Growth patterns in postsmolts and the nature of the marine juvenile nursery for Atlantic salmon, Salmo salar

We examined scale samples from historical collections of postsmolts from the Gulf of St. Lawrence, Canada, with the aim of understanding the role of estuarine and coastal habitats as a juvenile nursery for Atlantic salmon. Circuli spacing patterns were extracted from the scales of 580 postsmolts collected in the Gulf during three seasons, 1982-84. Poststratification of the samples by collection date within year suggests that in some years postsmolts remain in the Gulf throughout the entire summer growth season, whereas in other years only slower growing fish remain in these areas. Growth patterns for Gulf of St. Lawrence postsmolts were compared with patterns for returns from three salmon stocks from the southern end of the range in North America. These data suggest that in some years postsmolt growth in the Gulf is as robust as that observed for both the one seawinter (1SW) and two seawinter (2SW) returns to southern rivers. Postsmolts are believed to use oceanic nursery areas generally; thus, comparable growth between the two stock groups suggests that the Gulf may serve as an important part of the postsmolt nursery range in some years. The concept of the postsmolt nursery as a continuum between neritic and oceanic areas is essential to evaluating ocean climate and productivity effects on salmonid recruitment.