Research Document 2024/063

Estimating Precautionary Approach Reference Points and Assessing Consequences of Harvest Control Rules for Fraser River Pink Salmon (Oncorhynchus gorbuscha)

By Glaser, D.M., Connors, B.M., Dionne, K., and Huang, A.M.

Abstract

Fraser River Pink Salmon spawn throughout the Fraser Basin in odd-numbered years and the Stock Management Unit is comprised of a single Conservation Unit. Landslides have occurred causing migratory impediments to returning adults at different periods with the most notable being Hells Gate in 1914 and more recently the Big Bar Landslide discovered in 2019. Fraser Pink Salmon marine survival is associated with sea-surface temperatures during early marine life, spring bloom timing, and the North Pacifc Current, all of which are expected to change as the North Pacifc warms as a result of climate change. Adult body size has declined over time, coincident with increasing abundances of salmon in the North Pacifc, which has the potential to impact reproductive output as fecundity scales with female size. We ft a state-space spawner-recruitment model to available data to characterize stock dynamics and derive estimates of biological reference points to assess stock status. We then developed a simple closed-loop simulation model based on recent estimates of productivity to quantify future expected biological and fshery performance of the current harvest control rule (HCR), an illustrative alternative HCR and a no fshing scenario. We estimated the proposed Upper Stock Reference (USR) point of 80% S_MSY to be 4.6 million (M) fsh (3.64-6.11M; median and 80th percentiles), the Limit Reference Point (LRP) S_gen to be 1.72M (1.10-2.70M), and the maximum removal reference rate (RR), U_MSY to be 0.56 (0.47-0.63). The most recent (2023) observed estimate of spawner abundance for Fraser Pink Salmon is 9.58M and we conclude that the Stock Management Unit is in a “healthy” state. The existing HCR for Fraser Pinks has a very low probability (< 5%) of the stock falling below its LRP, and a relatively high probability (87.5%) of spawner abundance being above the USR over the next 10 years. Assuming fsheries fully utilize allowable catch, median annual catch is projected to be 10.3M over the same time period. Assessment of an illustrative alternative HCR, which is strictly compliant with DFO’s Precautionary Approach Framework, had similar biological performance and slightly worse fshery performance. The results of a robustness test, where productivity was reduced to 10% of its recent estimate, showed that the current and alternate HCRs had a 9% and 20% chance, respectively, of the stock falling below its LRPs over the next 10 years. We conclude with recommendations on re-assessment triggers and potential areas to focus future work.

Research Document 2024/063 (PDF, 1,949 KB)

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