THE LARVAL FISH ASSEMBLAGE OF THE NORNALUP-WALPOLE ESTUARY, A PERMANENTLY OPEN ESTUARY ON THE SOUTHERN COAST OF WESTERN-AUSTRALIA

Fish larvae were sampled in the entrance channel and in the two basins of the permanently open Nornalup-Walpole Estuary, on the southern coa st of Western Australia, in each month between October 1989 and Septem ber 1990. Sampling yielded a total of 39 068 larvae belonging to 36 sp ecies and 23 families, with the engraulidid Engraulis australis (56.7% ) and the gobies Pseudogobius olorum (24.4%) and Favonigobius laterali s (15.0%) being the most abundant species. Most of the larvae were cau ght between November and March, with the concentrations of the most ab undant species reaching peaks between January and March, when water te mperatures had reached 21-24 degrees C. In terms of number of larvae, the larval fish assemblage in the basins was dominated by species that spawn within the estuary, with the larvae of these species contributi ng greater than or equal to 98.7% to the totals at the basin sites. Al though the larvae of 26 marine species were caught in the entrance cha nnel, these were either rare or absent in the basins, except for those of the terapontid Pelates sexlineatus, which were moderately abundant in the outer basin. The fact that the larvae of most of these marine species were at the preflexion stage, and that all but three of those species had never been previously recorded as either juveniles or adul ts within the system, indicates that they were passively transported f rom outside the estuary. The absence of larvae of most of the marine t eleosts that are abundant in the basins of the Nornalup-Walpole Estuar y parallels the situation in the nearby and seasonally closed Wilson i nlet.