Growth during the first summer at sea modulates sex-specific maturation schedule in Atlantic salmon

Recent decline in abundance of Atlantic salmon (Salmo salar) and concomitant changes in life history may result from a decline in the growth conditions during marine migration. Available literature suggests the existence of a sex-specific reaction norm linking maturation with environmental growth conditions at sea. However, the extent to which this mechanism explains variations in age at maturity remains unclear. Using a historical collection of scales (1987-2017) from the Selune River, France, we showed that marine growth declined over the first summer and remained stable during the subsequent periods at sea among returning salmon. Results support the hypothesis of a sex-specific probabilistic reaction norm, with individual probability to return after 1 year at sea increasing when growth increases. Females may require higher growth than males to attain their maturation threshold. This mechanism is a good candidate to explain temporal variability in sea-age at return at both the individual and population level in the Selune population and in many other southern European populations.

Automated summary

Recent research suggests that decline in Atlantic salmon abundance and changes in life history may be due to deteriorating growth conditions during marine migration. Analysis of historical scales from the Selune River in France shows that marine growth decreases in the first summer but remains stable in subsequent periods at sea. This supports the hypothesis of a sex-specific probabilistic reaction norm, where individual probability to return after 1 year at sea increases with growth. Female salmon may need higher growth rates than males to reach maturity, highlighting a potential mechanism for explaining variability in sea-age at return in the Selune population and elsewhere in southern Europe.