Suppression of Native Fish Populations by Green Sunfish in First-Order Streams of Piedmont North Carolina

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Abstract
The effects of introduced green sunfish Lepomis cyanellus on native fish communities in headwater streams of North Carolinaˈs Piedmont region were assessed from stream surveys and removal experiments. Green sunfish occurred in most first‐order tributaries; when they were present, their abundance and biomass almost always exceeded that of any other coexisting species. Green sunfish also occurred in all second‐ and third‐order streams surveyed, but they never dominated the fish community by numbers or weight in those situations. When green sunfish were removed from three first‐order streams, most native species increased in numbers and biomass; in two streams the increase more than made up (within 2 years) the biomass that had been lost by removing green sunfish. These removal experiments indicate that green sunfish suppress native fish populations in Piedmont headwaters. Predation on the young of other species is one likely means by which they do this. Received July 12, 1984 Accepted April 24, 1985