Breeding ecology, nest characteristics, and nest-site selection of stream- and lake-dwelling rock bass, Ambloplites rupestris (Rafinesque)

Abstract

This study examines the breeding ecology, nests, and nest-site selection of stream-dwelling rock bass, Ambloplites rupestris (Rafinesque), populating the Middle Thames River near London, Ontario. Breeding in this stream began earlier, at lower temperatures, and continued longer than in other documented lake-breeding populations. These responses were related to flooding which repeatedly thwarted breeding attempts. Nesting and spawning continued asynchronously throughout the seasons, increasing breeding opportunities. Older, larger males spawned earliest in the season, allowing them increased renesting opportunities. The duration of each stage in nesting and brood development was documented. Nests were generally larger than those of other rock bass populations. Male size and nest size were positively related. Nests were elliptical rather than circular as in lakes, reflecting the influence of water flow. Males demonstrated nest-site selection: individual nest sites were allocated nonrandomly with respect to depth, reflecting the availability of appropriate nesting substrates, and the majority of nests were constructed downstream from obstructions to current. Many of these features of rock bass reproduction can be interpreted as being responses to the relatively variable and rigorous environment of the stream habitat as compared with lakes.