Graduate Thesis Or Dissertation
 

Interactions between stocked trout and larval salamanders (Ambystoma macrodactylum) in high-elevation lakes

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  • The long-toed salamander (Ambystoma macrodactylum) is the top vertebrate predator in fishless high-elevation lakes in North Cascades National Park Service Complex (NOCA), Washington. The purpose of this research was to determine the effects of physico-chemical factors and introduced trout on abundance and behavior of A. macrodactylum larvae. Although high-elevation lakes in NOCA were naturally fishless, trout were stocked in many lakes during this century to provide recreational angling opportunity. Twenty fishless lakes and 25 lakes with fish were sampled from 1990 to 1994. Larval salamander density and behavior were assessed by snorkeling lake perimeters and searching through nearshore substrate material and aquatic vegetation. In fishless lakes, larval salamander densities were positively related to total Kjeldahl-N concentration (TKN) and negatively related to lake elevation. Based on analysis of salamander stomach contents, crustacean zooplankton, especially cladocerans, were important food resources for larval A. macrodactylum. Total crustacean zooplankton, as well as cladoceran densities, were positively related to TKN concentration, suggesting that increased zooplankton food resources contributed to increased densities of A. macrodactylum. The effects of fish introductions on larval salamander densities depended on TKN concentration and whether or not trout had established reproducing populations. Mean larval salamander densities for fishless lakes with TKN<0.05 mg/l, generated from a linear regression equation with TKN and lake elevation as independent variables, were not significantly different from mean larval densities in lakes with either reproducing trout or in lakes with non-reproducing trout. However, in fishless lakes with TKN≥0.05 mg/l, mean larval densities were significantly higher than in lakes with reproducing fish where trout reached high densities. In fishless lakes with TKN≥0.095 mg/l, mean larval densities were significantly higher than in lakes with non-reproducing fish where trout fry were periodically stocked at low densities. Reduced larval salamander densities in lakes with trout likely was a consequence of trout predation. Although most larvae were associated with boulder, cobble, and woody debris substrates in nearshore areas of NOCA lakes, differences in the proportion of larvae hidden in benthic substrates between lakes with fish and without fish were not statistically significant.
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