Reproductive Success of Bull Trout Transported Over Mainstem Dams in the Clark Fork River Basin

Upstream migration of adfluvial bull trout Salvelinus confluentus populations in the lower Clark Fork River have been impacted by mainstem dams since as early as 1913.   In an effort to reconnect these migratory populations an upstream transport program was developed in 2001. From 2001 through 2010, a total of 315 adult bull trout have been passed upstream.  To verify the reproductive success of transported fish and learn more about bull trout life history characteristics a parentage study was initiated in 2008.  Fin tissue samples were taken from juvenile bull trout captured in two tributaries to the lower Clark Fork River over a three year period along with any adult bull trout captured in the study area including transported fish.  By comparing the genotypes of these fish using microsatellite markers we were able to assign juvenile fish to either one or both parents or determine if the parent was unknown.  Out of a total of 833 juvenile bull trout sampled over a two year period, 29.5 percent were assigned to at least one transport parent.  Additional information on size of spawning adults, consecutive versus alternate year spawning and number of mating pairs was also derived during this analysis.