Abstract
Fish communities in the shallow (<1.5m) nearshore waters of the Walpole-Nornalup Estuary, on the south-coast of Western Australia, were sampled seasonally over a twelve month period using beach seine nets. Sampling was undertaken at a comprehensive range of sites throughout five regions of the system, during both day and night. Thirty-eight fish species from 24 families have been recorded, with the most abundant taxa being the atherinids Leptatherina presbytoides and L. wallacei, and the gobiid Favonigobius lateralis. The characteristics of the ichthyofauna differed substantially between regions of the estuary, seasons and between day and night. The lower regions of the estuary were dominated by marine spawning species (e.g. Arripis georgianus, Sillaginoides punctata and L. presbytoides), while the upper reaches contain a high proportion of solely estuarine species (e.g. Acanthopagrus butcheri, Afurcagobius suppositus and L. wallacei). Seasonal variation is most likely attributed to cyclic variation in physico-chemical water quality parameters, particularly salinity and temperature. Notably, abundances of the four gobiids Arenigobius bifrenatus, Pseudogobius olorum, A. suppositus and F. lateralis were far higher in summer than any other season.