Call to arms for pest fish battle
The Department of Conservation and Northland Regional Council have jointly declared war on koi carp and rudd, and are calling for public to tell them where the fish are lurking.
“The immediate task in Northland is making sure we know where populations of these serious pests are. We will also be getting expert advice on our options for eradicating and controlling them, and where to focus our efforts,” DoC freshwater technical adviser Amy Macdonald said.
“In Northland we’ve still got the opportunity to protect our waterways from pest fish and stop their spread. We don’t want to end up with koi carp in every pond and river like the Waikato, so now is the time to act.
“Pest fish upset the balance in our freshwater systems, affecting ecological, cultural and recreational values. Koi carp and rudd are both bad news for water quality, so they are also a problem for our agriculture and tourism industries. We’ve all got a reason to work together to stop them spreading and taking over.”
Koi carp, big and brightly coloured, bred prolifically, and could have devastating impacts on waterways. Rudd, smaller but also prolific breeders, ate the growing tips of native aquatic plants, and could turn lakes into barren algae-filled bodies of water that nobody wanted to swim in.
Pest fish expert Helen McCaughan, from Wildland Consultants, had travelled from Christchurch to support the operation, funded from DoC’s Budget 2018 allocation of $76 million over four years to invest in targeted biodiversity initiatives across land, freshwater and marine ecosystems to address the country’s biodiversity crisis.
That funding included $4.5 million over four years to contain key aquatic pest species populations to prevent further spread, i.e. to reduce the likelihood of spread to sites with high biodiversity values, where it would be far more difficult and expensive to control them.
The aim was to contain at least four freshwater pests (koi, gambusia, rudd and hornwort), all serious freshwater pests with the potential to expand to other regions.
Controlling invasive aquatic plants that were likely to seriously risk or impact on freshwater biodiversity values, to reduce their impact on river, lake and wetland ecosystems and the likelihood of dispersal to other indigenous habitats, was also part of the overall project.
The aim was to increase the reduction of invasive aquatic plants by at least 10 sites per year.
DoC and NRC were now seeking reports of “mysterious” fish that could be koi carp or rudd. New reports would be added to the regional pest fish dataset, informing surveillance that was now under way.
To report suspect fish email DoC (whangarei@doc.govt.nz) or phone the NRC on 0800 002-004.
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Koi carp superficially resemble goldfish but grow much bigger, and have two pairs of whiskerlike feelers (barbels) at the corner of their mouth. They are highly variable in colour, often blotchy shades of black, red, gold, orange or pearly white.
They can often be seen over summer, swimming close to the surface in ponds and slowflowing water. When they feed they stir up the bottom, muddying the water and destroying native plant and fish habitat.
Their diet includes insects, fish eggs, juvenile fish of other species and a diverse range of plants and other organic matter, sucking up everything and blowing out what isn’t wanted.
Aquatic plants are dislodged in the process, and are unlikely to re-establish.
Rudd are stocky fish with distinctive red fins and large, shiny scales that range from silver to pale or burnished orange in colour.
They normally grow to about 25cm, and about 500g. The country’s only herbivorous freshwater fish, they are regarded as the ‘possum of the waterways.’
Rudd are found in ponds, lakes and slow-flowing streams.