Author(s): Camrin D. Braun , Christoph A. Walser

Presentation: poster

Where introduced, largemouth bass are known to have negative effects on aquatic ecosystems. We used historical museum records (1942-2006) and contemporary (2009) collections to assess the distribution of largemouth bass in the lower Boise River. We also examined the stomach contents of largemouth bass collected during the contemporary survey to determine diet. Seventy-four largemouth bass were represented in thirteen historical collections from five lower Boise River locations. During autumn 2009, we sampled eight sites in the lower Boise River for largemouth bass. Sixty-one largemouth bass were captured from five sites downstream of a 4-m high diversion dam. Bass were absent from all sites upstream of the dam. Our contemporary collection data extends the known distribution of largemouth bass 7.2 river km upstream. The long-term persistence of largemouth bass in the lower Boise River indicates the fish may be spawning in the river and/or entering from external sources. Analysis of bass stomach contents revealed aquatic insects (40%), crayfish (37%), and small–bodied fishes (11%) comprised much of the diet. Our study confirms that the largemouth bass is successfully established in the lower Boise River. These findings suggest that bass could have a negative impact on native lower Boise River fishes.

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