NWT RESEARCH DATABASE

Tags: mercury, water quality, fish habitat, hydrology, fish, water temperature

Objective(s): To describe the aquatic environment in the Yellowknife River between Bluefish Lake and Prosperous Lake.

Project Description: The multiyear monitoring programs at Bluefish accomplish the following objectives: • Monitoring effects to fish habitat from changes in water level and flow through Reach 1; • Monitoring of the seasonal use of Reach 1 and the Tailrace Area by spawning fish; • Monitoring of mercury concentration in large-bodied and small-bodied fish; • Continue winter investigations of egg incubation conditions and ice thickness; • Continue investigations of the effectiveness of spawning bed structures for egg incubation, and improve upon current structures; • Re-establish an unobstructed flow pathway through the in-stream flow release bypass (IFR) gate. Hydrology: Flow monitoring of the Yellowknife River between Bluefish Lake and Prosperous Lake will occur periodically and will co-inside with fisheries monitoring events. Flow will be measured by a flowmeter at the Flow Monitoring Station (FMS) located in lower Reach 1 of the Yellowknife River. To record water depth and temperature, two levelloggers will be installed at mid Reach 1 and lower Reach 1, upstream and downstream of the FMS. One barologger will be installed near the FMS to record barometric pressure. Flows will also be measured prior to and post-removal of a branch lodged against the Instream Flow Release (IFR) gate and will occur during the summer (July-August). Fisheries: Prior to conducting the fisheries field program, required fish permits will be obtained. The fisheries program consists of three components: fisheries monitoring, mercury special effects monitoring of large and small-bodied fish, and the continuation of the spawning bed pilot study. Supporting environmental information will be recorded for each day of the fish field program. This will include a description of the habitat, weather conditions (i.e., air temperature, wind direction, precipitation type, and percent cloud cover). Fisheries monitoring will be completed using snorkel survey methods and will focus on Reach 1 of the Bluefish Rapids in Yellowknife River and in Tailrace 1 and 2 (the Tailrace Area) at the northern end of Prosperous Lake. Snorkel surveys will be conducted from early September to mid-November and will be completed by a two-person crew. One crew member will recount visual encounters of fish species and eggs and enumeration estimates to the second crew member on the shore who will record data. Snorkel transect start and end points will be recorded with GPS points and snorkel durations will be noted. The mercury special effects monitoring programs will be conducted on small-bodied fish (slimy sculpin, Cottus cognatus) and large-bodied fish (northern pike, Esox lucius). Sampling events will take place in September and October. Fish will be collected in each of the inundated areas (the area between the old dam face and the new dam face), and within the Bluefish Lake upstream from the old dam (control). All fish collection methods will be timed, and location waypoints taken. A minimum of 20 slimy sculpin will be collected along the shoreline using a backpack electrofisher. Water quality data (temperature, pH, DO, conductivity) will be collected prior to each electrofishing effort. Up to 40 northern pike will be collected using fish collection methods that may include angling and/or short gillnet sets. Gillnet sets will not exceed 30 minutes. All target fish will be enumerated, measured to the nearest millimeter (mm), weighed to the nearest 0.01 gram (g) for small-bodied fish, and 1 gram for large-bodied fish (g). Slimy sculpin will be sealed whole in a clean plastic bag, and northern pike will be non-lethally (dermal plug) sampled and released. Any non-target species captured will be identified to species, enumerated, measured for length and weight, and released live. All samples will be kept frozen and sent to ALS for analysis. The 2017 spawning bed pilot study will expand to include the breadth of the lower Reach 1 bedrock-dominated spawning area. Expansion work will take place mid-summer (August), and will require a three-person crew. The expansion will be comprised of locally-sourced rock housed in wooden cribbing structures throughout the spawning area. The spawning beds will be constructed following guidance provided by Fisheries and Oceans Canada. The spawning beds located in lower Reach 1 will continue to be monitored for effectiveness. Assessments will be in conjunction with the fisheries monitoring snorkel surveys from September to mid-November and will follow the same methods described in that section. During each visit the entire area of the crib will be surveyed for spawning fish and egg survival. Water temperature and dissolved oxygen will be recorded at each subset of plots. Underwater photographs will be taken of egg densities with a ruler for scale. Winter investigations of egg incubation conditions and ice thickness will be conducted in mid and late winter. The 2018 Fisheries and Flow Monitoring Report will be provided to the Mackenzie Valley Land and Water Board for posting to the public registry. The fieldwork for this study will be conducted from August 10, 2018 to November 30, 2018.