Individual study: Elimination of fish resulted in an increase in density, survival, recruitment and population growth rates of cascades frog Rana cascadae in northern California
Pope K.L. (2008) Assessing changes in amphibian population dynamics following experimental manipulations of introduced fish. Conservation Biology, 22, 1572-1581
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Remove or control fish by catching
A replicated, controlled study in 2003–2006 of 16 lakes in northern California, USA (Pope 2008) found that cascades frog Rana cascadae density, survival, recruitment and population growth rate increased following elimination of fish. Initially, frog densities were similar in the 12 treatment lakes (2 frogs/100 m). However, following fish elimination, densities were significantly higher in removal lakes (frogs: 5–20/100 m; larvae: 12–40/100 m) than in fish stocked and stocking-suspended lakes (frogs: 2; larvae: 1–2). By 2006, there was no significant difference in frog densities in removal lakes and four existing fishless lakes. By 2006, survival estimates of frogs at removal lakes (94%) were higher than those in fishless (64%) and fish-containing lakes (75%). The same was true for population growth rates (removal: 1.7–3.0; fishless: 1.2–1.4; with fish: 0.9–1.2) and recruitment rates (removal: 0.8–1.8; fishless: 0.4–0.6; fish: 0.2–0.5). Twelve lakes were randomly assigned as fish-removal, stocking-suspended or continually stocked lakes. An additional four lakes were fishless. Trout were removed from autumn 2003 to spring 2004 with multiple, repeated sets of sinking gill nets. Frogs were surveyed in 2003 and every two weeks from June to September in 2004–2006. Visual encounter surveys of the shoreline and capture-mark-recapture surveys were undertaken.