Marine post-smolt growth and age at maturity of Atlantic salmon

The annual variation in sea-age of maturation for a hatchery dependent stock of Atlantic salmon was compared to variation in post-smelt growth as evidenced by circuli spacing patterns. The proportion of returns of 1-seawinter (1 SW) and 2 SW salmon and the fraction of the smelt year class or cohort that maturated as 1 SW fish, were compared to seasonal growth indices determined from circuli spacing on the scales of sm,lt class survivors returning as 1 SW and 2 SW spawners. Using image processing technique!;, we extracted inter-circuli distances from scales from 2244 recaptured fish. Spacing data for the first year at sea were collected and then expressed as seasonal growth indices for the spring period, when post-smelts first enter the ocean; the summer, when growth appears maximal; and winter, when growth appears to be al a minimum. In general, circuli spacings were wider for 1 SW than for the 2 SW returns of the same smelt cohort. The 1 SW fraction was significantly and positively correlated with late summer growth, suggesting that growth during this season is pivotal in determining the proportion of a smelt class that matures early. (C) 1996 The Fisheries Society of the British Isles