Have recent mass mortalities of the sardine Sardinops sagax facilitated anexpansion in the distribution and abundance of the anchovy Engraulis australis in South Australia?

This paper examines the hypotheses (1) that Sardinops sagax and Engraulis a ustralis are spatially segregated and do not interact directly, and (2) tha t recent mass mortalities of S. sagax have facilitated an expansion in the distribution and abundance of E. australis. In South Australian waters, S, sagax and E. australis both spawn during summer and autumn. Eggs and larvae of both species occur over the continental shelf, and are abundant in area s where upwelling occurs (e.g, off the Coffin Bay Peninsula and the western tip of Kangaroo Island) and frontal systems form (e.g. in Investigator Str ait and the entrance of Spencer Gulf). Alter the mass mortality events in 1 995 and 1998, eggs and larvae of S. sagax were confined mainly to these are as, and estimates of the total abundance of S. sagax eggs and larvae in Sou th Australian waters fell by between 48 and 83% respectively. Between 1996 and 1999, densities of E. australis eggs and larvae increased in both key s pawning areas and the central and eastern Great Australian Bight, and total abundance of eggs and larvae increased by over 215 and 285% respectively. These results indicate that (1) S. sagax and E. australis are not spatially segregated and may interact directly, and (2) the mass mortalities of S. s agax may have facilitated an expansion in the distribution and abundance of E. australis. Hence, fluctuations in the relative abundance of S. sagax an d Engraulis spp. observed in the world's productive boundary current system s may also be possible in Australian waters.