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Providing evidence to improve practice

Individual study: Removal of non-native fish results in population expansion of mountain yellow-legged frog Rana muscosa in the John Muir Wilderness (Sierra National Forest) and Kings Canyon National Park, California, USA

Published source details

Knapp R.A., Boiano D.M. & Vredenburg V.T. (2007) Removal of nonnative fish results in population expansion of a declining amphibian (mountain yellow-legged frog, Rana muscosa). Biological Conservation, 135, 11-20


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Remove or control fish by catching Amphibian Conservation

A replicated, before-and-after study in 1996–2005 in six lakes in California, USA (Knapp, Boiano & Vredenburg 2007) found that mountain yellow-legged frog Rana muscosa densities increased significantly following predatory fish removal. In three lakes, densities increased significantly from the first five (1996–2002) to last five surveys (2004–2005) for tadpoles (0–12 to 4–91/10 m) and frogs (1–2 to 24–29). Increases were significantly greater than in fishless control lakes for tadpoles (+35 vs +2) and frogs (+25 vs +1). Within 1–3 years of starting fish control, frogs were detected in three lakes where they were previously absent (frogs: 3–67; tadpoles: 0). Complete eradication of fish was achieved from three lakes within 3–4 years, in the other three small numbers remained because of connecting streams. Non-native trout (Oncorhynchus sp., Salmo sp., Salvelinus sp.) were removed using 3–13 sinking gill nets (36 m long x 1.8 m high) set continuously in each lake. Netting was continued until catch rates fell to zero for an entire summer. Fish were eliminated from connecting streams when they dried out, using gill nets and electro-fishing. Frogs and tadpoles were recorded using visual surveys of lake perimeters before and 1–6 times after fish eradication started, up until 2005.