Long‐term impacts of introduced flathead catfish on native ictalurids in a north Florida,USA, river

Introduction of flathead catfish, Pylodictis olivaris (Rafinesque), in waters of the USA has been widespread and often with negative impacts. Flathead catfish have been collected in Florida waters since the 1980s, and this study documents their impact on native fishes shortly after establishment. Four sites in the Choctawhatchee River, Florida, were sampled from 1997 to 2011, a time period spanning several years before and after the presence of flathead catfish at all sites. Flathead catfish expanded more than 91 river km in 2 years. The population increased rapidly and became the numerically dominant ictalurid at each site within 3 years of first detection at the site. Concurrent with the increases in flathead catfish was the precipitous decline of the native spotted bullhead, Ameiurus serracanthus (Yerger & Relyea). Electric fishing catch rates of flathead catfish significantly increased (P < 0.03) over time at all sites, while spotted bullhead catch rates significantly declined (P < 0.03) at three of four sites. Catch rates of flathead catfish and spotted bullhead were negatively correlated at all but the last site to be colonised by flathead catfish. This study provides evidence that introduced flathead catfish can quickly and significantly impact native ictalurids.