Fidelity and Survival of Juvenile Coho Salmon in Response to a Flood

We compared the movement and spring out‐migrant trap capture of 1,038 juvenile coho salmon Oncorhynchus kisutch tagged with passive integrated transponder (PIT) tags among four alcoves, seven backwaters, and six main‐channel pool habitats after a 5‐year flood. Sampling was conducted in November 1998 before the flood on 21 November and again in December, January, February, and March in selected habitat units. Along with out‐migrant trapping during spring 1999, these repeated sampling efforts were used to measure the fidelity of juvenile coho salmon to particular habitat units, the immigration of coho salmon into those habitat units, and out‐migration from them. Following the flood, fidelity and out‐migrant trap capture were greater for juvenile coho salmon occupying alcoves (50% and 17.0%) than for those occupying backwaters (16% and 6.1%) or main‐channel pools (7% and 2.7%). The out‐migrant trap capture of juvenile coho salmon that had been PIT‐tagged before the flood (16.1%; N = 209) was similar to that of fish PIT‐tagged after the flood (15.3%; N = 829). This study corroborates previous research on the benefits of off‐channel habitat to juvenile coho salmon and provides insight into the effects of flooding on these fish.