Spawning Habitat Selection of Sympatric Smallmouth Bass (Micropterus dolomieu) and Rock Bass (Ambloplites rupestris) in North Temperate Lakes: Habitat Separation in Space and Time

Abstract

Smallmouth bass and rock bass co-occur throughout much of their respective ranges and are believed to be ecologically similar. As a result, they are often placed into the same functional guild in ecological analyses, yet no such formal analysis of their relationship has been conducted. Smallmouth bass and rock bass clearly exhibit similar spawning behavior; both species spawn in shallow water in early spring and timing of spawning, along with similar habitat use could create competition between these two species, particularly when habitat is limiting. This study evaluated spatial and temporal overlap of spawning by sympatric smallmouth bass (Micropterus dolomieu) and rock bass (Ambloplites rupestris) in three north temperate lakes that have distinctly different littoral zone habitat compositions. The objectives of the study were to assess spawning habitat in relation to available habitat for smallmouth bass and rock bass and to assess the degree of spawning separation that occurred both spatially and temporally. Locations of smallmouth bass and rock bass nests in lakes were surveyed every other day during the spawning season using snorkel and SCUBA gear. Initial date of egg deposition was recorded for nests of both smallmouth bass and rock bass and nest site characteristics were then quantified. To assess habitat selection, logistic regression was used to compare sites where nests of each species were found relative to random sites in each lake. Linear discriminant analysis was used to assess degree of habitat overlap between smallmouth bass and rock bass nest use. The quantitative data from this study showed that spawning habitat selection by smallmouth bass and rock bass was similar; coarse substrates (sand and gravel) and wood or rock cover were selected by both species in all three study lakes. Smallmouth bass and rock bass were also found to overlap in the time they occupy nest sites (>50% in all three study lakes). Nest sites can be discriminated by how smallmouth bass and rock bass utilized similar microhabitat such as the placement of nests relative to cover and the amount of gravel substrate found in the nest. These results suggested smallmouth bass and rock bass can be placed in the same spawning guild for use in ecological analyses, yet show differences that allow both species to successfully coexist.