Residency, partial migration, and late egress of subadult Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) in Puget Sound, Washington

Abstract

Migratory behavior affects growth, survival, and fitness of individual fish, the dynamics and resilience of populations, and the ecosystems that fish occupy. Many salmonids are anadromous but individuals vary in the duration and spatial extent of marine migrations. We used telemetry to investigate movements of Chinook salmon (Oncorhynchus tshawytscha) that remained in Puget Sound (residents) rather than migrated to the Pacific Ocean. Most tagged Chinook salmon (26 of 37=70%) remained in Puget Sound for a substantial period, staying in the region where captured. However, 30% of tagged individuals, termed “transients,” subsequently left Puget Sound. Residents and transients did not differ in tagging date, body size, or origin (hatchery or wild). Compared with sympatric coho salmon (O. kisutch) where 80% remained as residents according to similar data, Chinook salmon tended to be detected closer to shore, in shallower water, and on fewer different receivers. For both species, residents showed limited movement within Puget Sound. We conclude that Chinook and coho salmon display resident and transient movement patterns across a behavioral continuum rather than within discrete migrational categories. These movement patterns are important because they affect the role of salmon in the ecosystem, their vulnerability to fisheries, and their accumulation of chemical contaminants.