UBC Theses and Dissertations
Density dependent catchability coefficient in the Georgia Strait salmon sport fishery Shardlow, Thomas Frost
This investigation examined the relationship between the catch per unit of effort (c/f) of salmon anglers and salmon abundance. The relationship was determined by using simultaneous estimates of both c/f and salmon abundance (n). Salmon in their natural marine environment were observed as they approached fishing gear. The components of catch, such as the number of fish approaching, attacking and biting the lure per unit of fished effort were video recorded. Salmon abundance was estimated simultaneously with catch and effort through the use of a chart recording echo sounder. The results showed that catch per unit of effort (c/f) was not linearly related to abundance (n) as in the simple expression: c/f = qn; where 'q', the catchability coefficient, is a constant proportion of the abundance caught by a nominal unit of fishing effort. In this study q was found not to be constant but to increase with abundance. This result contrasts with previous empirical studies of catchability in which estimates of q declined with fish abundance. However, because only historical catch records had been used to estimate catchability, few of the relevant details of the interaction between the fishing gear and fish were available. In the present study, video recordings of fish encounters with fishing gear suggest that feeding facilitation between salmon may be the mechanism underlying increcised catchability with abundance.
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