Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

Despite considerable research over the last 60 years, numerous questions remain regarding appropriate management of kokanee Oncorhynchus nerka in Idaho. For instance, kokanee suffered significant declines in the late 1960s in Lake Pend Oreille, but the exact cause(s) have not been identified. Similar declines have been described throughout the western United States and Canada. Numerous hypotheses have been posited as causing kokanee declines in Idaho; namely water development, the introduction of opossum shrimp Mysis diluviana, predation, and exploitation. In an effort to supplement or maintain kokanee populations, the Idaho Department of Fish and Game (IDFG) has instituted large-scale hatchery supplementation of the species. However, the success of hatchery supplementation in Idaho is varied, necessitating a better understanding of the ecology of kokanee and the comparative success of different breeding groups (e.g., early-run, late-run). Underlying research questions associated with understanding the management of kokanee in Idaho is the need to address uncertainty surrounding common sampling techniques (e.g., mid-water trawls, hydroacoustics). Therefore, the goals of the research are to 1) evaluate the biases of mid-water trawling, 2) investigate interspecific competition between mysids and kokanee, and 3) evaluate the performance of kokanee breeding groups (early-run, late-run) in Idaho.