Restoration of Native Westslope Cutthroat Trout to an Isolated Stream System in Montana

Westslope cutthroat trout (WCT) are in decline range wide and in need of immediate conservation effort to protect remaining populations and restore populations in areas of extirpation. However, little is known about the relative importance of local adaptations and genetic diversity to long-term restoration success. In this study, embryos from five populations (3 wild, 2 hatchery) of WCT were introduced into >80 km of a protected stream system following the removal of nonnative species by piscicides. More than 26,000 individuals were introduced from 2006-2010 at multiple sites throughout the stream system. Survival, growth, movement, and reproductive success of each stock were monitored from 2007-2014 using genetic markers. Growth varied based on introduction site. Individuals introduced in a warm tributary grew more quickly and matured earlier than those introduced in a cold tributary. WCT filled available habitats below introduction sites within one generation. Movement patterns were directly related to stock of origin, with some stocks moving more readily downstream than others. WCT successfully reproduced in the first generation, and preliminary results based on genome sequencing suggest that one hatchery population had significantly greater reproductive success than all other stocks. Currently, the total population size is estimated to be over 15,000 individuals.