Long-term biennial patterns in Puget Sound Chinook salmon and Southern Resident killer whales: the role of pink salmon and implications for ecosystem management

This is the authors' abstract. We don't add key points for this paper.

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.