A preliminary report on juvenile chinook production in the Cowichan River during 1993 and 1994 / by J.R. Candy, D.A. Nagtegaal, and B. Riddell. : Fs97-4/2354E-PDF

"As part of an ongoing study to assess the productivity of chinook salmon (Oncorhynchus tshawytscha) in the Cowichan River, the Department of Fisheries and Oceans, Pacific Biological Station, began monitoring the downstream migration of chinook juveniles in 1991. Inclined-plane traps and auger traps were used in 1993 and 1994 to collect information on growth, abundance and migration timing. For both years, trap catch was expanded using two methods to give estimates of hatchery and naturally-spawned chinook migrants. The cross-sectional area method estimated 60-61% and the trap-efficiency method estimated 23-36% of known numbers of hatchery fish released above the trapping site. The production of naturally-spawned chinook juveniles was estimated at 350,000-430,000 in 1993 and 130,000-170,000 in 1994. The Cowichan hatchery released approximately 2.9 million juvenile chinook/year. Hatchery migrants tend to move downstream in a large pulse and most of the hatchery fish appeared in the estuary within a week after release"--Abstract, page vii.

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