Preliminary analysis of ichthyoplankton assemblage structure in coastal, shelf and offshore waters of southwestern Australia

As part of the SFRME Biophysical Oceanography Program, this project is examining the structure and composition of ichthyoplankton assemblages in waters off Western Australia. Larvae are sampled using replicated oblique bongo net tows at three stations (18m, 40m, 100m depth) every month, and five stations (18m, 40m, 100m, 300m, 1000m) every quarter. The samples from the 355µm mesh nets are sorted to remove all larval fish which are then identified to family and species, where possible. Larval assemblages have been characterised, inter-seasonal and inter-annual trends identified, and related to dominant oceanographic and ecological processes. Samples from 18 months of cruises have been examined thus far, and larvae from 70 teleost families and approximately 160 species have been identified. Assemblages appear distinct between seasons at the inshore station (18m), and the two offshore stations (300m and 1000m), but the shelf stations (40m and 100m) show considerable variation throughout the year. Larval densities show peaks inshore in summer, and mid-shelf in autumn, and are possibly related to variation in strength of the Leeuwin and Capes Current, or climatic events. Additionally, preliminary correlations have been made with larval fish density and fluorescence peaks, and with the depth of the mixed layer on larval composition and abundance