Spatial and temporal patterns of size-at-sex-change in two exploited coastal fish

Fisheries are known to selectively remove larger and older individuals from wild populations. In sequential hermaphrodites, size-selectivity also becomes ‘sex-selectivity’, as the largest and oldest individuals of a sex-changing population primarily belong to one sex. Plasticity in size-at-sex-change is believed to circumvent the undesirable effects of gamete limitation and low effective population size. Here we present data of two commercially exploited sea bream species in different biogeographic regions, one protandrous (male-first) and one protogynous (female-first), respectively exhibiting spatial and temporal fluctuation in size-at-sex-change. By contrasting the patterns found against recent evidence of similar phenomena in other species, we discuss life-history strategies that favour reproductive success in different environmental scenarios. Size-at-sex-change may be for sequential hermaphrodites as important a life-history parameter as size-at-maturity or age-at-size. Consequently, the demographic consequences of altered size-at-sex-change should be considered explicitly in stock management and assessment.