Marine and freshwater habitats used by sympatric anadromous Arctic Char (Salvelinus alpinus) and Dolly Varden (S. malma malma) in the central Canadian Arctic

Two closely related but distinct species of char, Arctic Char (Salvelinus alpinus) and Dolly Varden (S. malma), are critically important to the food security and culture of Indigenous peoples in northern North America. Subsistence Inuit fishers in Kugluktuk, NU, Canada, have noticed changes in the timing and locations of their catches of char in the past ~ 10 years. In response, an ongoing partnered research program between the Kugluktuk Hunters and Trappers Organization (HTO) and scientists was formed to study Arctic Char and northern form Dolly Varden (S. malma malma). Char research near Kugluktuk presents a unique opportunity to further scientific understanding because the ecology and life history of sympatric populations of anadromous Arctic Char and Dolly Varden are not well-described, and anadromous individuals of both species inhabit the Coppermine River, NU. Additionally, Dolly Varden were conventionally understood to inhabit only systems west of the Mackenzie River, NT, where populations are listed as a Species of Special Concern under Canada’s Species at Risk Act (SARA), largely due to concerns regarding availability of spawning and overwintering habitats. Populations of Dolly Varden in Coronation Gulf have recently been described but nothing is known about their spawning and overwintering habitats. In Chapter 1, I used acoustic telemetry to document the summer marine movements of sympatric anadromous Arctic Char and Dolly Varden near the Coppermine River. Using network analysis, I investigated: 1) high-use areas of each species; 2) habitat types used by each species (estuary vs nearshore marine vs offshore marine); 3) minimum total distance travelled by each species; and, 4) inter- and intraspecific shared space use. I observed high-use of estuary and nearshore habitats by both Arctic Char and Dolly Varden. Dolly Varden used offshore habitats more than Arctic Char, although limited receiver coverage in the offshore marine environment likely did not capture the full extent of ii offshore travel. Minimum total distance travelled in each study year was similar between the two species. The median distance individual Arctic Char and Dolly Varden travelled per hour during their summer movements were 134 and 137 m, respectively. Arctic Char appeared to share space with other conspecifics more than expected by chance, whereas Arctic Char and Dolly Varden shared space less than expected by chance. Overall, it appears that these species occupy marine habitats differently. In Chapter 2, I used active tracking of radio-tagged fish to investigate potential spawning and overwintering locations used by Dolly Varden in the Coppermine River. I also deployed a radio receiver station to monitor the timing of movements as fish passed an obstacle (cascade) on their freshwater migration route. I found that Dolly Varden spawned and/or overwintered in the mainstem of the Coppermine River ~ 63-165 river km upstream of the ocean in riffle or run habitats. Fish that ascended the obstacle earlier were significantly more likely to travel a longer distance to their potential spawning and/or overwintering locations. The upper reaches of the Coppermine River appear to be important habitat for spawning and overwintering Dolly Varden. Together, my results can aid the development of species-specific restorative and stewardship measures and support the Kugluktuk HTO in protecting this critically important subsistence char fishery.

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