Diel and tidal abundance of fish larvae in a barrier-estuary channel in New South Wales

Abstract

In four 24-h series of ichthyoplankton sampling during winter (June–July) 1996 in Swansea Channel (which connects Lake Macquarie with coastal waters of central New South Wales, Australia) 3367 fish larvae representing at least 77 species were collected. The larval fish community clustered by sampling date and by diel phase. Diel phase had a stronger influence on abundance of more common taxa than did tide phase, and also most influence on community structure. For most taxa there was no difference in abundance between flood and ebb tides, regardless of the estuarine or marine source of the eggs and larvae. All but two of 16 common species were present in Swansea Channel throughout their entire larval stage. The sparids Acanthopagrus australis and Rhabdosargus sarbawere present in the channel only at settlement-competent sizes. These two species showed evidence of selective presence in the channel during a particular diel or tidal phase, with A. australis apparently preferring night-flood tides, which would aid migration to the estuarine nursery habitats in Lake Macquarie. The ability or inclination to escape the strong bi-directional flows in channels seems limited to only a few taxa that appear to respond to physical cues and tidal current flows.