Moyle, Peter B. 1998. Effect of Invasive Fish Species on Freshwater and Estuarine Fishes in California. University of California -Davis

Effect of Invasive Fish Species on Freshwater and Estuarine Fishes in California

Freshwater and estuarine environments are among the most altered ecosystems in California, because they are subject to water diversions and intense human use. They are also among the most invaded ecosystems, especially by fishes. Of the 112 freshwater and estuarine fishes established in California, 54 are exotic species. About two-thirds of the native species are in serious decline. The linkage between the abundance of exotic species and the decline of native species is surprisingly poorly documented. While invading species have undoubtedly been responsible declines of native fishes, the invaded environments are typically already severely altered by human activity. Because invasion is a natural process (although not at the rate observed today), many native fishes seem to have the capacity to adjust to invaders. Populations of resident organisms may be reduced in response to a fish invader but extinctions that are solely the result of an invasion are surprisingly uncommon, at least in the time frames in which invasions have been studied. In California, such extinctions are most likely to occur when the successful invader is a top carnivore, when the invaded ecosystem has naturally low diversity, and/or when the native species have already been stressed by other factors. The role of invading piscivores has received particular attention in recent years including: (1) the Sacramento pikeminnow invasion of the Eel River, (2) the introduction and eradication of northern pike in two reservoirs, and (3) the proposed enhancement of striped bass populations. The pikeminnow example demonstrates that an invader can cause major alterations to fish communites. Although the prediction of such effects for northern pike has led to expensive eradication operations, the denial that such effects occur with striped bass (although they almost certainly do) has led to official proposals to greatly increase the number of striped bass in the wild. The contradictions and misunderstandings apparent in these examples indicate the need to for better public education on invasive species and need improve our predictive abilities of the effects of invasions.

Contact: Peter B. Moyle, University of California -Davis, Department of Wildlife, Fish and Conservation Biology, One Shields Avenue, Davis, CA 95616
Keywords: Ecological_interactions
Product Type: Publication, Proceedings
User Type: Resource_Management