Andrew McGiven: Waterways challenges for flora and fauna

Andrew McGiven.

Angling advocates are vocal about the need to maintain water quality, but I don't think they acknowledge the negative impact sport has on our native fish.

New Zealanders value biodiversity, but we're struggling with a plethora of issues affecting our waterway flora and fauna.

In many cases we're trying to work out how we can undo more than 100 years of land use change, town sewage discharges and impacts from introduced sports, pest fish and wildfowl.

A recent international book on trout has a chapter by Niwa scientists documenting the impact brown trout have on our native fish. They're our most common exotic freshwater fish, and according to the authors the science shows brown trout can eat their way through native fish, such as whitebait, koaro and glaxias at an amazing rate, and have significant deleterious effects on native biodiversity.

They've been called the stoat of our waterways. Native galaxias were plentiful in streams without brown trout, but in neighbouring waterways with brown trout they had been decimated, irrespective of the land use around the waterways.

Brown trout are linked to the extinction of the New Zealand grayling, the only native fish species known to have gone extinct since European arrival.

Another problem introduced fish is koi carp, found in the Waikato in 1983, with other introductions elsewhere for coarse fishing. The pest is widespread in Auckland and Waikato waterways, is spreading into Northland and has been found in isolated places in Whanganui, Hawke's Bay and Wellington.

These noxious fish feed by stirring up the bottom of ponds, lakes and rivers. They feed like a vacuum cleaner in a very destructive way, sucking up everything and blowing out what they don't want. Aquatic plants are uprooted and are unlikely to re-establish, and vast amounts of sediment are dislodged.

Koi carp cause habitat loss for native plants, fish and invertebrates.

E. coli contamination of waterways can come from farming, urban discharges and from wild fowl. High levels of E. coli in Otago waterways recently have been attributed to water fowl. Over summer more than 50 Auckland beaches had "Do not swim" notices due to contamination from city wastewater.

Improving water quality is something we need to do as an entire community. It won't work if one sector simply blames another while ignoring some of the problems they are also responsible for.

None of these problems have easy answers, and will take time and money to fix. Angling advocates are vocal about the need to maintain water quality, but I don't think they acknowledge the negative impact sport has on our native fish.

The farming sector is working hard on its impacts. There have been some outstanding results in water quality improvement, especially in the Horizons catchments, that are essentially down to farmers being engaged and taking action.

It has not been the result of broad brush, one-size-fits-all rules. How much better would these improvements have been if everyone, including F&G, were part of the solution?