The brown trout was introduced to New Zealand 150 years ago today, but the freshwater 'sports fish' almost didn't make it here.
Dunedin-based historian Jack Kos has just finished a PhD on the introduction of the brown trout and says
The brown trout came to New Zealand via Tasmania as part of the drive by colonial acclimatisation societies to make countries such as New Zealand feel more like home.
"Species that were considered desirous were brought over to fill perceived ecological gaps in new countries. The colonists erroneously thought New Zealand's rivers were barren and there were very few fish they could relate to.
"This created this perception of a need to replace [the native fish] or to bring fish that were useful and that they would enjoy having here."
Out of the 800 or so brown trout eggs brought from Tasmania, few survived.
"They had a really rough sailing and three of those eggs hatched and then two subsequently escaped, at one point there was just one brown trout in New Zealand but rather remarkably the two fish that escaped managed to wriggle their way into the Avon River in Christchurch and from there two years later they were able to be recaptured."
The acclimatisation crew didn't rely on the tenacity of those early trout settlers, however.
"Huge numbers" were introduced from about 1868 onwards, Kos says.
As to the impact the trout had on New Zealand's waterways, it's a mixed picture.
"I don't think there's any doubt they predate on native species; no indigenous species has been rendered extinct by trout, but there has been a lot of displacement, so more than an eradication there's been a reduction."
Though there have been positive ecological outcomes since the fish took hold, he says.
"You could make a case that trout have had a positive impact on New Zealand waterways, they have provided an avenue for advocacy - Fish and Game has secured numerous water conservation orders. They're also quite a good keystone indicator of the health of a waterway."