Selection of Spawning Sites by Kokanees and Evaluation of Mitigative Spawning Channels in the Green River, Wyoming

Abstract

Abstract Selection of spawning sites by kokanees Oncorhynchus nerka was assessed over a 1-km reach of the Green River in the tailwater of Fontenelle Dam, Wyoming, during 1990 and 1991. Within this reach three spawning channels were constructed in 1990 to mitigate losses of spawning habitat that were believed to have resulted from extensive deposition of gravel and rubble in 1986. The channels were built through an island of gravel and rubble in the river channel. Kokanees selected certain water depths, current velocities, and substrate sizes for spawning, but these three variables were not sufficient to fully account for spawning site selection. The distribution of recently deposited gravel and rubble, and the presence of shallow riffles that discouraged entry to a spawning channel also influenced spawning site selection. The spawning channels provided a substantial portion of the spawning habitat used by kokanees during 1990 and 1991, but high spring flows in 1991 substantially altered the morphology of ...