ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

Comparison of the size at entry into an estuary of marine spawned fish larvae of estuary dependent species

Tony Miskiewicz

Wollongong City Council, WOLLONGONG, AUSTRALIA

THEME: ASFB

Many species of fish along the east coast of Australia, which spawn in marine waters, use estuaries as juvenile nursery habitats. There are conflicting reports on the size at which marine spawned larvae of estuary dependent species enter estuaries. Some studies have concluded that larvae move into estuaries at sizes <10 mm while other studies report that movement into estuaries is by juveniles at a size of 10-30 mm. This paper reports on the results of a study that investigated the size range at which larvae and juveniles of a variety of estuary dependent species entered Lake Macquarie, a marine dominated estuarine lagoon on the east coast of Australia. Excluding elongate Clupeidae and Blenniidae, the majority of larvae of estuary dependent species caught on the flood tide were <12mm SL. This indicates that the majority of these species enter the estuary as larvae and not as juveniles. There were also interspecific differences in the size range at which larvae of individual species were caught entering the estuary. Larvae of Gobiidae, Ambassidae, Gerreidae and Monodactylidae, which are small as adults, were caught at smaller maximum sizes (<7mm) and were only caught in nearshore coastal waters off the estuary. Larvae of Sparidae, Girellidae, Terapontidae and Mugilidae, which are larger as adults, were caught at larger maximum sizes (10-14mm SL). Although larvae of these species were caught in nearshore waters, they were also caught further offshore. This indicates that these species spawn further offshore or that the larvae are spending a longer period in coastal waters, possibly surf zones, before entering the estuary.