A version of this chapter appeared as: Tyler, T., W. J. L. Liss, L. Ganio, G. L. Larson, R. L. Hoffman, G. Lomnicky, and E. A. Deimling. 1998. Interaction between introduced trout and larval salamanders (Ambystoma macrodactylum) in high-elevation lakes. Conservation Biology 12:94-105.

ABSTRACT

The larval stage of the long-toed salamander (Ambystoma macrodactylum) is the top vertebrate predator in high-elevation fishless lakes in North Cascades National Park Service Complex, Washington, USA. Although most of these lakes were naturally fishless, trout have been stocked in many. The purpose of our research was to determine the effects of physico-chemical factors and introduced trout on abundance and behavior of A. macrodactylum larvae. Larval salamander densities were estimated by snorkeling. Snorkelers carefully searched through substrate materials within 2 m of the shoreline and recorded the number of larvae observed and whether larvae were hidden in benthic substrates. Physico-chemical factors were measured in each lake on the same day that snorkel surveys were conducted. In fishless lakes, larval salamander densities were positively related to total Kjeldahl-N concentration and negatively related to lake elevation. Crustacean zooplankton taxa, especially cladocerans, were important food resources for larval A. macrodactylum. Crustacean zooplankton and cladoceran densities were positively related to total Kjeldahl-N, suggesting that increased food resources contributed to increased densities of larval A. macrodactylum. Differences in larval salamander densities between fish and fishless lakes were related to total Kjeldahl-N concentrations and the reproductive status of trout. Mean larval salamander densities for fishless lakes with total Kjeldahl-N < 0.045 mg/l were not significantly different from mean larval densities in lakes with reproducing trout or in lakes with non-reproducing trout. However, in fishless lakes with total Kjeldahl-N 0.045 mg/l, mean larval densities were significantly higher than in lakes with reproducing trout where fish reached high densities. In fishless lakes with total Kjeldahl-N 0.095 mg/l, mean larval densities were significantly higher than in lakes with non-reproducing trout where trout fly were stocked at low densities. Reduced larval salamander densities in lakes with trout likely resulted from trout predation. There were no significant differences in the percentage of larvae hidden in benthic substrates between fishless lakes and lakes with fish. Our results imply that assessment of fish impacts on amphibians requires as understanding of natural abiotic and biotic factors and processes influencing amphibian distribution and abundance.