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Grand Teton National Park Report

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Across their range, native salmonid species are imperiled due to habitat loss, alteration, and competition with non-native salmonids. New challenges, such as the effects of climate change on stream flow and water temperature create new problems for these species and highlight the importance of understanding their juvenile and adult life histories. Specifically, identifying life history movement patterns as it relates to spawning sites and juvenile rearing streams. We measured strontium isotope values of 13 tributaries and mainstem waters of the lower Snake River and Jackson Lake as well as otoliths collected from resident/juvenile cutthroat trout to determine if we could find unique isotopic signatures throughout the watershed. Strontium isotope values were similar for otoliths and water samples collected at the same location. Strontium isotope yielded unique isotope values across the watershed and between tributaries and the Snake River and Jackson Lake. Only three tributaries were undifferentiated using strontium stable isotopes. These were Pilgrim, Dime, and Sheffield Creeks. Due to their close proximity geographically and their geologic similarities it is not surprising we were unable to differentiate these three tributaries from each other. Future work using trace element analysis might provide further differentiation between these three creeks. Using this new information, we can now begin to look at adult cutthroat from Jackson Lake and the Snake River and determine their natal origins and fidelity to spawning tributaries. Using this information, managers can guide conservation efforts for cutthroat trout in the Jackson Lake watershed.