Tauranga fishermen using the Waikato River will soon see less koi carp with the implementation of a new project to control the “pest”.
A project to tackle the pest has been given a major boost with an $85000 funding injection from the Waikato River Authority.
The “Carp-N Neutral” project will involve capturing carp – officially described as an “unwanted organism” and a “noxious fish” – in a special trap at Lake Waikare.
The fish will then be turned into plant food on site using a fish “digester”.
Recent work by the council has shown through their feeding carp incorporate both nitrogen and phosphorous into their flesh.
When digested and dried, the carp mixture is ideal for growing native trees.
Processing the carp will therefore serve to recycle these excess nutrients diffusing into the aquatic environment as a result of intensive farming practices.
Fresh water scientist Dr Bruno David says the WRA’s decision is fantastic news.
“It will help us combat the koi carp plague in a way that protects rivers and aquatic wildlife but also help to grow plants in nurseries which benefit the environment.”
Since the early 1980s, koi carp have “exploded” in the lower reaches of the Waikato River, competing with native species for food and stirring up sediments and nutrients, which can contribute to the growth of toxic algae.
In 2009, a multi-agency trial showed how large numbers of fish could be captured at Lake Waikare, with minimal harm to other species, using a specially designed trap.
The council subsequently agreed to fund the building of its own trap and this is due to be installed this year.
The digester being funded by the WRA and Genesis will be installed alongside the trap allowing a fully functioning “demonstration site” to operate at Lake Waikare.
“The long-term objective of installing the digester is to have an operation that can supply community nurseries with plant food,” says David.
“The idea is to remove some of the excess nutrients diffusing into the river from farming activities and incorporate those nutrients into long term plant growth which will help to protect the river and the environment generally.”
It’s hoped the trap and digester could be a model for other such projects in the future.
“This trap and digester operation will eventually help improve water quality and aquatic diversity, and create new environmental opportunities.
“In time, we’d like to see more of these types of trap and digester sites at other strategic locations within the lower Waikato River basin to really put a dint in the carp population.”