Strontium:calcium ratios in Atlantic salmon (Salmo salar) otoliths and observations on growth and maturation

In this paper, we report on two data sets that have relevance to contemporary ideas on maturation in Atlantic salmon (Salmo salar): (i) an analysis of maturity fate of Atlantic salmon captured in the southern Labrador Sea and (ii) a study of otolith strontium:calcium ratios for maturing and immature Atlantic salmon. A discrimination function based on gonadosomatic indices was developed to classify maturation state of Atlantic salmon caught in Newfoundland and Labrador fisheries during the period 1985-1988. Atlantic salmon believed to be on feeding migrations were found to be in advanced states of sexual development. In an attempt to clarify the meaning of these data, chronological transects of Sr:Ca ratios from the otoliths of maturing and immature one-seawinter fish were collected. Sr:Ca ratios deposited during freshwater residency varied by stock and appeared to reflect the environmental availability of Sr. Sr:Ca ratios deposited during marine residency appeared to reflect somatic growth and sexual development. We detected no differences in the postsmolt Sr:Ca ratios for mature and immature Atlantic salmon from a hatchery stock originating in North America, suggesting that for this stock, little differentiation occurs between the maturity components. Mechanisms by which environment may contribute to the variation in maturation rate of North American Atlantic salmon are discussed.