Assessing Responses of Fish to Habitat Enhancement in Barrenlands Streams of the Northwest Territories

We examined the effectiveness of three fishpasses (two gabion-style pool–weir fishpasses and one nature-like choke-and-pool fishpass) at enhancing connectivity among three small, headwater lakes as part of a fish habitat compensation project in the Barrenlands region of the Northwest Territories. We quantified fish attraction and passage efficiency of fishpasses using PIT antennae, and compared fish use of fishpasses to reference streams using visual and electrofishing surveys for 1 year before and 2 years after their construction. We did not detect, observe, or capture any fish in either of the gabion-style pool–weir fishpasses during the first year after construction, and these two fishpasses were subsequently retrofitted to improve their hydraulic performance. After retrofits were completed, we still did not detect any tagged fish (≥150 mm) migrating through the two fishpasses using PIT telemetry, but identified some small fish moving downstream through these fishpasses during visual and electrofishing surveys. Conversely, we detected tagged Arctic Grayling Thymallus arcticus migrating upstream and downstream through the nature-like choke-and-pool fishpass during both postenhancement years, and also encountered fish throughout this fishpass during visual and electrofishing surveys. Compared with reference streams, gabion-weir fishpasses limited fish movement and use even after modification, whereas the nature-like fishpass successfully facilitated fish movement and use. We recommend against using gabion-style pool–weir fishpasses in Barrenlands headwater lake–stream systems, particularly when stream flow is limited, and suggest future projects aimed at enhancing lake–stream connectivity explore nature-like fishpass designs in an experimental management framework.