TRENDS IN THE ABUNDANCE OF CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA) OF THE NECHAKO RIVER, BRITISH-COLUMBIA

Trends in abundance of chinook salmon (Oncorhynchus tshawytscha) of th e Nechako River, a tributary of the Fraser River, were analyzed to qua ntify the ecological effects of water abstraction for electricity gene ration. In years when the majority of returning chinook adults used th e upper Nechako River for spawning, the survival of offspring for the entire river was poorer than in years when spawning was concentrated i n the lower reaches. Relative to the historical discharge, the upper N echako River has experienced the greatest degree of water abstraction, and the lower survival of chinook broods originating from the upper r iver may be due to early emergence of fry caused by elevated fall and winter water temperatures or to higher rates of predation on juveniles and loss of rearing habitat caused by the elimination of the spring f reshet. Poor recruitment resulting from broods spawning predominately in the upper river has caused the trend in the abundance of Nechako Ri ver chinook to diverge from the trend of chinook populations of simila r life history from unregulated tributaries of the Fraser River. Addit ional reductions in flow may further affect the capacity of the upper Nechako River to produce chinook salmon.