The effects of brown trout on the trophic webs of New Zealand streams

Abstract

The impacts of invasive fish on natural communities have been documented in freshwater ecosystems worldwide. In New Zealand, the most widespread and common invasive fish is brown trout and these fish have caused major changes to both instream processes and the communities that exist in these habitats. This chapter will examine the impact that brown trout have had on trophic webs throughout New Zealand at each level of ecological organisation and at different spatial scales (e.g., microcosm to catchment). The first part of the chapter will focus primarily on New Zealand-based research that addresses: (1) the influence of brown trout in altering invertebrate behavior; (2) the effect of brown trout on native fish communities; (3) what impact brown trout have had on stream food-web structure and how these changes alter other trophic levels (e.g., trophic cascades); and (4) how brown trout can affect stream production and nutrient dynamics. The second part of the chapter will examine processes that influence the extent of these brown trout effects. This part of the chapter will examine how brown trout effects operate, and potentially differ, at varying spatial scales and will also outline the role that physical factors play in altering brown trout impacts on trophic webs in New Zealand streams.