95 Lintermans & Raadik—Eradiction of trout from Australian streams Local eradication of trout from streams using rotenone: the Australian experience Mark Lintermans 1,3 and Tarmo Raadik 2,3 1 Environment ACT, P.O. Box 144 Lyneham, ACT 2602, Australia 2 Arthur Rylah Institute for Environmental Research, Department of Natural Resources and Environment, 123 Brown St., Heidelberg 3084, Australia 3 Cooperative Research Centre for Freshwater Ecology mark.lintermans@act.gov.au; Tarmo.Raadik@nre.gov.au ABSTRACT Rotenone has been used for sampling stream fish assemblages in Australia for many years but there have been only two instances where it has been used to eradicate trout populations from streams or sections of streams. In 1992, rainbow trout Oncorhynchus mykiss was removed from c. 2.4 km of Lees Creek, a small montane stream in the Australian Capital Territory. A barrier at the downstream end of the treated section was augmented to prevent trout reinvasion, and the recolonisation of the native species mountain galaxias Galaxias olidus was monitored. The short- term effects of the rotenone treatment on the aquatic macroinvertebrate fauna was also investigated. In 1994 and 1995 a total of 20 km of stream length in seven small streams in the Goulburn River catchment in Victoria were treated with rotenone to remove O. mykiss and brown trout Salmo trutta . This catchment contains some of the only remaining populations of the nationally endangered species barred galaxias Galaxias fuscus which was threatened by predation from invading trout. Barriers to prevent trout reinvasion were first constructed, trout were removed by ichthyocide treatment and the downstream recolonisation by G. fuscus of rehabilitated sites was monitored. The methodology and results for the two projects are presented along with lessons learnt and future directions. 1. INTRODUCTION Trout form the basis of a highly valued recreational fishery in southeastern Australia. However in some areas, the impact of trout on native fish species is severe and control of trout populations is required. Exotic salmonids have had deleterious effects on small native fish of the family Galaxiidae in Australia and New Zealand (Frankenberg 1966, 1974; McDowall 1968, 1990; Cadwallader 1978, 1996; Fletcher 1979, 1986; Jackson & Williams 1980; Jackson 1981; McIntosh et al. 1992, 1994). Both brown trout Salmo trutta L. and rainbow tro ut Oncorhynchus mykiss (Richardson) were introduced to Australian waters more than a century ago, before accurate distribution or abundance data had been collected for native fish species. Consequently, much of the evidence of