Retrospective Analysis of Atlantic Salmon Marine Growth Parameters in the Northwest Atlantic Based on Tag-Recovery Data

The life history of North American Atlantic salmon populations (Salmo salar) is characterized by extensive round-trip migrations between freshwater rearing habitats and marine feeding grounds off the coasts of Canada and Greenland. Low marine survival of postsmolts and immature adults is one factor causing population declines and preventing recovery of the endangered salmon populations in Maine, USA. Growth during the marine phase may be a biological constraint on survival and population trajectories. Retrospective analysis of historical marine growth patterns can provide insights into the causes for these declines in survival. The growth data we evaluated were obtained from a tag-recovery program conducted between 1966-1991 using hatchery-reared Atlantic salmon released as smolts in the Penobscot River. Information from recaptures of approximately 4,000 salmon at large for 1 month-3 years were analyzed. Length-weight measurements and time-at-large data were used to estimate von Bertalanffy growth parameters specific to the marine phase. We also examined variations in growth over time, and evaluated these variations in relation to oceanographic conditions in the North Atlantic. Determining the mechanisms that influence the growth and survival of individuals during the marine phase will elucidate the factors responsible for the significant declines and help guide future research and management efforts to facilitate recovery of the population.