Sockeye escapement estimation and ASL sampling for the Nuyakuk River, 2023

Executive Summary

The Bristol Bay Science and Research Institute (BBSRI) operated an adult salmon counting tower on each bank of the Nuyakuk River, Alaska in 2023. Data collected were used to estimate the age-specific adult sockeye salmon (Oncorhynchus nerka) escapement in the Nuyakuk River. Towers were located at the same locations in the lower Nuyakuk River as has been used historically by BBSRI and the Alaska Department of Fish and Game (ADF&G). These data were collected to reinitiate sockeye counts and conduct ASL sampling (age, sex, length) that will be used to update the historical brood table for this stock, assess the quality of Nushagak River sockeye escapement estimates, and support the broader assessment of aquatic resources with respect to the proposed Nuyakuk Hydroelectric Project (FERC No. P14783, Nushagak Cooperative (2023)).

Sockeye counts and ASL sampling followed protocols used by ADF&G (Brazil and Salomone, 2016) and ensured consistency with the historical data (annual counts of sockeye were counted from 1956 – 1988 and 1995 – 2002). In brief, staff counted salmon for 10 minutes of each hour from a tower on each riverbank; hourly passage was estimated by expanding the 10-minute counts six-fold and then summed for a total daily count. ASL samples were collected from sockeye captured with a purse seine. Beyond those fish, a number of sockeye were radio-tagged to support the Nushagak Cooperative’s migration and passage assessment for the Project Area.

Counts began on 27 June at 16:00 hrs and continued through 25 July at 23:59 hrs for a total of 29 days (Table 1). Of the 1,360 counting events, 82 (6%) of which had to be estimated due to poor visibility (rain or wind) or wildlife interference (bears in water or close to tower). The hours with a missed count were interpolated according to the standard method (for every hour missed, two hours prior and after were averaged). The operational termination date is determined as three days of counts that are less than 1% of the cumulative escapement, however the escapement was exceptionally high this year and resulted in needing less than 22,000 counted. We operated beyond the standard count objective for an additional five days to ensure the tail of the migration was included in the sample period. Daily escapement peaked on June 29 with 250,686 sockeye (Figure 1). Total escapement of sockeye to the Nuyakuk River was 2,303,748 for the counting period.

ASL samples totaled 543 and an additional 77 sockeye were radio-tagged. Digital data for this study was provided to the Nushagak Cooperative and Alaska Department of Fish and Game after final QAQC, analysis and reporting were complete.