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 conte mporary ideas on maturation in Atlantic salmon (Salmo salar): (i) an a nalysis of maturity fate of Atlantic salmon captured in the southern L abrador Sea and (ii) a study of otolith strontium:calcium ratios for m aturing 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 migrat ions 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-seawint er fish were collected. Sr:Ca ratios deposited during freshwater resid ency varied by stock and appeared to reflect the environmental availab ility of Sr. Sr:Ca ratios deposited during marine residency appeared t o reflect somatic growth and sexual development. We detected no differ ences in the postsmolt Sr:Ca ratios for mature and immature Atlantic s almon from a hatchery stock originating in North America, suggesting t hat for this stock, little differentiation occurs between the maturity components. Mechanisms by which environment may contribute to the var iation in maturation rate of North American Atlantic salmon are discus sed.