The New Zealand Bowhunters Society has removed more than four tonnes of pest fish koi from the lower Waikato River catchment over the weekend.

The 33rd World Koi Classic, which is the brainchild of past president Allan Metcalfe, is a fun competition for New Zealand bowhunters who vie for titles such as heaviest koi, most total kills, most fish per team and even smallest carp – but it also comes with some serious biosecurity risks.

This year, the event was sponsored by the Waikato Koi Management Programme (WKMP), a partnership between Waikato Regional Council, the Department of Conservation (DOC), Waikato River Authority and Te Riu o Waikato, which was set up in 2020 to trial new methods and research approaches for the control of koi carp in Waikato waterways, including installing carp barriers and supporting community-led action.

Andrew Cottle and Sam Walter, pictured with DOC Freshwater Pests and Migratory Fish Species Ranger Anita Pearson, shot a record total of 1092.09 kilograms of koi in the Whangamarino wetland.

Michelle Archer, WKMP workstream lead for Waikato Regional Council, says the competition is an excellent resource when it comes to koi management, but there are a lot of biosecurity risks to consider when moving between waterways.

“There are a number of invasive aquatic species that bowhunters can inadvertently move around, either on their gear or by boats and trailers,” says Michelle.

“Obviously, we’ve got koi – their eggs can be spread if they’re on aquatic weeds – but we also have hornwort, golden dodder and alligator weed. Also, the invasive and unwanted organism gold clam was discovered in the Waikato River this year and remains a persistent concern.

“So, WKMP helped the organisers with their biosecurity planning for the event and making sure that information and equipment was available to help the bowhunters plan their movements and undertake effective cleaning.”

Dawn Metcalfe, from the New Zealand Bowhunters Society, checks compliance of Check Clean Dry regulations of boat Koi Killer.

The discovery of gold clam has heightened the Check-Clean-Dry (CCD) message that WKMP has been sharing at events on the Waikato River this year.

Efforts to prevent the spread of aquatic pests included full checks of all equipment, a wash-down (hot water or bleach for absorbent materials) and the thorough drying of all gear.

Water-blasters, bleach, hoses and sprayers were provided so there could be no excuses by competitors for not following the Check Clean Dry procedures.

DOC, which has sponsored the event for the past 30 years, had staff members present at boat ramps and at the final weigh-in to educate and monitor the competitors to ensure they complied with the Ministry of Primary Industries Check Clean Dry regulations to reduce the risk of moving unwanted organisms between waterways and/or further up the Waikato River.

DOC Technical Advisor, Freshwater, Nigel Binks says koi are commonly seen in the lower Waikato River system and they are regarded as a pest because their foraging behaviours degrade the quality of freshwater habitats and impact the survival of native species.

Some entries for the World Koi Classic.

“Removing koi helps to reduce the impact of this species on native aquatic plants, fish, and invertebrates, and is important for the protection of quality habitats needed by native fish, such as long and short finned eels, black mudfish, inanga, and giant kokopu,” says Nigel.

“DOC supports this event and applauds the efforts of the bow-hunting community in their endeavour to advocate and educate their community about key biosecurity concerns in both the water, and on land.”

Over 40 competitors took part in the World Koi Classic, shooting a total of 4113 kilograms of koi over the two days, with weigh-ins at the Ohinewai Hall.

The winning team, hunters Andrew Cottle and Sam Walter, shot a record total of 1092.09 kilograms of koi in the Whangamarino Wetland – 865 kilograms of koi on Saturday.

The largest koi caught in the competition weighed 5.8 kilograms and the smallest carp was just 200 grams.

Te Riu o Waikato Board Chair Tawera Nikau said all koi caught would be processed by their organisation into pet food, fish bait Berley and organic soil fertiliser.

“They used to dig a hole and bury all the koi carp. We want to thank them for respecting the mauri of the river so that we can dispose of them in an efficient way.”

Mana whenua Ngā Muka also helped with the running of the classic, including assisting the bowhunters with advice to support their permits and ensuring the event worked within the requirements of the rahui on Whangamarino Wetland.

The WKMP team will again be at Lake Kārapiro between now and May, targeting all the major events which get attended by thousands of competitors, supporters and spectators.

For information on Check Clean Dry, visit thisisus.nz/check-clean-dry.