Non Technical Summary

Glass eels were sampled from the Hacking River catchment from May 1998 to June 2000 in order to determine seasonal recruitment patterns of the two local eel species. River eels spawn in the ocean. Fertilized eggs develop into leptocephalus larvae, which drift in the ocean for over 200 days before metamorphosing into glass eels. It is this post-larval life history stage at which river eels enter the coastal catchments of NSW. Samples were collected at an estuarine site 7 km upstream from the ocean and 5 km further upstream at the Audley Weir, which forms a tidal barrier at the upper boundary of the estuary. Extensive seasonal overlap of the two species was observed in samples collected in the estuary. The more temperate species, Anguilla australis, recruited to the estuary from February through September, while the more tropical species, Anguilla reinhardtii, recruited to the estuary all year round. Glass eels of both species appear to delay upstream migration at the freshwater interface and accumulate below the tidal barrier. There was no seasonal overlap of species composition in samples collected at the freshwater interface during the secondary active migration into fresh water. The two-stage migration process may provide a mechanism for temporally isolating the recruitment of multiple Anguilla species into freshwater habitats within a single catchment in NSW.