Removal of an Exotic Fish Influences Amphibian Breeding Site Selection

For pond-breeding species, the distribution of larvae is a reflection of habitat suitability and adult breeding site selection. Some species preferentially breed in ephemeral ponds, which can provide benefits for larvae. An alternative strategy used by adults to increase offspring survival is to detect aquatic predators and avoid them when selecting breeding sites. We investigated whether either of these types of breeding site selection are contributing to the negative correlation between the distributions of tadpoles of the threatened green and golden bell frog (Litoria aurea) and the introduced eastern gambusia (Gambusia holbrooki) in Sydney, Australia. From 2003 to 2012 we drained ponds to temporarily remove gambusia and examined the effect of removal on the numbers of male, female, and juvenile frogs, and tadpoles. We found that males preferentially selected fish-free ponds as breeding sites. In addition, the removal of gambusia increased tadpole abundance to over 140 times that of an undrained pond. Pond draining did not influence female or juvenile abundances. The ability to detect and avoid gambusia may be mitigating the effect of predation to a certain extent. We conclude that pond draining to remove exotic fish is an effective strategy that can be used to greatly increase the reproductive success of this and potentially other threatened amphibian species in the presence of exotic predators.