Occupancy of young-of-year Arctic grayling (Thymallus arcticus) in Barrenland streams

Arctic grayling (Thymallus arcticus) is an iconic fish species that is present across the remote subarctic Barrenlands, yet our lack of understanding of their distributional patterns constrains predictions of anthropogenic effects on Barrenland populations. These adfluvial fish rely on seasonal lake-stream connections to migrate, spawn, and rear. We address knowledge gaps on what Barrenland stream attributes are suitable for rearing young-of-year Arctic grayling. Visual surveys of young-of-year Arctic grayling were conducted in 48 streams near Baker Lake, Nunavut, Canada. Occupancy modeling was used to relate stream habitat and landscape variables to fish presence/absence. The best predictors of occupancy were total area of contributing upstream lakes and landcover (upland/lowland); stream basins with larger contributing upstream lake area and more lowland cover were more likely to be occupied. Results suggest that occupancy reflects reliability of stream connectivity throughout the open water season and across years. The occupancy model developed here can adequately predict stream suitability for young-of-year Arctic grayling using lake area and land classification data that are remotely accessed. This may lessen the considerable financial and logistical constraints of conducting field research on Arctic grayling in the vast Barrenlands and facilitate more directed field programs to inform conservation and mitigation plans.

Rating the potential suitability of habitat in Michigan stream reaches for Arctic grayling

Arctic Grayling Thymallus arcticus were historically found throughout the northern half of Michigan’s Lower Peninsula but were extirpated from the state by 1936. By addressing issues from previous reintroduction efforts and employing instream rearing (Remote Site Incubator) approach to stocking, numerous partners are working to reintroduce Arctic Grayling to Michigan with hopes of reestablishing self-sustaining populations. With over 47,000 km of coldwater stream habitat in the state and limited numbers of eggs for reintroductions, a prioritization framework was needed to provide a standardized, fine-scale method for rating suitability of streams for reintroductions. Through facilitated discussions with stakeholders and experts, we developed an overall prioritization framework for rating Michigan streams with components evaluating a reach’s thermal, instream habitat, biological, and connectivity characteristics. Within the context of this broader framework, we developed the habitat rating component for assessing suitability of instream conditions for egg, fry, juvenile, and adult life stages of Arctic Grayling. Life-stage specific habitat metrics and scoring criteria from this effort were used to rate habitat conditions for 45 reaches in tributaries of Michigan’s Manistee River, enabling identification of reaches likely having instream habitat most suitable for Arctic Grayling. Numbers of reaches meeting or exceeding 60%, 70%, and 80% of the maximum score for overall habitat suitability were 31, 8, and 1. Upon completion of the fish assemblage and connectivity components, the prioritization framework and habitat rating process described here will be used for comparing suitability among streams throughout the historic range of Arctic Grayling in Michigan and guiding reintroduction efforts. Though it will take considerable time before instream habitat suitability criteria can be evaluated for all life stages of Arctic Grayling in Michigan, the collaborative stream prioritization framework developed for Arctic Grayling reintroduction can be readily adapted to reintroduction efforts for other species elsewhere.

Range Extension of Northern Form Dolly Varden (Salvelinus malma malma) to the Upper Arctic Red River Watershed, Northwest Territories, Canada

Northern form Dolly Varden is an anadromous char with significant ecological value found in high-gradient rivers of the Western Arctic. Because of declines in population abundance, Dolly Varden was recently designated as “Special Concern” under the federal Species at Risk Act. This species is also of great cultural and dietary significance to Indigenous Peoples of many communities in the Western Arctic; thus, expanding knowledge of the distribution, biology, and essential habitat is an important priority. We present results of a fisheries survey in the headwaters of the Arctic Red River, Northwest Territories, that focused on confirming the presence of Dolly Varden. Of 143 fish captured among 12 sampling locations, two were Arctic grayling (Thymallus arcticus), 33 were slimy sculpin (Cottus cognatus), and 108 were char identified using qualitative and quantitative morphological features. A subsample of 44 char voucher specimens were frozen whole and later identified using a linear discriminant function (LDF) based on meristic counts and morphological measurements, and a mitochondrial DNA genetic marker. LDF scores indicated that char collected in the Arctic Red River were northern form Dolly Varden. Genetic analysis showed that all but one char possessed mitochondrial DNA sequences common in northern form Dolly Varden from Canada. Our results confirm the presence of Dolly Varden in the Arctic Red River headwaters, extending the confirmed known distribution of this taxon in the Northwest Territories approximately 450 km south and 100 km east of previously delimited areas.

Parasites of graylings (Thymallidae: Thymallus) from the northern continental coast of the Okhotsk Sea

For the first time, generalized data on parasites of two subspecies of arctic grayling (Thymallus arcticus pallasi and Th. a. mertensi) from the largest salmon rivers of the northern coast of the Okhotsk Sea, as the Taui, Yama and Gizhiga, are presented. In total, 39 species of parasites are found including 38 helminth species belonging to 26 genera, 19 families, 5 classes and 3 types (Plathelminthes, Nemathelminthes, and Acanthocephales), and 1 parasitic copepod (Crustacea; Arthropoda). Among the flatworms, trematodes have the highest species diversity — 19 species belonged to 8 genera of 6 families, and cestodes are presented by 6 species (6 genera of 5 families). Nematodes are presented by 8 species (8 genera of 5 families), and acanthocephalans — by 5 species (4 genera, 3 families, 2 classes). The graylings parasites are distributed with 2 ecological groups: the freshwater parasites including 29 species (4 cestodes, 16 trematodes, 5 nematodes, 3 acanthocephalans, and 1 copepod) and the marine parasites including 10 species (2 cestodes, 3 trematodes, 3 nematodes, and 2 acanthocephalans). Th. a. mertensi from the Taui River basin is distinguished by the highest diversity of parasites (32 species), their high diversity is observed for the same species from the Gizhiga (20 species), and for Th. a. pallasi from the Yama (24 species), as well. More than a half of helminths (22 species) are noted by medical and veterinary importance and/or are able to spoil organoleptic properties of the seafood.

Genetic monitoring informs conservation status and trend of Arctic grayling at the southern edge of their distribution

The number of effective breeders (Nb) has been touted as a means to monitor freshwater fishes, but the realized application of Nb has been limited. Using genetic monitoring data for two Arctic grayling (Thymallus arcticus) populations of conservation concern, we describe temporal trends in genetic variation and Nb, determine how sampling and variance in reproductive success influence estimates of Nb, and quantify the relationship among Nb, effective population size (Ne), and adult abundance (Nc). Temporal trends in allelic richness (AR) and Nb tracked known or suspected population trajectories. Nb increased in one population where there has been extensive conservation action, and both Nb and AR tracked a decline in the other population where harsh winter conditions have resulted in overwinter mortality events. After accounting for population demography, Ne estimates for each population were 190.7 and 308.8. Overall, this study demonstrates that temporal genetic data effectively resolve demographic and evolutionary status and trend in Arctic grayling, provides insight into the demographic factors that influence genetic variation, and emphasizes the value of temporal genetic data for conservation and management.