Nushagak River Salmon Escapement Assessment:
Upper Nushagak and Koktuli Weirs, 2024 Annual Report

Executive Summary

In 2024, the Bristol Bay Science and Research Institute (BBSRI) successfully installed and operated two fish weirs as part of the Nushagak River Chinook Salmon Assessment Program. These weir projects produced escapement counts and age, sex, length and genetic data for adult Chinook (Oncorhynchus tshawytscha), chum (Oncorhynchus keta) and sockeye (Oncorhynchus nerka) salmon on the Upper Nushagak and Koktuli rivers. These data will provide points of comparison for the Chinook salmon escapement indices generated by the Portage Creek sonar project, operated by the Alaska Department of Fish and Game (ADF&G), and will form the foundation of an independent abundance index for the Nushagak River as the assessment program expands.

In 2022, the Alaska Board of Fisheries listed the Nushagak Chinook salmon as a stock of concern in response to dramatic declines in run sizes observed between 2010 – 2022. Nushagak River Chinook salmon returns have repeatedly failed to meet minimum sustainable escapement goals (SEGs) in the last six years and have proven difficult to comanage with abundant and commercially valuable sockeye salmon stocks. However, the system by which salmon passage in the Nushagak River is estimated, the Portage Creek sonar array, has been demonstrated to be inaccurate and highly variable when estimating passage for Chinook salmon (Data on file with Central Region Research Group, ADF&G, Division of Commercial Fisheries, Soldotna; Maxwell et al. 2020; Nass and Head 2024). Moreover, the escapement goal is based on unreliable sonar estimates and, therefore, may not be a realistic metric for Chinook salmon productivity in the Nushagak river system (Head and Hamazaki 2022). The Portage Creek sonar does not appear to be precise enough to inform regulatory decisions in low run years, yet Chinook salmon runs falling marginally below the lower SEG limits have prompted limitations of commercial sockeye salmon fishing opportunities in recent years (ADF&G 2025a; Sands 2023).

These challenges have highlighted the need for additional escapement monitoring efforts in the Nushagak River system, independent from the Portage Creek sonar. BBSRI began the Nushagak River Chinook Salmon Assessment Program in 2024 to provide better Chinook salmon passage data from major tributaries in the Nushagak River system, beginning with the installation of two fish counting weirs on the Upper Nushagak and Koktuli rivers. The program is intended to expand in the coming years, including the addition of mark-recapture and drone survey projects, with the ultimate goal of developing an independent Nushagak River Chinook salmon abundance index.

The Upper Nushagak weir operated from June 29 to August 12, 2024 with no outages, and the Koktuli weir operated from July 6 to August 6 with a seven-day outage from July 14 – 21. Passage counts of Pacific salmon migrating through the weir were conducted daily, and scale, sex, length and tissue samples were collected from Chinook, chum and sockeye salmon. The Upper Nushagak weir was operated for 44 consecutive days, and 2,206 Chinook, 7,259 chum and 1,369 sockeye salmon were counted during passage counts. Technicians sampled 174 (7.9%) of the Chinook, 186 (2.6%) of the chum and 99 (7.2%) of the sockeye salmon. The Koktuli weir operated for 24 days, and 966 Chinook, 5,940 chum and 2,166 sockeye salmon were counted. Eighty-seven (9.0%) of the Chinook, 196 (3.3%) of the chum, and 49 (2.3%) of the sockeye salmon were sampled at the Koktuli weir.

The Nushagak weir projects were funded through a Direct Legislative Grant from the State of Alaska.