwater starting microbial community and replaces them with other taxa. BWE also changed proportional representation of some microbes without removing them completely. It appears that some taxa are resident in ballast tanks and are not removed by BWE. © 2017 John Wiley & Sons Ltd

Populations of northern Dolly Varden (Salvelinus malma malma) exhibit partial seaward migration, yet little is known about this phenomenon in Dolly Varden populations. Our study analyzed data from three different Dolly Varden populations in the western Canadian Arctic in order to determine if: (1) differences in size-at-first seaward migration exist between fish that migrate at early and late ages among populations inhabiting different river systems, and (2) annual growth influences anadromous or resident life history choice. Otolith strontium analysis and back-calculation were used to determine age- and size-at-first seaward migration, respectively. Differences in age- and size-at-first seaward migration were determined across river system and migration age. Back-calculated fish lengths were compared using a mixed effect model to determine how early growth influences migratory tactics (early or late aged smolt, or resident). Our results indicate that fish exhibiting faster early growth migrated in earlier years and at smaller sizes than slower growing fish, however size- and age-at first seaward migration varied by river system. Faster growing Dolly Varden tended to become either residents or early smolts, while slower growth was associated with smolting later in life. This is contrary to life history theory where the fastest growing fish in a population should mature as a resident. Our results indicate factors other than growth may be influencing life history ‘decisions’ in Dolly Varden. Future work on growth efficiencies and metabolic rates is needed to assess how they affect migratory behaviours.

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Census population size (N c ) is crucial to the development of resource management strategies, however, monitoring the effective population size (N e ) of managed populations has proliferated because of this parameter’s relationship to the short-term impacts of genetic stochasticity and long-term population viability. Thus, having a sound understanding of both N c and N e , including population connectivity, provides valuable insights into both the demographic and genetic risks to extinction. Here, we assessed microsatellite DNA variation in four (of five known) anadromous northern Dolly Varden (NDV, Salvelinus malma malma) populations from Canada’s western Arctic region, to estimate N e using both temporal-based and single-sample estimators and to test for associations between N e and N c . We also employed approximate Bayesian computation (ABC) to evaluate several evolutionary scenarios that have potentially shaped contemporary population structure in this species, focusing particularly on population size and connectivity. We found evidence for moderate to large contemporary and historical N e , suggesting that short- and long-term extinction risks are low for these populations. Estimates of contemporary and long-term N e were variable within and among populations and overall estimates could not be reliably linked with N c or available spawning habitat. The overall estimate of N e /N c , was 0.152 and ranged from 0.024 to 0.442 when including errors around the estimate of N e and N c . Finally, ABC analyses suggest that NDV had a common origin followed by divergence in isolation while maintaining large effective sizes, but also that these populations were bottlenecked in the past, likely the result of post-glacial colonization processes. These results corroborate indications of limited gene flow at present, indicating independent demographic and evolutionary trajectories that imply NDV is best managed on a per-river-population basis. Overall, the results of this study further our general understanding of N e , N e /N c and demographic independence in NDV, and provide a comprehensive and quantitative assessment of the potential genetic and demographic risk status of Arctic anadromous salmonids, including baselines for future monitoring.

A generalist strategy, as an adaptation to environmental heterogeneity, is common in Arctic freshwater systems, often accompanied, however, by intraspecific divergence that promotes specialization in niche use. To better understand how resources may be partitioned in a northern system that supports intraspecific diversity of Lake Trout, trophic niches were compared among four shallow‐water morphotypes in Great Bear Lake (N65° 56′ 39″, W120° 50′ 59″). Bayesian mixing model analyses of stable isotopes of carbon and nitrogen were conducted on adult Lake Trout. Major niche overlap in resource use among four Lake Trout morphotypes was found within littoral and pelagic zones, which raises the question of how such polymorphism can be sustained among opportunistic generalist morphotypes. Covariances of our morphological datasets were tested against δ13C and δ15N values. Patterns among morphotypes were mainly observed for δ15N. This link between ecological and morphological differentiation suggested that selection pressure(s) operate at the trophic level (δ15N), independent of habitat, rather than along the habitat‐foraging opportunity axis (δ13C). The spatial and temporal variability of resources in Arctic lakes, such as Great Bear Lake, may have favored the presence of multiple generalists showing different degrees of omnivory along a weak benthic–pelagic gradient. Morphs 1–3 had more generalist feeding habits using both benthic and pelagic habitats than Morph 4, which was a top‐predator specialist in the pelagic habitat. Evidence for frequent cannibalism in Great Bear Lake was found across all four morphotypes and may also contribute to polymorphism. We suggest that the multiple generalist morphs described here from Great Bear Lake are a unique expression of diversity due to the presumed constraints on the evolution of generalists and contrast with the development of multiple specialists, the standard response to intraspecific divergence.

Using a PIT detection system and two in-stream, swim-through antennas, we examined the movements of Arctic Grayling Thymallus arcticus through a low-gradient (

Phenotypic variation within populations is common in many salmonids, especially when inhabiting northern postglacial systems. We compared life-history traits among four lake trout morphs co-existing in the shallow-waters of Great Bear Lake (Northwest Territories, Canada). Adult growth rate, age- and size-at-maturity, and survival differed among morphs, consistent with their degree of foraging specialization and predictions from foraging theory, e.g., reduced somatic growth and higher reproductive investment in the generalist morph, high growth throughout life in the piscivorous morph, and intermediate life-histories in the more benthic- and pelagic-oriented morphs. Fecundity and egg size also varied among morphs. However unexpected findings also arose, such as comparable immature growth rates among morphs. Other traits, such as a high proportion of resting individuals among all morphs, suggest life-history adaptations to northern latitudes. Longer resting periods are likely needed to obtain enough energy for reproduction, and may also allow greater investment in post-maturation growth. Overall, lake trout from Great Bear Lake demonstrated remarkable longevity and exceptional asymptotic sizes, even for a northern freshwater ecosystem. Our study provides new insights into life-history evolution among lake trout morphs that use different food sources and habitats. In addition, it contributes to our understanding of this complex aquatic ecosystem, which exhibits one of the highest known levels of intraspecific diversity among freshwater fish.

Though Lake Whitefish are ecologically, culturally and economically important to aboriginal communities in the Northwest Territories, Canada, growth characteristics of the fish populations have not received extensive interpretations, resulting in a lack of quantitative information to support fisheries management efforts in subarctic great lake systems. The overall objective of this study is to investigate spatiotemporal variations of growth characteristics of Lake Whitefish populations in Great Slave Lake (GSL) from 1972–2009. Using hierarchical Bayesian statistics, we structured four candidate growth models: generalized (GGM), logistic (LGM), Gompertz (PGM), and von Bertalanffy (VBM), with four parameterization scenarios combining all possible options of varying or constant L∞ and K. In terms of deviance information criterion (DIC) and multimodel inference (MMI), the plausibility of the candidate models was evaluated to select the best combinations of growth models and the parameter scenarios. The GGM with varying L∞ and K best delineated the fish growth characteristics in almost all areas of GSL, while the fish growth model parameterized with constant L∞ and varying K performed best in the shallow western basin. The VGM where L∞ and K were varied partially described fish growth in the shallow waters. Applying the MMI-based growth analysis, we found that smaller and slower-growing fish were mainly distributed in deep waters, while larger and faster-growing fish inhabited shallow waters. These spatiotemporal variations of fish growth characteristics have been attributed to the presence of coupled impacts derived from both climate-driven and anthropogenic events.

Local (e.g., habitat compensation activities) and regional (e.g., climate-related range expansion) events that are expected to increase in northern Canada can facilitate movement of fishes into aquatic ecosystems from which they were previously absent. Successful colonization would change fish community structure and potentially alter food web dynamics. We compared the trophic ecology, growth, and body condition of Lake Trout ( Salvelinus namaycush ) in small, tundra lakes that varied in fish community structure to help understand effects of colonization on this key species. Complementary stable isotope and stomach content analyses indicated that Lake Trout foraging differs between lakes with and without multiple large-bodied fishes. In lakes with a single potential competitor, trout consumed primarily pelagic zooplankton, but focused on more littoral resources in the presence of multiple large-bodied fishes. Population trophic niche width and inter-individual variation in Lake Trout diet were larger in lakes with multiple competitors, whereas Lake Trout populations in lakes with only one other large-bodied species were in better body condition. Our findings highlight the potential sensitivity of northern Lake Trout populations to colonizing fish species.

Coastal habitats provide unique conditions allowing a specific diversity of species to establish. However, in the Canadian Arctic, it may experience a growing number of impacts such as oil spills and aquatic invasive species. Effective, low-cost sampling methods are then required to obtain baseline data on Arctic species. In this context, the eSPACE project developed a classification of habitats by videography using substrate and geomorphology. To verify the relationships between this habitat classification and the biological and functional composition, coastal benthic communities and associated habitats were characterized in Churchill, Manitoba. Differences between biological composition and functional traits of each habitat were found which allow for direct information on the relative biological importance of sampled habitats and help validate the classification of habitats.

The risk of aquatic invasive species (AIS) introductions in the Arctic is expected to increase with ongoing trends of greater shipping activity, resource exploitation, and climate warming in the region. We identified a suite of AIS (benthos, zooplankton and macroalgae) with the greatest likelihood of introduction and impact in the Canadian Arctic using the Canadian Marine Invasive Screening Tool. The top sixteen riskiest species (mainly benthic) were then modelled to predict the potential spatial distributions (habitat modelling using Maximum Entropy) at an Arctic scale. Modelling was conducted under present environmental conditions and under two future global warming scenarios (2050 and 2100). Results show that hotspots or regions where suitable habitat is more densely accumulated for modelled AIS are in the Hudson Complex, Chukchi / Eastern Bering Sea, and Barents / White Sea. Most taxonomic groups showed a trend for a positive poleward shift in the future, increasing from the present time to the end of the century. This approach will aid in the identification of present and future high-risk areas for AIS in response to global warming.

Assessment of anadromous northern-form Dolly Varden Salvelinus malma malma in the Western Canadian Arctic requires reliable methods for estimating ages. Additionally, conservation efforts warrant determining whether fin rays provide a non-lethal alternative to otoliths. Precision and bias of whole and sectioned otoliths, and sectioned pectoral and pelvic fin rays were examined. Two age readers with different levels of experience ageing this species read each structure three times. Coefficient of variation (CV) was calculated to measure precision, and age bias plots were created for each method of preparation/structure within and between readers. The experienced reader demonstrated the highest precision with sectioned otoliths (CV = 1.6 %) followed by whole otoliths (CV = 4.2 %) while pectoral and pelvic fins were the lowest, CV = 7.7 % and 7.5 %, respectively. The age bias plot showed little difference between whole and sectioned otoliths, although greater imprecision/bias was evident for whole otoliths at age ≥9. Compared to otoliths, fin rays produced younger age estimates starting at 5 years; however, pelvic fins were more biased towards younger estimates than pectoral fins. The less experienced reader had greater inconsistencies, tending to overage younger and underage older samples for all methods compared to the more experienced reader, underscoring the importance of experience when estimating age for this species. We conclude that both types of fin rays are a poor non-lethal alternative to otoliths for fish ≥5 years and recommend an experienced ager could use whole otoliths up to age 8 and sectioned otoliths for fish ≥9 years (>500 mm fork length).

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

The study of cisco diversity in inland lakes of North America has been plagued by taxonomic uncertainty linked to high phenotypic plasticity and an ongoing reliance on morphology to differentiate species. More recently, this uncertainty has hindered the development of conservation plans and status assessments of ciscoes. This study presents the first range-wide comparison of morphological and genetic variation between Cisco (Coregonus artedi) and Shortjaw Cisco (C. zenithicus). Using morphological and genetic data from 17 lakes, three sets of analyses were undertaken to evaluate alternate hypotheses explaining the pattern of cisco phenotypic diversity in inland lakes. Morphotypes (MTs) representing the two taxa were phenotypically distinct (largely reflective of differences in gill raker number and jaw morphology) within lakes but highly variable across lakes. Shortjaw Cisco was only recognizable when compared to sympatric Cisco and some populations were morphologically similar to Cisco from other lakes. Analysis of AFLP data revealed two genetic clusters that conformed to differences in geography (eastern and western groups), rather than hypothesized taxonomic boundaries. Genetic variation strongly suggests that each of these unique sympatric pairs of MTs originated recently and locally, in parallel, from the ancestral Cisco. Phenotypic and genetic distinctiveness between MTs were not related. MTs were sometimes clearly recognizable despite a lack of genetic differentiation, suggesting that the canalization of phenotypic plasticity is unevenly completed across lakes. These results provide evidence that the taxon-based approach is clearly inadequate for the protection of Shortjaw Cisco. In Canada, status assessment should aim to identify lake-specific designatable units (DU). Given the idiosyncratic nature of each instance of Shortjaw Cisco, it is expected that the strength of morphological, biological, ecological and genetic evidence for individual DUs will vary among lakes.

We examined the effectiveness of three fishpasses (two gabion-style pool–weir fishpasses and one nature-like choke-and-pool fishpass) at enhancing connectivity among three small, headwater lakes as part of a fish habitat compensation project in the Barrenlands region of the Northwest Territories. We quantified fish attraction and passage efficiency of fishpasses using PIT antennae, and compared fish use of fishpasses to reference streams using visual and electrofishing surveys for 1 year before and 2 years after their construction. We did not detect, observe, or capture any fish in either of the gabion-style pool–weir fishpasses during the first year after construction, and these two fishpasses were subsequently retrofitted to improve their hydraulic performance. After retrofits were completed, we still did not detect any tagged fish (≥150 mm) migrating through the two fishpasses using PIT telemetry, but identified some small fish moving downstream through these fishpasses during visual and electr...

It has been well documented in previous research that otoliths are the preferred hard structure for estimating age in coregonids. However, the slower growth due to short growing seasons experienced by populations in the subarctic region of the boreal zone may alter the utility of alternative nonlethal structures for estimating age. We compared the three most commonly used age estimation structures (otoliths, pectoral fin rays, and scales) for Lake Whitefish Coregonus clupeaformis in a northern (above 50°N) population from Great Slave Lake. This study provides new perspectives regarding the use of different aging structures with fish populations typical of subarctic and arctic environments. Results of ANOVA showed that reader confidence, within-reader precision, and the age estimates themselves were all affected by age structure; reader confidence also varied with age-class. Reader confidence was highest for age estimates from otoliths, followed by pectoral fin rays and then scales. Similarly, with...

Otolith strontium and multi-year mark-recapture information were used to characterize associations between migration patterns and spawning frequencies in an anadromous Dolly Varden (Salvelinus malma) population (Rat River, Northwest Territories, Canada) that undertakes a long migration between freshwater spawning/overwintering (Fish Creek; a tributary to Rat River) and marine feeding habitats (Beaufort Sea) (~800 km round trip). Reconstructions of lifetime annual migration histories among otolith annuli was matched to information on reproductive status (current-year 'spawner' or 'non-spawner') that was known in two different, sometimes successive, years for each fish. Two migratory life histories were observed: fish either migrated annually after smoltification or periodically skipped an annual ocean migration to remain in freshwater and spawn. Different spawning frequencies were detected where fish not migrating annually tended to spawn in alternate years (84.6%) more often than those migrating annually (50%). Additionally, annually migrating fish had lower longevity (≤9 years vs. ≤13 years). The evaluation of differences in spawning frequency between sexes, independent of migration tactic, revealed males (84.6%) skipped spawning more often than females (51.2%) suggesting fitness trade-offs between life histories differ between sexes. Further, some fish returned from the sea considerably earlier than the majority of other current-year migrants. Our findings demonstrate intrapopulation diversity in migration behaviour and reproductive frequency.

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

Sympatric diversification in Lake Trout is generally linked to differences in habitat use (especially depth) as a result of foraging on different prey items. However, extensive sympatric divergence has taken place in the shallow waters (≤30 m) of Great Bear Lake, with multiple Lake Trout morphs varying in head and fin characteristics. To investigate diet partitioning as a potential explanatory mechanism for this diversification, we assessed trophic characteristics and relationships among four sympatric shallow-water morphs of Lake Trout via analyses of fatty acids and stomach contents. Fatty acids and stomach contents both identified Lake Trout, Cisco and Mysis as key prey items in Lake Trout diets. Interestingly, terrestrial invertebrates were also seasonally important among morphs, reflecting temporal variability of available prey in this arctic lake. Some diet partitioning was observed among morphs; Morph 1 was characterised as a generalist, Morph 3 was more benthic-oriented, and Morphs 2 and 4 were mainly pelagic feeders. Of the latter, Morph 4 was the most specialised, whereas Morph 2 exhibited alternative feeding tactics of benthic cannibalistic and pelagic piscivorous feeding. Our findings demonstrate that complementary dietary methods can elucidate habits of opportunistic feeders, a task that can often be problematic, given their complex and variable diets. Our results add new information and perspectives on the current model of Lake Trout differentiation, demonstrating niche partitioning based on benthic versus pelagic habitat use and generalist versus specialist feeding tactics.

Great Bear Lake is the most northerly lake of its size and provides unique opportunities for intraspecific diversification. Despite increasing attention to intraspecific polymorphism, several knowledge gaps remain (e.g. determining the extent of intraspecific diversification in large relatively pristine lakes and at which spatial scale it can occur). We focused on geographical patterns of morphological differentiation within lake trout (Salvelinus namaycush) to describe two levels of intralake diversification in Great Bear Lake. We used a combination of geometric and traditional linear measurements to quantify differences in body shape, head shape, and fin and body lengths among 910 adult lake trout from the five distinct arms of Great Bear Lake. Although head and fin linear measurements discriminated the three common morphotypes at the whole-lake level, inter-arm variation in body shape was observed within each morphotype. A comparison of genetic and morphological distance matrices revealed the lack of an association between the two sets of data, although both comparisons revealed an association in the inter-arm variation patterns among morphotypes, suggesting a phenotypically plastic response to distinct environments. The whole-lake and inter-arm morphological variation observed within lake trout demonstrates the importance of considering scale, especially across large lakes that exhibit marked complexity and a variety of freshwater habitats. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114, 109–125.