EXTENSIVE USE OF THE FRASER-RIVER BASIN AS WINTER HABITAT BY JUVENILE CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

Habitat in the low-water channel of the mainstem Fraser River and larger tributaries during winter may be an unappreciated factor influencing production of stream-type chinook salmon (Oncorhynchus tshawytscha) in this system. Data from electrofishing surveys showed that shorelines were used by juvenile chinook from river km 110 to km 770. Almost the entire mainstem was therefore probably winter habitat, and major tributaries such as the Thompson, Quesnel, and Nechako rivers were also used. Estimated chinook density on the mainstem Fraser increased with distance upstream (maximum 0.30 m-2 at km 750 (Prince George)), but the highest density (0.99 m-2) in the surveys was observed on the Thompson River at Spences Bridge. The mean size of juvenile chinook decreased with distance upstream on the Fraser, ranging from 97 mm at km 110 to 65 mm at km 770. Chinook juveniles were feeding on Diptera, Trichoptera, and Plecoptera in winter. Some apparent growth was observed in the lower Fraser in early winter.