Seasonal distribution, movements and habitat associations of northern squawfish in two Lower Columbia River reservoirs

Abstract

We tracked 335 northern squawfish implanted with radio transmitters in the Columbia River in May–December 1993 and May–September 1994. Most fish were released near The Dalles and John Day dams, with the remaining fish released into reservoir areas away from dams. We used boats with mounted Yagi antennas, fixed site receiver stations near the dams and aerial surveys to track movements of tagged northern squawfish. Northern squawfish were commonly associated with water <5 m deep, water velocities <1 m/s and were <45 m from shore. The average movement from the release site was 19.5 km; fish released near dams remained closer to their release sites than fish released into reservoirs. Short‐term movements (successive observations within 24 h) comprised 75% of all detected movements, represented fish moving short distances (mean=0.96 km) between dams and down‐river areas and corresponded to increased passage of juvenile salmonids. Long‐term movements (successive observations exceeding 24 h) were mainly attributed to fish released into the reservoirs moving up‐river to a dam, and fish moving between the two dam tailrace areas. A strong up‐river movement trend terminating at John Day Dam tailrace in June suggested that spawning occurred nearby. Reduced numbers of observations of fish in the autumn suggested that northern squawfish moved away from dam areas and into deeper water for the winter.