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Long Term Effect of Rotenone Treatment on the Fish Community of Big Chico Creek, California.

Introduction

For more than 60 years rotenone and other piscicides have been used to remove non-game species of fish from streams. Treatments were based on the hypotheses that populations of game fish in the stream were limited by competition or predation from the non-game species. These hypotheses have been disputed for years by fish population ecologists (Hubbs, 1963: Becker, 1975; Moyle, 1975: Li, 1975: Kubicek and Price, 1976: Moyle, et al. 1983; Baltz and Moyle, 1984. Follow-up studies to piscicide treatment of open systems, while generally lax and often targeted more to angler usage than fish populations, have frquently concluded that after a few years the fish community was essentially the same as before treatment (Butler, 1975; Kubicek and Price, 1976; Moyle et al., 1983.)

The present study does not support either the hypotheses behind piscicide treatments or the conclusion that such treatments have only a short-term effect on native populations. Over the span of 10 years since treatment, populations of game fish are up slightly. However, they are up both in areas where non-game populations are comparable to pre-treatment populations and areas where non-game populations remain very low, so correlate better with a severe change in regulations (from a 10-trout limit to a zero-trout limit), than with changes in non-game populations.

The treatment had a substantial negative effect on biodiversity; several populations of native fish show negligible sign of recovering, while populations of all exotic species are up.

Organization

This report is organized as a web with active links between elements so the reader may proceed at will from one to the other: