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Providing evidence to improve practice

Individual study: Reproductive success of California red-legged frogs increased significantly following elimination of non-native fish in California

Published source details

Alvarez J.A., Dunn C. & Zuur A.F. (2002) Response of California red-legged frogs to removal of non-native fish. Transactions of the western section of the Wildlife Society, 38/39, 9-12


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Remove or control fish by drying out ponds Amphibian Conservation

A replicated, before-and-after study in 1998–2003 of seven ponds in California, USA (Alvarez, Dunn & Zuur 2002/2003) found that the reproductive success of California red-legged frogs Rana draytonii increased significantly following elimination of non-native fish by pond drying. Adult numbers were similar after fish elimination (0–40 to 1–41/pond), but juveniles increased significantly (0–15 to 1–650). Fish were eliminated during the first draining, or for two ponds with mosquitofish Gambusia affinis on the second draining. Seven ponds were drained in autumn in 1998–2001. Pumps were used to drain the water to a depth of 50 cm and then below 3 cm. Seines, throw nets and dip nets were used to remove all fish. Mud was smoothed and a small amount of household bleach applied to eliminate mosquitofish. Ponds were filled from ground water springs. Red-legged frogs and fish were surveyed six times per year in 1998–2001.