Marine habitat use and movement of sympatric anadromous Dolly Varden and Arctic Char in the Canadian Arctic

Abstract 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.