INVASION BIOLOGY AND ECOLOGICAL IMPACTS OF BROWN TROUT SALMO-TRUTTA IN NEW-ZEALAND

Brown trout Salmo trutta were introduced to New Zealand in 1867. Succe ssful establishment was broadly predictable in terms both of the chara cteristics of brown trout and of the receiving community. There is evi dence of impacts of brown trout on the abundance of some native fish a nd invertebrates, and brown trout have been responsible for the local extinction and fragmentation of certain species. An intensive study of the Taieri River has revealed that several native galaxiid fishes are now restricted to headwaters above large waterfalls that prevent the upstream migration of brown trout. Brown trout may profoundly affect t he functioning of stream communities, reducing the abundance of grazin g invertebrates and altering their grazing behaviour so that algal bio mass increases. A trophic cascade was predictable on the basis of the attributes of rite invader and of the stream community. Brown trout se em to have been responsible for the evolution among invertebrates of n ovel antipredator behaviours with far-reaching community consequences. The ecological and evolutionary consequences the introduction of brow n trout New Zealand are probably reversible. Copyright (C) 1996 Elsevi er Science Limited