Ecology and Control of the Columbia Squawfish in Northern Idaho Lakes

Columbia squawfish, Ptychocheilus oregonensis, and trout were found to occupy similar niches, resulting in competition for food and space, and predation on each other. Mature squawfish are piscivorous with food habits similar to Dolly Varden, Salvelinus malma, rainbow trout, Salmo gairdneri, and brown bullhead, Ictalurus nebulosus. Age and growth data are presented and in northern Idaho lakes a 13-year-old female squawfish attains a maximum weight of approximately 9 pounds. Males grow slower, averaging less than one half the size of the females. Spawning by lake populations occurs in lakes and streams. Lake spawning is in schools during late May and early June over wave-washed rubble on clear, calm days. The number of eggs in mature females varies from 12,000 to 100,000, averaging 40,000. Eggs hatch in 7 to 8 days. In six years of squawfish control in 3,800-acre Hayden Lake by dynamiting and gill netting spawning schools, mature squawfish were reduced to about one-tenth of their original abundance and an increase in trout noted.