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Habitat and diet differentiation by two strains of rainbow trout in Lake Superior based on archival tags, stable isotopes, and bioenergetics
Citation:
Negus, M. AND J. Hoffman. Habitat and diet differentiation by two strains of rainbow trout in Lake Superior based on archival tags, stable isotopes, and bioenergetics. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 39:578-590, (2013).
Impact/Purpose:
Ecological connections between the nearshore and offshore environments of a Great Lake are poorly understand, but provide a basis by which human caused impacts to nearshore coastal habitats may be propagated to the more physically distant offshore habitats. In this study, different types of tagging techniques were used to gage their relative ability to characterize movement and diet connections of rainbow trout, a key nearshore consumer, between the nearshore and offshore environments. We found that the two data sets highly complementary - tagging revealed that the fish is highly surface oriented, whereas the stable isotopes indicated that the fish was largely foraging in the nearshore environment. In concert, the data suggest that rainbow trout have a greater impact on nearshore prey fish populations than previously estimated, which suggests they may play an important role in energy exchange between the nearshore and offshore environmnents.
Description:
Two strains of potamodromous rainbow trout Oncorhynchus mykiss in the Minnesota waters of Lake Superior exhibited differences in behavior and temperature tolerance at egg and fry stages, but the extent of these differences was not well understood in adult fish. To gain a better understanding of their habitat use, archival tags that recorded time, temperature, and pressure were surgically implanted into the peritoneal cavities of both strains. Between 2006 and 2009, 34 steelhead ("STT") and 93 Kamloops ("KAM") bearing archival tags were released into Lake Superior. After the initial spawning season, 10 STT and 9 KAM tags were recovered after recording up to two years of data. Both strains were very surface-oriented, spending more than half of their time in the top 1m of water, and 80% of their time in the top 2m. Diel vertical movements were noted more often in STT, likely reflecting somewhat higher consumption of Mysis diluviana, while the frequencies of other vertical movement patterns were similar between the two strains. Mean temperatures recorded by tags were warmer than those used in earlier bioenergetics simulations of rainbow trout in Minnesota waters, and estimated consumption of prey fish by STT and KAM populations at the warmer temperatures was about 23% greater. Stable isotope analyses reflected higher consumption of small fish by both predator strains than identified in prior diet summaries based on stomach contents. Based on these analyses, the impact of both STT and KAM on prey fish populations in near-shore waters is greater than previously estimated.
