Patrolling males and waiting females: sex-specific reproductive movement patterns of black sea bream in oyster farming areas

Abstract The costs and benefits associated with reproduction differ between males and females, potentially leading to sex-specific movement patterns during spawning. In Hiroshima Bay, black sea bream Acanthopagrus schlegelii predominantly spawns in oyster farming areas (OFAs), where feeding and spawning sites spatially overlap. Because this species is likely an income breeder, males and females are expected to differ in their movement patterns within OFAs, reflecting sex-specific reproductive trade-offs during the spawning season. To examine this expectation, we used ultrasonic biotelemetry to track reproductively active individuals and analyse their horizontal and vertical movements. Males showed broader space use and more frequent vertical movements, especially in the evening, whereas females tended to stay near particular rafts with more localised movement and lower vertical activity. These sex-related differences in horizontal and vertical movement suggest more active mate-searching behaviour and higher spawning-related activity in males, whereas females show more spatially restricted movement while allocating energy to reproduction. Our findings provide the first field-based evidence of sex differences in reproductive behaviour among a typical broadcast-spawning sparid.