Complementation of habitats for Bonneville cutthroat trout in watersheds influenced by beavers, livestock, and drought

Multiple age-classes of Bonneville cutthroat trout Oncorhynchus clarkii utah throughout two Rocky Mountain watersheds were influenced by interactions among geomorphology, land use, activity by beavers Castor canadensis, and drought. Age-0 trout were present in a limited portion of the watersheds, and their distribution became increasingly restricted as drought conditions developed over a 3-year period. The Coal Creek watershed (including Huff Creek) produced the most age-0 trout in the first 2 years of the drought, lacked beaver activity, and was affected by land use, suggesting that spawning habitat was determined by geomorphology rather than land use or beaver activity. However, the high abundance of age-0 cutthroat trout in Huff Creek did not result in a high abundance of juvenile and older age-classes of fish in subsequent years, most likely because of the lack of complementary habitats providing refuge for older fish. A nearby watershed and its major stream, Water Canyon, had less spawning habitat and produced fewer age-0 fish during the first 2 years of the study but had more trout in the juvenile and adult age-classes, most likely because of a higher degree of habitat complementation. In Water Canyon, less-intense livestock grazing and the presence of beavers allowed for the development of pools and woody riparian vegetation that provided cover for older trout. Water Canyon was also the only stream to produce age-0 trout during the most severe year of drought, suggesting that streams with more natural habitat may provide a spawning refuge during low-flow conditions that occur periodically in the region. These results demonstrate that habitat complementation is important for the coexistence of multiple age-classes of fish and that the adjacency of spawning habitat and refugia is crucial for the persistence of fish in the face of environmental stress associated with drought.