Investigating occupancy, habitat use, and migrations of Arctic Grayling (Thymallus arcticus) in northern barrenland streams

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The Gahcho Kué Project is a diamond mine development located approximately 280 km northeast of Yellowknife, NT, near a small headwater lake, Kennady Lake. A large portion of Kennady Lake will be dewatered to access diamond-bearing kimberlite pipes under the lake. Kennady Lake supports several northern fish species, including Arctic Grayling (Thymallus arcticus) - a species of cultural and subsistence significance to Aboriginal fishers, and a popular sport fish. Stream habitats downstream of Kennady Lake are used by Arctic Grayling for spawning and rearing, and will likely be affected by reductions in flows after the dewatering of Kennady Lake. To mitigate effects of the Project on stream habitats used by Grayling, De Beers developed a flow augmentation plan. There is considerable uncertainty as to whether this plan will be effective because we have a poor understanding of Arctic Grayling migrations and habitat use in the watershed, and because entrenched methods of collecting baseline data often do not allow for robust assessments in future years. Our research includes two complementary components. Results from an acoustic telemetry study will provide insight into the timing and directionality of Arctic Grayling migrations, address the suitability of proposed mitigation flows, and inform the design of models used to assess Grayling habitat use (habitat occupancy models). Development of habitat occupancy models will allow quantification and comparison of Grayling habitat use in affected and unaffected watersheds, before and after dewatering. Results from this research program will facilitate robust assessments and predictions of how habitat use by Arctic Grayling changes in response to development and mitigation actions. Results will enable De Beers to implement an adaptive management plan that maximizes the effectiveness of their mitigative actions, and to design and employ an efficient, effective, and scientifically defensible monitoring plan. Outcomes will also include a methodological template that can be transferred to other mining operations.