Retrospective growth analysis of Atlantic salmon (Salmo salar) from the Miramichi River, Canada

We have developed a multidecadal retrospective growth history for the principal sea-age groups of the Miramichi River population of Atlantic salmon (Salmo salar) that characterizes freshwater growth and marine growth partitioned on a number of different time scales. Based on precedent with European salmon, we tested whether postsmolt growth was positively correlated with recruitment, assuming that growth during the postsmolt year mediates predation mortality. We found no such correlation in the Miramichi postsmolt growth pattern and instead found evidence of a negative correlation between growth and recruitment established by the second month that the fish were at sea. This negative correlation was interpreted as a density-dependant response of the population to recruitment determined early in the marine phase. There was inconsistent evidence that smolt size, as represented by freshwater zone length of the scale, influenced the pattern of recruitment. Finally, we found systematic differences between one-sea-winter (1SW) and 2SW returns related to greater postsmolt growth and, in particular, greater winter growth experienced by fish maturing after the first sea-winter. These data are consistent with findings relating climate variability during the months after smolts migrate to sea and recruitment variability, suggesting that the mortality is a short-duration event independent of growth conditions.