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Northern Boundary Sockeye Run Reconstruction Model Review: Nass and Skeena Run Timing, 1982−2019

author Beveridge, I.A.; Alexander, R.F.; English, K.K.
published year 2023
document type technical report
species sockeye
location British Columbia
subjects run reconstruction, treaty, stock composition, escapement, harvest
access file download pdf

The Northern Boundary Sockeye Run Reconstruction (NBSRR) analysis is required for implementation of the 1999 Northern Boundary Sockeye Salmon (Oncorhynchus nerka) agreement of the Pacific Salmon Treaty (PST). The NBSRR analysis has been conducted annually since the mid-1990s to provide high quality and bilaterally agreed data on the Sockeye Salmon stock composition and aggregate escapement for five modelled stocks originating in the northern boundary area: Nass, Skeena, Stikine, McDonald Lake, and other southeast Alaskan stocks. The NBSRR model provides annual estimates of the total returns and harvests of Canadian and US Sockeye stocks in northern boundary fisheries required under the PST Sockeye annex and for monitoring trends in Sockeye Salmon returns to the Nass and Skeena rivers.

To assess potential shifts in mean aggregate run timing since 1982, we examined terminal run timing and timing of abundance and catch in fisheries over four periods: 1982−1989, 1990−1999, 2000−2009, and 2010−2019. The average run timing for Nass River Sockeye Salmon shifted later with each decade, while the average run timing by decade for Skeena River Sockeye Salmon remained relatively consistent over the four decades with 50% of the run passing the Tyee test fishery by 26 July. In Alaskan fisheries (i.e., Noyes and Tree Point), Nass Sockeye Salmon abundance timing has shifted earlier across the decadal intervals, with 50% of cumulative abundance moving from about statistical week 28 (1990−1999) to week 26 (2010−2019). In the terminal Nass marine fishery (Area 3D), timing of Nass Sockeye Salmon abundance has remained fairly consistent. The differences in run timing in Alaskan fisheries versus escapement in the most recent decade are likely related to the magnitude and timing of fisheries. More intensive fisheries early in the Nass Sockeye Salmon run and less intensive fisheries later in the run could account for the earlier run timing estimates for Nass Sockeye Salmon in Alaskan fisheries and later river entry timing in recent years. The timing of Skeena River Sockeye Salmon through Alaskan (Noyes and Tree Point) and terminal (Area 4Y) fisheries has remained nearly constant with little change in timing between the decades.