Editor
Water Magazine
There is a huge debate underway in NZ at present in relation to clean water and the effects from agricultural use of land.
But many people are unaware of the damage done to water quality and our waterways by Koi Carp an introduced fish species which has spread into the wild, become a major pest and is threatening New Zealand’s freshwater species and environments by:
Even if we were to ban farming totally we would still have a problem with water quality from the effects of the Koi Carp.
Koi Carp are designated on the Department of Conservation website as both an:
In relation to water quality Koi Carp must be addressed as they have a huge effect on the rivers. They are one of the most rapidly multiplying invasive pests that have been released into the New Zealand environment.
Koi Carp are now common in our waterways but have been largely ignored with the focus for water quality improvement being almost totally on the effects from agriculture.
Koi carp are widespread in Auckland and Waikato. They are spreading into Northland and they have been found in isolated places in Whanganui, Hawke’s Bay and Wellington. Koi carp have been illegally released in the Nelson/Marlborough area.
It is estimated that there are approximately 500,000 tonnes of Koi Carp in the waterways of the Auckland/Waikato region.
In the Waikato Koi rarely exceed 9 years of age. Females average 5.2 years and males 4.6 years of age. An average fish weighs 3 kg. Females produce 100 000 eggs per kg of body weight. A typical female can produce 300 000 eggs annually (or more if they spawn more than once). Koi carp spawn throughout the summer. As they gather for spawning or feeding in the shallow margins of the river, koi biomass can reach 4000 kg/ha.
Koi carp breed prolifically with a single fish laying between 800,000 to 1 million eggs.
Once established in an area they have a huge and significant impact on rivers and ponds. They destabilize river and pond banks and destroy habitat for native fish and waterfowl. The effect on the water quality is dramatic as they disturb the bottom of streams and ponds as they grub through bottom sediments and uproot plants, significantly increasing water turbidity.
The koi is an opportunistic feeder, eating insects, juvenile fish of other species, a diverse range of plants and organic matter. Once introduced they quickly become the dominant fish in water bodies.
Koi Carp is now rapidly becoming one of the worst invasive pests in New Zealand and as such and taking into account their geographic spread, they are a national problem and require a national solution and appropriate funding from central government to allow control measures to be implemented across the whole country.
To have any chance of success in addressing the desired improvements in water quality then we “MUST” put in place strategies to deal with the invasive pest fish species such as Koi Carp and Catfish and have these included in national environmental standards.
Failure to address the pest fish issues will result in water that will be too sediment laden for swimming and there will be no native flora or fauna left after the Koi Carp have finished feeding.
Andy Loader
Co-Chairman P.L.U.G.
(Primary land Users Group)