Commercial Salmon Fisheries
Taku River Fishwheels - Coho Counts
Fish wheels on the Taku River are an essential platform for the coho salmon mark-recapture program, which provides inseason and postseason escapement estimates. Because fish wheel catchability can be affected by factors such as water level, fish size, abundance, daily spin time, etc., daily fish wheel catches do not necessarily have a meaningful relationship with upriver abundance. In 2018 fishwheel operation protocols were revised and now spin 18 hours a day instead of 24 hours.
Using the available stock assessment data for Taku River coho salmon, a bilateral estimate of inriver run size has been developed through SW 38-3. Through Tuesday, September 15 (Day 3, SW38), 5,997 fish have been examined for marks and 91 marks have been recovered. Assuming a sulk rate of 3 days, a total of 633 tags (this includes two tag removals — tags #39,732 and 39,829) were released through September 12 (Day 7, SW37). Applying these values to a Stratified Darroch yields an inriver run estimate of 44,028 (SE = 4,684) fish. Complete mixing (P=0.00) of tagged and untagged fish were significantly different but equal probability of capture (P=0.07) between release and recapture locations did not differ significantly. Expanding by the average run timing (78% through September 15) yields a projected inriver run estimate of 56,411 fish. An estimate of 4,550 Canadian-origin Taku River coho salmon have been harvested in the D11 US terminal drift gillnet fishery through SW38. Combining the projected inriver run estimate of 56,411 fish to the expanded D11 US terminal harvest of Canadian-origin Taku River coho salmon, generates a terminal run estimate of 62,500 coho salmon.
The current projected terminal run estimate of 62,500 fish is below the preseason forecast of 122,000 fish. The projected inriver run estimate of 56,411 is within the biological escapement goal range of 50,000 to 90,000 coho.