Game fish are part of our waterway challenge

New Zealand is a land of biodiversity and where we value our native flora and fauna, be that trees and shrubs, or birds and fish.

We’re struggling with a plethora of issues affecting  our  flora and fauna in waterways. In many cases we are trying to work out how we can undo over a hundred years of land use change, town sewage discharges and impacts from introduced sports, pest fish and wildfowl.

A recent international book on brown trout has a chapter by NIWA scientists documenting the impact brown trout have on our native fish. Brown trout are the most common exotic freshwater fish in New Zealand.  According to the authors the science shows that brown trout can eat their way through native fish, such as whitebait, kōaro, glaxias, at an amazing rate and have significant deleterious effects on native biodiversity.  They’ve been called the stoat of our waterways.

They show in a study that native galaxias in streams without brown trout were plentiful, but in neighbouring waterways with brown trout they had been decimated.  This was irrespective of the land use around the waterways.  

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

Another problem introduced fish is Koi carp. Koi carp where found in the Waikato in 1983 and other introductions have occurred elsewhere for coarse fishing by anglers. The pest is widespread in Auckland and Waikato waterways. They are spreading into Northland and they have been found in isolated places in Whanganui, Hawke's Bay and Wellington.  According to DOC, Koi carp have been illegally released in the Nelson and Marlborough area. 

Andrew McGiven - Provincial President, Federated Farmers Waikato

These noxious pest fish feed by stirring up the bottom of ponds, lakes and rivers, muddying the water and destroying native plant and fish habitat. Koi carp are opportunistic omnivores, which means they eat a wide range of food, including insects, fish eggs, juvenile fish of other species and a wide range of plants. They are like the wild pigs of the waterways.

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 in the process and are unlikely to re-establish, vast amounts of sediment are dislodged in the process. Koi carp cause habitat loss for native plants, fish and invertebrates.  

They are prevalent in lakes in Waikato, especially in North Waikato.  So while farming is having some impacts on those lakes, without control of other factors such as Koi carp – the actions farmers are taking to reduce their impact around these shallow lakes is not going to make much of a difference.

E.coli contamination of waterways can come from farming,  urban discharges and from wild fowl. Recently waterways in Otago have high levels of e-coli attributed to water fowl. Over the summer over 50 beaches in Auckland had do not swim notices issues 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.  All of these problems don’t have easy answers, and will take time and money to fix.

Angling advocates such as Fish and Game are vocal about the need to maintain water quality but I don’t think they acknowledge the negative impact that sport has on our native fish.   

The good news is that 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?

We all want a better environment for future generations and to do this we need impartial science and the ability to work together.  Federated Farmers is doing this with many regional councils and industry groups. I would invite the likes of F & G to do the same.