Composition, seasonality and distribution of the Ichthyoplankton in the Lower Swan Estuary, South-western Australia

Abstract

Paired conical nets (0.5 mm mesh) were used to sample ichthyoplankton at three sites in the lower Swan Estuary in each month between May 1986 and April 1987. In all, 3948 fish larvae were caught, representing 32 families and 60 species, of which 29 could be assigned species names. The Clupeidae (20.2%), Engraulididae (10.4%), Callionymidae (8.7%) and Nemipteridae (6.8%) made the greatest contributions to the total larval number, followed by the Pinguepididae (5.8%), Gobiidae (5.8%), Terapontidae (5.7%) and Monacanthidae (5.4%). The most numerous of the identified species were Engraulis australis (10.4%), Hyperlophus vittatus (8.9%), Callionymus goodladi (8.7%) and Sardinella lemuru (7.4%). The 11 most abundant of the identified species included 2 that spawn in the estuary (E. australis and Parablennius tasmanianus) and 2 that spawn at sea but are abundant as juveniles in the estuary (Pelates sexlineatus and H. vittatus). The remaining 7 species are not common as either juveniles or adults in any region of the Swan Estuary. The larvae of marine species collected just inside the estuary mouth were very similar in size to those collected a further 7.2 km upstream, indicating that they are transported rapidly through the lower estuary, presumably through tidal action. The concentrations of both eggs and larvae of all fish collectively, and the concentrations of larvae of most of the abundant identified species, peaked between late spring and midsummer (November- January).