Population Estimates of Northern Squawfish, Ptychocheilus oregonensis, at Bonneville Dam First Powerhouse, Columbia River

Northern squawfish, Ptychocheilus oregonensis, are well-known predators of juvenile salmonids in Pacific Northwest rivers and may substantially deplete the number of subyearling Chinook salmon passing Bonneville Dam. To assess predation impacts and evaluate management decisions, population estimates of northern squawfish are needed. Angling was used to derive a population estimate of northern squawfish in the Bonneville Dam First Powerhouse forebay pool during summer 1989. A crew of three to six fished from the forebay deck of the powerhouse with light sport-tackle and artificial lures. Between 5 and 19 July, a total of 2,464 adult northern squawfish were captured and 2,399 tagged. Tagged fish were recovered as early as the day after tagging; a total of 35 were recovered. The catch per unit of effort (CPUE) for the marking period averaged approximately 19 northern squawfish per hour. Nine additional tagged fish were recovered from 226 squawfish captured on 4 August. Three different statistical methods were applied to the catch data to provide population estimates of northern squawfish ranging from 54,480 to 61,828. 1994 NMFS (National Marine Fisheries Service) NWFSC (Northwest Fisheries Science Center) Library Public Domain 1861