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To investigate environmental and seasonal patterns of mortality among natural populations of the blue mussel, Mytilus edulis, we transplanted 11 stocks of juvenile mussels to nine sites along the coast of Nova Scotia, Canada. Stock, Stock by Site, and Stock by Season together accounted for 53% of the variance in mortality whereas Site and Season together explained less than 1% of the variance. Genetic variability among stocks was inferred from differences in their cumulative mortality averaged over all environments. Several stocks, however, exhibited similar levels of mortality over all sites and were apparently insensitive to the environmental gradient. This implies physiological flexibility or the ability to tolerate a wide range of environmental conditions. We conclude that the blue mussel adapts to variable environments by maintaining both physiologically flexible and genetically variable populations. In addition, we noted that stocks originating from more stressful environments tended to exhibit lower mortalities than those originating from less stressful environments.

Abstract. The determinants of shellfish aquaculture production in Atlantic Canada are investigated through the estimation of Cobb‐Douglas production functions, relating production output to several independent input variables. The statistical analysis is carried out for both mussel and oyster culture, based on data collected in a survey of aquaculturists. For both production processes, capital investment and labour usage have a significant effect on production output. In addition, the level of managerial experience (estimated by the number of years in operation) plays a significant role in determining oyster production levels. Increasing returns to scale seem to exist for oyster culture techniques, while mussel culture exhibits constant returns to scale. Furthermore, our preliminary analysis suggests that from a private operator's perspective, labour usage on the average mussel farm is roughly optimal, while for the average oyster farm, an increased use of labour could be profitable. In contrast, for both mussel and oyster culture processes, there appears to be no economic incentive for increased capital investment.

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