Sunday, 10 November, 2013 - 07:56

Associate Professor Annick Masselot

There is cause for concern for freshwater fish populations in New Zealand, given even the most conservative climate change estimates.

Increased temperatures predicted under climate change, in conjunction with the influence of invasive species, is a major potential threat to biodiversity and economic and cultural wellbeing of native fish species in New Zealand.

University of Canterbury (UC) freshwater ecology postgraduate student Nixie Boddy says air temperatures in New Zealand are predicted to rise, by up to 7degC in the next century, with a corresponding increase in water temperatures.

In my research, supervised by Professor Angus McIntosh, I measured how the impact of invasive species, such as brown and rainbow trout, on native alpine galaxiid fish might change with increasing water temperatures in four catchments in the Canterbury high country.

Alpine galaxiids are usually about 80 mm long and are a non-migratory relative of the five species that make up whitebait. Invasive trout are a predator of alpine galaxiids and if a trout greater than 150mm long is in a stream, no alpine galaxiids will be present.

Because fish body temperature is determined by the surrounding environment, both native and invasive species may be sensitive to changing water temperatures.

Alpine galaxiids were absent in streams with average summer water temperatures above 14degC and riverbed rock sizes less than 36mm.

Trout greater than 150mm long only persisted in streams with average summer water temperatures less than 10.5 degC, meaning few alpine galaxiids were present in sites with average water temperatures less than 10.5degC.

Differences between catchments were caused by the invader-temperature relationship, whereby when streams with low average summer temperatures warmed up enough that trout could no longer grow to 150mm, it became suitable habitat for alpine galaxiids.

However when warming meant average summer stream temperatures went above 14 degC there was habitat loss as alpine galaxiids were unable to persist.

When different climate change scenarios were modelled in each catchment, results in terms of alpine galaxiid habitat availability were highly variable, with huge increases in some catchments, and others losing all available habitat.’’

The big increases and decreases in available habitat, therefore, depend entirely on local catchment characteristics. This is really important to understand in the context of reserve design and future species management, as changes in habitat availability in response to climate change will be different in every catchment.

These results show that the influence of climate change on native species can be complex if influential invasive species are also affected.

Boddy will deliver a paper to the postgraduate Waterways Centre for Freshwater Management conference, jointly-run by UC and Lincoln University, at UC on Tuesday (November 12).