Population Dynamics of Sergio mirim RODRIGUES 1971 Decapoda: Thalassinidea: Callianassidae in Cassino Beach, Southern Brazil

Abstract. Thalassinid shrimps have been extensively exploited for bait in many countries around the world. In order to prepare future management strategies for a little-exploited population of Sergio mirim in southern Brazil, growth, mortality and reproduction of this species were studied between June 1988 and November 1992. Size-frequency distributions were dominated by mature individuals, and recruitment occurred in austral spring, with widely variable abundances between years. Females attained larger mean and maximum sizes than males. The sex ratio was balanced for young individuals and female-biased for the mature segment of the population, as previously reported for other species of burrowing shrimps. Ovigerous females were found mostly between September and January, and egg numbers were a function of carapace length. From parameters of the VON BERTALANFFY growth curves, a maximum life span of approximately 4 years was estimated for both sexes. Among callianassids for which reproductive measures are known. S. mirim represents one of the highest reproductive potentials. The advantages of the thalassinidean female-biased sex ratio pattern is discussed.