Fecundity peaks prior to sex transition in a protogynous marine batch spawning fish, black sea bass (Centropristis striata)

Abstract

Abstract Understanding the dynamic processes that contribute to reproductive output is vital to determine appropriate harvest controls and sustain marine fisheries. For sequential hermaphrodites, the process of reproduction is complicated by sex transition within the life history. We examined the reproductive dynamics of black sea bass (Centropristis striata), a protogynous serranid, within a major fishing region of the Northwest Atlantic during two consecutive spawning seasons to quantify the strength of size-dependence and the magnitude of temporal variation in several key traits. Specifically, we estimated the size-dependence of sex ratio, maturity, spawning capability, batch fecundity, and spawning frequency at both fine (weeks/months) and broad (years) temporal scales. We observed fecundity to be highest in females of intermediate body size, which was entirely a function of reduced spawning frequency among the largest females. Female fecundity peaked at sizes well below the estimated size at sex transition, and contrary to the pattern typically observed for gonochoristic fishes in which the largest females yield the greatest number of eggs. Among protogynous fishes, females may decrease egg production prior to sex change and instead allocate energy to somatic growth, benefitting from larger body size during the subsequent male phase. The production of fewer batches of eggs by larger females directly impacted estimates of annual fecundity. In addition, we detected large interannual differences in the proportion of spawning capable females, and also spawning frequency, which resulted in considerable variation between annual fecundity estimates. The inclusion of temporal and size-dependent variation in female egg production should produce more robust estimates of stock reproductive potential and its response to changing harvest scenarios.