Northern Squawfish (Ptychocheilus oregonensis) Predation on Juvenile Salmonids in Sections of the Willamette River Basin, Oregon

Abstract

Predation by northern squawfish (Ptychocheilus oregonensis) on salmonids was studied in spring months in several lower, free-flowing areas of the Willamette River drainage, Oregon. During 1976 and 1977, 1127 northern squawfish were collected by electrofishing and seining, and examined for food contents. Almost 59% of the squawfish stomachs contained food items, but only 2% contained salmonids. Principal foods were insects, crayfish, and sculpins (Cottidae), and the majority (over 90%) of squawfish had not consumed more than one principal food type. We suggest that previous reports of squawfish predation in flowing rivers were misleading because they were often based on artificial situations (below dams or in waters following hatchery releases) which could have inflated salmonid predation values. Further, the true predatory nature of squawfish is clouded because of their rapid digestion of food and the long lag time in examination of gut contents by previous researchers. Our sampling techniques avoided these shortcomings by sampling in free-flowing areas and by examining squawfish stomach contents immediately after capture.Key words: squawfish, Ptychocheilus oregonensis; predation, food habits, Oregon