Inriver Abundance of Copper River Chinook Salmon, a Comparison of Mark-Recapture and Sonar-Based Abundance Estimate Methods and Results

Utilizing two-sample mark-recapture techniques and research fishwheels for capture, the Native Village of Eyak Department of the Environment and Natural Resources (NVE-DENR) will estimate the annual inriver abundance of Copper River Chinook salmon such that the estimate is within 25% of the true value 95% of the time. Simultaneously, utilizing high resolution sonar at the Miles Lake sonar site, the Alaska Department of Fish and Game (ADF&G) will enumerate large Chinook salmon passage (fish measuring >750 mm total length) with separate funding. From 2022-2024, each inriver abundance estimate will be tracked independently inseason (running inseason estimate) and side-by-side postseason, with the goal of recommending a strategy for long-term population monitoring of Copper River Chinook salmon.

Long term monitoring of Chinook salmon escapement, inriver abundance, and total run size is critical data necessary for effective fishery management, especially under the current scenario of fully allocated Copper River Chinook salmon harvest with a population in an extended period of low abundance. Both federal and state managers depend upon the inriver abundance data which, combined with federal and state harvest data, can derive system-wide escapement and total returning run size to assess and modify preseason, inseason, and postseason Chinook salmon management. This data is required to maintain the subsistence allocation preference established in the Copper River Subsistence Salmon Fisheries Management plan (5 AAC 01.647). This project will also

assess the performance of the Miles Lake sonar at enumerating large Chinook salmon which, if reliable, could replace the mark-recapture process and enhance the quality of inseason data used by fishery managers.