Habitat Selection by Smallmouth Bass in Response to Physical Characteristics in a Natural Stream

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Abstract
Habitat selection by smallmouth bass Micropterus dolomieui in shallow pools of the Flat River, Michigan [USA] during summer 1981 and 1982 was related to the distribution of substrate type, depth, and current velocities. When current velocity was increased through manipulation, smallmouth bass reduced time spent in a habitat, foraged less, and moved more. Manipulation of light intensity between sunlit and shaded habitats did not influence use of habitats by smallmouth bass. When smallmouth bass behavior and habitat choice were observed without habitat manipulation, the fish chose gravel- to boulder-sized substrate and they avoided sand and silt substrates. Areas deeper than 45 cm were preferred by Flat River smallmouth bass; however, preference for deep areas was directly related to fish length in 1982. Areas of reduced current velocity, generally less than 15 cm/s, also were preferred. Smallmouth bass spent much of their time in foraging-related activities; up to 40% of fish between 10 and 18 cm long were observed feeding in association with northern hog suckers Hypentelium nigricans. In contrast to laboratory experiments of habitat choice by smallmouth bass that lacked prey, Flat River smallmouth bass selected specific substrate types and were more active than fish in the laboratory, probably in response to prey distribution.