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8 I I I I I I I I I I I I I I I I I I I Dynamics of Northern Pike Spawning and Nursery Habitat in the Yampa River, Colorado Hill, Chris, and Eric Bergersen Colorado Cooperative Fish and Wildllfe Research Unit, Colorado State University. Fort Collins. CO 80523 Northern pike in the Yampa River are a major concern to fish managers in Colorado because of their potential threat to native fish and especially those listed as threatened or endangered species. Management of northern pike has been identified as a key step in the recovery efforts for the endangered fish of the region. One possible approach for managing northern pike is to limit their access to backwater spawning habitat and thereby reduce recruitment success. We evaluated the effectiveness of barriers as a possible management option for reducing recruitment. We evaluated different barrier materials, designs, and installation times as well as the likelihood of installing barriers on a large scale between Steamboat Springs and Craig, Colorado. Determining the effectiveness of barriers required that we document northern pike spawning times, the abundance and quality of spawning and nursery habitat, the possible effects of variable spring runofT on spawning and nursery habitat, and the success of recruitment. Collections of spawning adult pike in backwaters and water temperatures indicate that the primary spawning period takes place in the first two weeks of April. Potential backwater spawning habitat appears to be abundant in the Yampa River, but what we considered high quality backwaters are limited. Because pike spawn before the spring runoff begins the availability of spawning habitat appears to be consistent from year to year, but spring runoff can adversely affect nursery habitat if the backwater connects to the main channel. Relatively few young of the year northern pike were found in backwaters while limited sampling of off channel ponds indicate that these areas appear to be a more significant source for young of the year recruitment. Fall installation of barriers is not effective because of damage from ice during the winter. Spring installation is feasible but is limited to a very narrow window of time and is labor intensive. The reluctance of some land owners to allow barriers to be installed in backwaters on private property and the overall low recruitment found in backwaters suggest that the time and money spent on installation may not be worthwhile. Off channel ponds along the Yampa River are an important source of recruitment and should be the focus of future management. Escapement of adult pike from Catamount Reservoir into the Yampa River is a management concern that also needs to be addressed.