Reproductive biology, early life-history and settlement distribution of sand flathead (Platycephalus bassensis) in Tasmania

Abstract

The life-history ecology of P. bassensis was examined to determine the spatial and temporal patterns of spawning, larval transport and settlement distribution in coastal and continental shelf waters of southern and eastern Tasmania. Larval development is characterized by a large size at flexion and pelvic and dorsal fin formation, lightly pigmented trunk and tail and the absence of strong teeth on the roof of the mouth or lower jaw. The distribution of spawning fish and larvae and patterns of hydrography indicate that spawning occurs throughout estuaries, coastal embayments and inshore shelf waters of southern and eastern Tasmania. Larvae are concentrated in mid waters, which retain larvae inshore because cross-shelf subsurface currents are predominantly onshore. Spawning in P. bassensis occurred for up to six months between October and March. The broad range of lengths of 0+ fish in every month indicates that settlement occurred over an extended period, reflecting the protracted spawning period. Juveniles showed a preference for unvegetated habitats in nearshore waters, compared with beds of the seagrass Heterozostera tasmanica. Size compositions of 0+ fish indicate the presence of several cohorts in most months;this is discussed in terms of early life-history strategy and availability of settlement habitats.