Koi carp are high on the list of animal pests at the Department of Conservation, and have become an increasing concern throughout the lower Waikato River basin.
And there is cause for alarm for farmers in wetland areas, or who have low lying lakes, or waterways on their farms.
This ornamental native of Asia and Europe was thought to be introduced to New Zealand in the 1960s as part of a goldfish consignment. Their release into the wild was caused by largescale flooding, and illegal introductions for coarse fishing.
With no natural predator in the ecosystem, they can live for 30 to 40 years, preferring still waters. A female is capable of laying 300,000 eggs a year, and breeding is prolific.
When koi carp feed, they stir up the bottom of the waterways, sucking up everything and blowing out what isn’t wanted. The dislodged aquatic plants and undermining of stream banks causes habitat loss for plants, native fish, invertebrates and waterfowl.
This year Conservation Minister Eugenie Sage asked the Department of Conservation to investigate ways of eradicating the fish. A new Waikato pest fish coordinator is in place and is implementing a number of key projects including a strategy around long-term eradication of koi carp during the next 10 to 15 years. These projects are provided for out of a new freshwater biosecurity fund.
Under operations director David Speirs DOC is looking at Australian research that plans to release the koi carp herpes virus into their waterways. Determining whether this is a viable option for New Zealand will be a long process but work has commenced on initial legislative requirements.
DOC is also working with local iwi to consider baiting, netting and trapping the carp, and processing them into nutrient rich fertiliser during the eradication operation.
On a smaller scale in non-flowing habitats, farmers are involved in projects such as containment, one-way traps, rotenone (pesticide), netting, and electric fishing.
In the containment area between Auckland and Hamilton, recreational fishing is allowed, provided all koi carp are killed.
Primary Stakeholders Catchment Trust (Lake Waikare) chairman Jim Cotman has been involved with farmers in the Whangamarino wetland, and their concerns with the carp.
“Every time there is a flood, they move further up the drains, become trapped and die in their hundreds.
“Our farmers see first-hand the havoc caused to their farm waterways, and the subsequent nutrient and sediment loss to the rivers, lakes and wetlands they feed.
“This sets the scene for increased erosion and sediment loss downstream.”
North Waikato farmers have sent submissions to Waikato Regional Council for the Waikato Healthy Rivers Plan Change 1 to include provision for the control of koi carp, as they see the pest fish as part of the cumulative effects on the Waikato River.
Last month Parliament passed a Conservation (Indigenous Freshwater Fish) Amendment Bill, which aims to update legislation to look after fish spawning areas, ensure culverts and drains don’t block fish passage in rivers and streams, and manage fishing on conservation lands.