New Zealand Journal of Ecology (2010) 34(1): 195- 206

The impact of trout on galaxiid fishes in New Zealand

Review Article
Angus R. McIntosh 1,*
Peter A. McHugh 1,5
Nicholas R. Dunn 2
Jane M. Goodman 3
Simon W. Howard 1
Phillip G. Jellyman 1
Leanne K. O’Brien 4
Per Nyström 6
Darragh J. Woodford 1
  1. School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
  2. Department of Zoology, University of Otago, 340 Great King Street, PO Box 56, Dunedin, New Zealand
  3. Department of Conservation, Gisborne, New Zealand
  4. Ichthyo-niche, 26 Main South Road, Dunedin 9018, New Zealand
  5. Utah State University, 5290 Old Main Hill, Logan, Utah, 94322, USA
  6. Department of Ecology, Ecology Building, Lund University, S-223 62 Lund, Sweden
*  Corresponding author

Compared with the effect of invaders on the native terrestrial fauna of New Zealand, interactions between native fishes and introduced trout (sports fish in the genera Salmo, Oncorhynchus and Salvelinus) are less well known and there have been fewer efforts to remedy their effects. Trout have caused widespread reductions in the distribution and abundance of native galaxiid fishes, a family dominated by threatened species. The effects have been most severe on non-diadromous species (those lacking a marine migratory stage), which are commonly eliminated from streams by trout. Galaxiid populations in lakes, and those with migratory ‘whitebait’ stages, have also been affected, but the extent of the impacts are less understood. The mechanisms controlling negative interactions between trout and native fish, and how the environment modifies those interactions, will be important for future management. Experiments and field comparisons indicate size-specific predation by trout is the main driver of negative interactions. Large trout (>150 mm long) do the greatest damage and small galaxiids (those with adult sizes