Response of a fish assemblage to severe flooding in Gilmore Creek, a southeastern Minnesota trout stream

Abstract

Flooding in streams may result in the removal of fish or reduction in standing stocks. However, floods may also permit colonization by fish from sources downstream. Two extreme floods occurred over a 10-year period in Gilmore Creek, a trout stream in southeastern Minnesota. Both events were followed by temporary increases in fish species richness resulting from rapid incursions in 2004 by green sunfish (Lepomis cyanellus) and in 2007 by green sunfish and pumpkinseeds (Lepomis gibbosus), which probably moved at least 1.5 km from a lentic area downstream. After each flood event, sunfish declined by the following spring. Changes in the Gilmore Creek fish fauna were reflected in assessments of ecological health returned by one index of biotic integrity (IBI), with ratings declining from ‘good’ to ‘poor’ after each flood. Another IBI was less sensitive to the temporary increases in sunfish, although scores returned by the two IBI procedures were positively correlated.