A Petersen Mark-Recapture Estimate of the Steelhead Population of the Bulkley/Morice River Systems Upstream of Moricetown Canyon

The Bulkley/Morice river systems are important steelhead systems of the Skeena River watershed for which steelhead abundance has historically been estimated by indirect methods. In 1999-2000, a Petersen mark-recapture program was conducted to provide the first direct estimate of steelhead population in these rivers. Steelhead were tagged by seine and dip-net at Moricetown in Autumn, 1999, and an angling recapture program was conducted in Spring, 2000. The results of this project indicate the steelhead population upstream of Moricetown Canyon was 27,005 (95% confidence intervals 22,261-35,479) in Autumn, 1999. Classification of fish by sex was poor by the tagging crews during the Autumn fisheries. The seine and dip-net fisheries appear to representatively sample fish with respect to size, though there is some indication that they select different sizes. The rate of drop back of fish below the Canyon due to tagging is low. The tagged fish distribute themselves similar to untagged fish throughout the system. The Spring angling methodology appears to sample the fish population representatively with respect to sex, size, and tagged versus untagged. The derived population estimate appears to be an appropriate estimate based on its precision and the lack of significant violations of assumptions or demonstrable biases.