Winter Habitat Use by Adult Largemouth Bass in the Pend Oreille River, Idaho

Abstract

We evaluated the behavior and use of overwintering habitat of adult largemouth bass Micropterus salmoides in the Pend Oreille River, Idaho, using radiotelemetry after increases in winter water levels. Largemouth bass tagged in late summer remained in backwaters until the initiation of the fall drawdown, when they moved to deeper shoreline areas. As water temperatures declined further, all but 1 of the 19 largemouth bass tagged throughout a 44.2-km-long section of river migrated to one of two overwintering areas. Once there, largemouth bass either showed no movement or migrated freely between the two overwintering areas. The overwintering areas were adjacent to the river, had an abundance of aquatic macrophytes, were more than 1 m deep, and had zero water velocity. Higher winter lake levels of 0.6 m did not attract wintering largemouth bass to backwaters. We hypothesized that habitat in overwintering areas was preferred because water temperatures there were several degrees warmer than in shallow backwaters.