| Summary: | 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. === Graduation date: 1997
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