Effects of aquatic habitat degradation on hybridization between two species of Sunfish: Bluegill (Lepomis macrochirus) and Green Sunfish (Lepomis cyanellus)

Abstract

Stream habitat degradation includes factors such as as increased turbidity and excessive sedimentation of the streambed resulting from surrounding urban land use and development. It is hypothesized that these two physical characteristics of streams have the greatest effect on hybridization of closely related fishes, leading to decreased biodiversity. The objective of this research was to determine if there is a correlation between substrate sedimentation, turbidity, and Hybrid Sunfish abundances. Hybridization between Bluegill (Lepomis macrochirus) and Green Sunfish (Lepomis cyanellus; an indicator of poor water quality), referred to as Hybrid Sunfish, was investigated. Additionally, species composition in degraded systems was investigated to determine if there is a relationship between habitat quality and Bluegill abundances. Four sections of the Olentangy River, near the Ohio State University, specifically within a reach of the stream that has recently been restored, were sampled a total of three times each using standard fish collection techniques. This yielded the sunfish species composition for each site. The Ohio EPA Qualitative Habitat Evaluation Index (QHEI) was used to determine quality scores for total habitat quality, and various habitat characteristics, within each of the four sections of the Olentangy River. Our data illustrates a negative correlation between the relative abundance of Hybrid Sunfish and total QHEI scores, substrate quality, quality and amount of available instream cover, and quality of pool habitat, suggesting that there are more hybrids in lower quality habitats. Furthermore, a positive correlation between the relative abundance of Bluegill and total QHEI scores, substrate, instream cover, and pool quality was found. These findings contribute to our current understanding of how degraded aquatic systems may affect biodiversity. They also support existing tolerance classifications for both Bluegill and Green Sunfish.