Juvenile Chinook Salmon (Oncorhynchus tshawytscha) Utilization of Hawks Creek, a Small and Nonnatal Tributary of the Upper Fraser River

Hawks Creek, a small tributary of the upper Fraser River where there is no record of spawning salmonids, was examined from May to November 1990 for the presence of juvenile salmonids. Age 0+wild chinook salmon (Oncorhynchus tshawytscha) appeared in May, increased to peak densities of 0.76 fish∙m−2in late August, and were absent in November. Average residence time of marked chinook juveniles was 9 d. Duration of residency was size dependent, as small fish remained longer than large fish. Rainbow trout (Oncorhynchus mykiss) and mountain whitefish (Prosopium williamsoni) also had a short residency (mean = 21 d). We suggest that unsuitable rearing conditions (e.g., sediment load) in the mainstem Fraser River during the spring and summer favour the use of small, clear, and nonnatal tributaries by juvenile salmonids. Physical and biological explanations are proposed for their temporary use. These salmonid refuge habitats need to be protected.