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

Cutthroat trout historically had the broadest distribution of all trout species in North America. Of the 14 recognized subspecies of cutthroat trout, nearly all have been reduced to less than 5% of their native distribution since settlement by Europeans. Two subspecies are extinct, two subspecies are federally-protected as threatened, and several subspecies have been petitioned for protection under the ESA. Like most salmonids, cutthroat trout display a diversity of life history strategies. Although some cutthroat trout populations are anadromous, most are resident and display fluvial and adfluvial life histories. Cutthroat trout have declined across their distribution, but declines of adfluvial populations have been particularly dramatic. Not only are adfluvial populations susceptible to changes in stream and river habitats, but they must also contend with altered habitat conditions and nonnative fishes (i.e., predators, competitors) in lake systems. Adfluvial westslope cutthroat trout were once highly abundant in Lake Coeur d’Alene and its tributaries. However, changes in habitat conditions and fish assemblages have caused significant declines in their distribution and abundance in the basin. Recent efforts in tributaries of Lake Coeur d’Alene have focused on better understanding the distribution and movement dynamics of adfluvial cutthroat trout. Unfortunately, little is known about the age structure and growth of fishes moving from tributaries to Lake Coeur d’Alene. The purpose of this study is to evaluate the age structure and growth of outmigrating adfluvial cutthroat trout in tributaries of Lake Coeur d’Alene. Information on age structure and growth will greatly improve our understanding of cutthroat trout life history strategies in the system and thereby enhance the ability of land and fishery managers to better focus restoration efforts (e.g., habitat improvement activities, nonnative fish removal).