Movement of larval fishes through the entrance channel of a seasonally open estuary in Western Australia

Abstract

Approximately 5300 fish larvae, representing 59 species and 39 families, were collected in flood and ebb tide samples taken by plankton and beach seine nets in the narrow entrance channel of a seasonally open estuary (Wilson Inlet), in the two to three months before the mouth became closed by a sand bar. All of the species were recorded on flood tides and eight of the nine that were also found in ebb tides were spawned within the estuary. The other 51 species belonged to teleosts which typically breed at sea. The most abundant species caught during this study (Favonigobius lateralis) was flushed out of the estuary as preflexion larvae on ebb tides and then re-recruited as postflexion larvae on flood tides. While other species which spawn within the estuary (e.g. Pseudogobius olorum, Engraulis australis and Urocampus carinirostris) were also flushed out on ebb tides, they rarely returned on flood tides as postflexion larvae. Of the 51 marine species, 35 were not collected as either juveniles or adults within the estuary. These species were caught only on flood tides and mainly as preflexion larvae. In contrast, the sparids Pagrus auratus and Rhabdosargus sarba, which occur as juveniles in the estuary, were found entering the entrance channel on flood tides as postflexion larvae. The fact that the last two species are amongst the few teleosts that might be recruited as larvae into the main body of the estuary, reflects the very small tidal movement in that part of the system.