Pink salmon returning from the Pacific Ocean have reached record-high abundances, leading to adverse effects on numerous marine species, including Chinook salmon. In Puget Sound, Washington, odd-year abundances of pink salmon spawners tripled after 1997; few return in even years. We used this extreme biennial pattern to search for corresponding patterns in natural-origin Chinook abundance and productivity that might also explain biennial mortality and births in Chinook-dependent Southern Resident killer whales (SRKW) that emerged during their decline after the 1997/1998 El Niño. In the Sultan River, Chinook spawners shifted upstream in odd-numbered years when sympatric pink salmon were abundant in the lower river and Chinook fry per redd declined. Since 1997, Puget Sound Chinook abundance averaged 34% less in odd- versus even-years, and was negatively correlated with pink abundance. These findings support the hypothesis that pink salmon reduced Chinook abundance and influenced the biennial patterns and decline of SRKW. Management actions to reduce the growing abundance of pink salmon, especially those reaching spawning grounds, could potentially benefit the recovery of ESA-listed Chinook salmon and SRKWs.

Sultan River Data

The Snohomish County PUD conducted spawning ground surveys to estimate spawning abundances of Chinook and pink salmon by river reach of each year, 1991-2022, using protocols developed by the Washington Department of Fish and Wildlife and Indian Tribes for rivers throughout the state (Smith and Castle 1994). Prior to 1991, only total river salmon counts were available.  Juvenile Chinook salmon emigrating from the Sultan River (primarily age 0) were enumerated using the protocol described by Murdock (2000) and Snohomish County PUD (2011).

Murdoch, A., Petersen, K., Miller, T., Tonseth, M., and Randolph, T. 2000. Freshwater production and emigration of juvenile spring chinook from the Chiwawa River in 1999. Prepared for: Public Utility District Number 1 of Chelan County. Wenatchee, WA.

Smith, C., and Castle, P. 1994. Puget Sound Chinook salmon (Oncorhynchus tshawytscha) escapement estimates and methods - 1991. Northwest Fishery Resource Bulletin Project Report Series No. 1. Washington Department of Fish and Wildlife, Olympia Washington.

Snohomish County PUD. 2011. Fisheries and habitat monitoring plan, Henry M. Jackson Hydroelectric Project with appendices. Everett, WA.

Puget Sound Chinook salmon data

Puget Sound escapements (spawners) and terminal runs (fish entering Puget Sound) of Pacific Salmon Commission Chinook Technical Committee wild Chinook salmon escapement indicator stocks.  Blank cells indicate no data available. The reported 1997 run for the Stillaguamish River (17,298 fish) was an extreme outlier and excluded from the analysis.

Data source:  Table B7 of PSC  2023. Pacific Salmon Commission Joint Chinook Technical Committee Report. Annual report of catch and escapement for 2022. Report TCChinook (23)-02. Annual values prior to 2009 were taken from the 2019 report. Available at www.psc.org.  

Puget Sound pink salmon data

Pink salmon escapement and runs to Puget Sound indicator watersheds and to all Puget Sound watersheds.

Primary data source: PFMC. 2023. Escapements to inland fisheries and spawning areas. Salmon review Appendix B. Pacific Fishery Management Council. Available at www.pcouncil.org. Escapement to the Green River provided by E Warner, Muckleshoot Indian Tribe. Prior to 1999, nearly zero pink salmon returned to the Green River. Blank cells indicate few if any pink salmon are present. Even year pink salmon values for the Snohomish watershed are from https://fortress.wa.gov/dfw/score/score/species/species.jsp