Trophic relationships between a native and a nonnative predator in a system of natural lakes

Abstract

Bull trout, a species of char listed as threatened under the US Endangered Species Act, have been displaced from portions of their historic range following the introduction of nonnative lake trout. It has been suggested that competitive exclusion as a result of trophic overlap between bull trout and lake trout may be the causal mechanism associated with displacement of bull trout. This study used stable isotope data to evaluate trophic relationships among native bull trout, nonnative lake trout and other fishes in seven lakes in Glacier National Park (GNP), Montana. Bull trout and lake trout had greater d 15 N values relative to other fishes among lakes (d 15 N ‡ 3.0&). Lake trout had greater d 15 N values relative to bull trout (d 15 N = +1.0&). Bull trout had greater d 13 C values relative to lake trout in six of the seven lakes examined. Although both bull trout and lake trout had greater d 15 N values relative to other fishes within lakes in GNP, differences in d 15 N and d 13 C between bull trout and lake trout suggest that they are consuming different prey species or similar prey species in different proportions. Therefore, displacement of bull trout as a direct result of complete overlap in food resource use is not anticipated unless diet shifts occur or food resources become limiting. Additionally, future studies should evaluate food habits to identify important prey species and sources of partial dietary overlap between bull trout and lake trout.

Food Web Interactions Associated With a Lahontan Cutthroat Trout Reintroduction Effort in an Alpine Lake

“…We sampled Speckled Dace and Lahontan Redside exclusively with minnow traps in littoral areas of Fallen Leaf Lake. Speckled Dace had relatively high d 13 C values indicative of a benthic-littoral dietary carbon source; similar trends have been observed in Lake Tahoe (Vander Zanden et al 2003) and oligotrophic lakes in Montana (Meeuwig et al 2011). Conversely, d 13 C values for Lahontan Redside were relatively low.…”

“…Mountain Whitefish and Kokanee had relatively low d 13 C values suggesting a planktonic or pelagic dietary carbon source; similar trends have been observed for these species in other oligotrophic lakes (Vander Zanden et al 2003;Meeuwig et al 2011). Terrestrial arthropods were present in the diets of both Mountain Whitefish and Kokanee, which suggests that the isotopic composition of one or both of these species may be a result of terrestrial sources.…”

“…Conversely, d 13 C values for Lahontan Redside were relatively low. Lahontan Redside exhibited a relative low d 13 C value compared to other fishes in a stable isotope analysis of Lake Tahoe fishes (Vander Zanden et al 2003), and Redside Shiner Richardsonius balteatus, a congeneric species, has been shown by Meeuwig et al (2011) to vary in d 13 C among lakes. Additionally, Lahontan Redside are opportunistic predators and may derive carbon from a variety of aquatic and terrestrial sources.…”

Stable isotope evaluation of population‐ and individual‐level diet variability in a large, oligotrophic lake with non‐native lake trout

“…), or indirect, via niche partitioning and competition with other predators (Donald & Alger ; Meeuwig et al. ). Over longer periods of time, the introduction of lake trout can cause trophic cascades (Tronstad et al.…”

“…Lake trout are apex predators (Ryder et al 1981) and introductions often cause conflicts with other sport fish and fishes of conservation concern (Ruzycki et al 2003;Quist & Hubert 2004;Martinez et al 2009;Syslo et al 2011). Conflicts may be direct, via predation (Eby et al 1995;Schoen et al 2012), or indirect, via niche partitioning and competition with other predators (Donald & Alger 1993;Meeuwig et al 2011). Over longer periods of time, the introduction of lake trout can cause trophic cascades (Tronstad et al 2010), especially in systems with introduced opossum shrimp Mysis diluviana (Bowles et al 1991;Ellis et al 2011).…”