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


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.


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