Bowhunters lift pest fish catch over 100 tonne mark

Peter Harrison takes aim at koi carp in the water.

Koi carp were in the sights of bowhunters during an annual gathering aimed at reducing their numbers in Waikato waterways.

Koi carp are now a widespread introduced species which can cause significant damage to the awa and catchments of the Waikato river.

The recent 34th Annual World Koi Carp Classic, centred around the Ōhinewai Hall, north of Huntly, attracted 56 entries.

Participants included members of the New Zealand Bowhunters Society, who hunted koi carp within the catchments and lakes systems of the lower Waikato River’s Koi Catchment Zone.

“Entries were up this year, but very low water levels meant there were fewer koi caught and weighed in, with the total weight just over three tonnes,” said NZ Bowhunters Game Recording Officer Dave Gousmett.

“This was enough to lift the cumulative total of koi carp caught in the history of this event past the 100 tonne mark, which is a lot of koi removed from our waterways.”

Despite this year’s smaller catch, some big fish were weighed in. Hunter Philip Burgess was awarded the Waikato River Authority Trophy for the heaviest koi carp caught with an 8.4 kg specimen, the heaviest fish caught in four years.

In team catches, the ‘River Raiders’ (Graeme Warrender and John Gow) took out the Department of Conservation Cup with 262.8 kg of koi carp caught between them.

Mackenzie Pickering with bow and a captured koi.

The most koi carp were caught in the Waikato River, with 671 koi caught,  averaging 1.94 kg per fish.

Meanwhile, the Department of Conservation collaborated with the competition organisers to conduct a koi diet survey. A number of hunters donated koi for eDNA analysis of their gut contents.

“The genetic analysis of the gut content of koi caught in the Waikato river system will help us to determine what plants, invertebrates and other fish species koi carp are actually eating in the wild and improve our ability to consider how we protect impacted native species,” said Nigel Binks, Freshwater Technical Advisor with the Department of Conservation.

Te Riu o Waikato processed the bulk of the weekend’s catch into products like pet food, fish bait berley and organic soil fertiliser.

Koi carp on display.

Waikato Regional Council Biosecurity Marine and Freshwater Lead, Danielle Kruger, acknowledged the efforts of the bowhunters: “They do a great job every year of removing koi from our waterways during breeding season when the pest fish can be found congregating in their hundreds.”

Koi carp are thought to have been imported into New Zealand accidentally in the 1960s as part of a goldfish consignment.  Wild stocks of koi carp were first found in the Waikato River in 1983, by which time they had likely established a breeding population and begun to spread naturally, during floods and accidentally or intentionally by people.

They churn up sediment to eat invertebrates which impacts water quality, eat native aquatic plant species and compete with indigenous fish for food. Once established in a waterway there are limited control options available to manage them. Holding these types of events is one way to support efforts to manage koi populations.

Waikato Regional Council works in partnership with the Department of Conservation, Waikato River Authority and Te Riu O Waikato as part of the Waikato Koi Management Programme to investigate ways to manage koi carp in the future.