Retrospective analysis of marine growth and relationships to return rates of Penobscot River Atlantic salmon

Beginning in the 1980s, return rates of Atlantic salmon (Salmo salar) to the Penobscot River, Maine, USA, declined and have persisted at low levels. This downturn coincided with similar declines in North American and European Atlantic salmon stocks and with changes in the Northwest Atlantic ecosystem. Previous studies investigated whether early marine growth explained the declines, but results varied, with decreased growth associated with declines in European stocks but not North American stocks. In this study, we evaluate whether growth over the entire marine stage is related to Atlantic salmon marine survival. We constructed a growth time series from scales of returned Penobscot River Atlantic salmon spanning periods of varying marine survival. We used analysis of variance (ANOVA) and post hoc tests to quantify seasonal growth increment differences and principal component analysis to characterize variability among the suite of growth increments. We observed reduced growth during the second winter and second marine year starting in the 1990s, with com-pensatory seasonal growth relationships. These results indicate that diminished growth during late marine stages is associ-ated with low return rates in this population.

Automated summary

This study aims to evaluate the relationship between growth during the entire marine stage and marine survival of Atlantic salmon. The results showed that growth of Penobscot River Atlantic salmon decreased during the second winter and second marine year starting in the 1990s, but compensatory growth relationships were observed. This indicates that diminished growth during late marine stages is associated with low return rates in this population.