Abstract
The freshwater communities of New Zealand were changed forever when brown trout Salmo trutta was first released in New Zealand by the Otago Acclimatisation Society in 1867, derived from a mixed stock of resident and migratory fish sourced originally from England. Over the next 50 years or so, a combination of widespread introductions and natural spread resulted in brown trout becoming virtually ubiquitous in streams throughout most of the South Island, and much of the North Island. Along with brown trout, Atlantic salmon Salmo salar, rainbow trout Oncorhynchus mykiss, brook char Salvelinus fontinalis, mackinaw or lake trout Salvelinus namaycush, chinook salmon Oncorhynchus tshawytscha, and sockeye salmon Oncorhynchus nerka were also released. Although some species flourished, others such as lake char and Atlantic salmon persist only in isolated populations or are now likely extinct. Of the other species, latitude, climate, and landscape have interacted with the biology of each species to produce relatively stable patterns of co-existence, and most species are at least locally abundant in some systems and locations. Inter- and intraspecific competition and habitat segregation between salmonids, and potentially some native species, likely play a key role in determining patterns of regional and longitudinal distribution in streams, rivers, and lakes, and latitudinal patterns of distribution across New Zealand. Furthermore, complex patterns of distribution of resident and migratory potamodromous and diadromous life histories have also appeared, suggesting environment has a strong influence on life-history type. Many of the patterns of distribution of species and life-history strategies have clear parallels with similar complex patterns of salmonid life history in the Northern Hemisphere, suggesting a major factor in the success of salmonids in the Southern Hemisphere has been their ability to establish their old ways in new lands.