Simon DePasquale

Objective: Inuit subsistence fishers in Kugluktuk, Nunavut, Canada, have noticed changes in the timing and locations of their catches of Arctic Char Salvelinus alpinus and northern form Dolly Varden S. malma malma (collectively referred to by the community as “char”) in the past ∼20 years. In response, an ongoing research program was formed to study char in partnership with the Kugluktuk Hunters and Trappers Organization. The occurrence of sympatric populations of anadromous Arctic Char and Dolly Varden is rare but was recently identified in Coronation Gulf, Nunavut, where char populations were conventionally understood to be composed of only Arctic Char. To date, no studies have compared use of marine habitats between sympatric anadromous Arctic Char and Dolly Varden. Our objective was to identify high-use areas for each species, provide a broad comparison of habitat use (riverine, estuarine, nearshore marine, offshore island marine, and offshore marine) between species, and assess differences between species in minimum total distance traveled as calculated from observed movements between receiver stations. Methods: Between 2019 and 2023, we used acoustic telemetry to document the marine movements of sympatric anadromous Arctic Char and northern form Dolly Varden. Using network analysis, we investigated and compared the marine movements of individuals from each species that spent ≥28 d in the marine environment. Results: We observed highest use of estuarine and nearshore habitats by both Arctic Char and Dolly Varden. Dolly Varden had significantly larger mean corrected node strength and residency index values at offshore island habitats compared with Arctic Char in 2020, 2021, and 2023. Dolly Varden used the offshore marine environment more than Arctic Char; however, differences were not significant. Median standardized (per hour detected) minimum distances that Arctic Char and Dolly Varden were detected traveling in the marine environment were 107 and 122 m, respectively. Data are provided to enable reanalyses with different marine residency thresholds. Conclusions: Our findings indicate that stewardship of estuarine and nearshore marine habitats will benefit anadromous populations of Arctic Char and Dolly Varden near Kugluktuk. While we found that Dolly Varden had higher use of offshore marine habitats than Arctic Char, our results should be interpreted with caution because of low sample sizes and limited offshore receiver coverage. Our study provides a foundation for future research comparing the habitat use and ecology of sympatric anadromous forms of Arctic Char and Dolly Varden, which may support the development of species-specific restoration and stewardship measures.

Anadromous Arctic char ( Salvelinus alpinus ) and northern form Dolly Varden ( Salvelinus malma malma ) are highly valued by Indigenous communities in northern Canada. Rapid, ongoing environmental changes are affecting populations of both of these iteroparous species, and understanding variability in life‐history tactics is essential for assessment of current and future impacts. The Coppermine River, Nunavut, provides a unique opportunity to study anadromous life‐history types of Dolly Varden and Arctic char that occur in sympatry in fresh water and have documented inter‐ and intra‐specific variability in overwintering locations. We used acoustic telemetry and physical samples from community collection programs to infer that Arctic char overwintered in easily accessible habitats in the lower reaches of the Coppermine River, likely in non‐spawning years, and that spawning likely occurs in rivers other than the Coppermine. Younger and smaller Dolly Varden overwintered in the river below a substantial obstacle (a large cascade), along with some larger adults that we suggest skipped spawning. Larger Dolly Varden, including potential spawners, migrated above the cascade and overwintered in the upper reaches of the Coppermine River. Arctic char exhibited distinct patterns of return migration to fresh water that were consistent with intent to overwinter below the cascade. Dolly Varden that overwintered above the cascade exhibited distinct patterns of return migration that were consistent with directed movements. Patterns of return migration to fresh water for Dolly Varden that overwintered below the cascade suggested some individuals intended to overwinter below the cascade, whereas others may have attempted to overwinter in the upper reaches of the river but failed to ascend the cascade. The patterns and variability we observed in overwintering location and return migration to fresh water have important implications for community‐based management of the local fishery, provide insights into the ecology and adaptability of Arctic char and Dolly Varden, and highlight a need for additional information regarding spawning locations and spawning frequency in this system.

Shifts in migration timing in response to climate change have implications for fitness and survival of cold-adapted species. We used acoustic telemetry to investigate and compare environmental influences on return to fresh water between sympatric anadromous Arctic char ( Salvelinus alpinus) and Dolly Varden ( Salvelinus malma malma), and between overwintering locations (above or below an obstacle—a substantial cascade). Both Arctic char and Dolly Varden that overwintered below the cascade returned to fresh water later in the year, when sea surface temperature was warm and river temperature was cool, whereas Dolly Varden that overwintered above the cascade returned to fresh water earlier in the year, at cooler sea surface temperatures and during warm and likely stressful river temperatures. Ascension of the cascade by Dolly Varden (no Arctic char were observed to ascend the cascade) was likely assisted by high tide but unaffected by other environmental factors, including temperature. Fish demonstrated plasticity in response to inter-annual variation in environmental conditions, but may experience decoupling of environmental cues and suitable migratory conditions, which could impact persistence of these ecologically and culturally important species.

Catch-and-release angling exposes fish to challenges that may result in sub-lethal effects or mortality. Lake trout (Salvelinus namaycush) undergo high rates of release because of size-based harvest regulations or voluntary angler behaviour. Here, we examine short-term impairment in lake trout angled during the summer (n = 74) and fall spawning period (n = 33) to inform best practices for angling. Immediately following capture or 0.5 h post-capture, fish underwent reflex and barotrauma assessments, and a small blood sample was collected. Fish were also fitted with an externally mounted biologger equipped with depth, temperature and tri-axial acceleration sensors, that was tethered to allow retrieval of the logger after 14 min. In the summer, reflex impairment and barotrauma at 0 and 0.5 h were significantly correlated. Loss of orientation and bloating were the most observed indicators. Larger fish and those captured at increased depth had higher barotrauma scores, while prolonged fight times decreased the barotrauma score regardless of sampling time. Plasma cortisol, lactate and glucose increased 0.5 h after capture, and extracellular and intracellular pH decreased, all signs that angling was inducing a metabolic response. However, no relationships were found between blood indices and mortality (18.9%). The time required to reach maximum depth after release was longer for fish with increased air exposure but shorter for those with longer fight times. During the fall, fish displayed no mortality or reflex impairment. Anal prolapse was the most observed indicator of barotrauma but only observed in females. Blood indices were most altered 0.5 h after capture, with increased cortisol values for fish that were female, particularly large or captured at deeper depth. Locomotor activity was highest for males and increased with depth. Together, our findings suggest that the effects of catch-and-release angling may be dependent on several factors, including sex, season and angling depth.

Catch-and-release (C&R) angling is a conservation-oriented practice intended to reduce the impact recreational angling has on fish populations. Even though most recreationally angled fish are released, little is known about how C&R angling impacts fish at the cellular or tissue level. As the first to explore the impacts of C&R angling on mRNA abundances, our study aimed to identify how the stress of angling influenced metabolism, acid–base regulation and cellular stress in the gills of lake trout (Salvelinus namaycush). Because gills are responsible for metabolic gas exchange, are crucial sites of acid–base homeostasis and respond to stressors quickly, we hypothesized that the relative mRNA abundance of genes related to these three physiological processes would be altered after angling. We took gill samples of live lake trout at 0, 2 or 48 h after fish were angled by rod and reel, and then used quantitative PCR (qPCR) to measure the relative abundance of nine candidate mRNA transcripts. Heat shock protein 70 (hsp70) mRNA levels significantly increased over 5-fold 2 h after angling, indicating a potential activation of a cytoprotective response. However, contrary to our hypothesis, we observed no change in the relative mRNA abundance of genes related to metabolism or acid–base regulation in response to C&R angling within a 48-h period. As C&R angling can negatively impact fish populations, further use of transcript-level studies will allow us to understand the impact C&R has on specific tissues and improve our knowledge of how C&R influences overall fish health.