Fish community structure associated with stabilized and unstabilized shoreline habitats, Coeur d'Alene River, Idaho, USA

ABSTRACT Stabilization of riverbanks and lake shorelines has become widely used to reduce erosion. Studies on effects of stabilization on fish species and communities have indicated highly variable effects from beneficial to detrimental. Bank stabilization implemented to reduce shoreline erosion of metals‐contaminated sediments in the lower Coeur d'Alene River, Idaho, prompted concern of possible effects on the fish community. Fish sampling (electrofishing and gillnetting) and habitat assessment were conducted at 24 sites in the lower 54 km of river during 2005 and 2006 to assess differences in the fish community (relative abundance, species diversity and community composition) at stabilized and unstabilized shorelines. Within stabilized and unstabilized shorelines we evaluated seasonal differences as well as upstream and downstream differences. We captured 3511 fish from 17 species and 7 families; 83% of fish were captured by electrofishing. Fish relative abundance was significantly higher at stabilized than unstabilized sites for electrofishing. We also found positive correlations between relative abundance and diameter of rock at stabilized sites for both sampling gears. Three species (brown bullhead Ameiurus nebulosus, northern pike Esox lucius and pumpkinseed Lepomis gibbosus) were captured more readily at stabilized shoreline sites. Seasonally, the differences in relative abundance among habitat types indicate that stabilized structures are providing stable habitat year‐round. Overall, stabilized shorelines on the lower Coeur d'Alene River were not found to be adversely affecting overall fish relative abundance, diversity and species composition under the existing low fraction (2.5%) of bank stabilization. Based on these results and reviews of other studies, we suggest that two factors affecting the results of bank stabilization studies are (i) the habitat quality of the unstabilized river, and (ii) the percentage of the river that has been stabilized. Copyright © 2010 John Wiley & Sons, Ltd.