EXAMINING RECRUITMENT RELATIONSHIPS FOR HECATE STRAIT ENGLISH SOLE (PLEURONECTES-VETULUS)

A conceptual framework was developed to examine recruitment relationships for English sole (Pleuronectes vetulus formerly Parophrys vetulus) in Hecate Strait, B.C. Canada. Response surface analysis was applied to data series for the 1946-1979 period with recruitment as the response variable and stock size, temperature and ocean transport as the independent variables. Three hypotheses involving the independent variables which could contribute to recruitment variation were investigated: 1. Hatching success and larval development and survival would vary with and have optima at an intermediate temperature; 2. Strong northward transport through Hecate Strait would carry larvae past suitable areas for settlement and would be a significant source of production loss; 3. Recruitment would be related to stock size and could be impaired at low stock levels, resulting in an asymptotic production curve. There was no support for an optimum temperature regime during the egg and larval stages from the results of this analysis but results did support hypotheses 2 and 3. A two-factor model incorporating effects of Ekman transport and stock abundance provided the best fit to the data. The relationship between year-class strength and Ekman transport was negative and asymptotic. Periods of high transport during the fall and winter were associated with years when weak recruitment was observed. Stock size accounted for more recruitment variation than any of the other factors examined. The form of the stock-recruitment relationship was asymptotic and recruitment was substantially reduced with stock abundance lower than approximately 30% of the virgin level.