Growth, condition, and environmental relationships in Atlantic cod (Gadus morhua) in the northern Gulf of St. Lawrence and implications for management strategies in the Northwest Atlantic

Northern Gulf of St. Lawrence Atlantic cod (Gadus morhua) is one of several stocks that collapsed in eastern Canada following a long period of intensi ve exploitation. Surplus and net production per capita became nil or negati ve in the mid-1980s so that any level of exploitation would have caused a d ecline of the stock. This was partly explained by a marked decline in growt h production and is consistent with smaller sizes-at-age but also lower con dition factor values during the same period. Correlations between size-at-a ge and temperature were not significant when corrected for autocorrelation, but slopes were always positive, suggesting higher growth rates at higher temperatures. Smaller sizes-at-age in the 1980s were not associated with ch anges in the fishery or increased fishing mortality, nor were they consiste nt with the density-dependence hypothesis. Lengths at age 8 decreased by mo re than 10 cm as the stock decreased 10-fold in abundance. While size-at-ag e and temperature covary in cod when all stocks are examined, size-temperat ure relationships are not as clear if the analysis is restricted to cold-wa ter stocks, possibly because of differences in food availability. Biologica l production varies from year to year and among stocks and should be taken into consideration when managing fisheries in variable or extreme environme nts.