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An animal becomes a pest if it begins to cause considerable economic or environmental damage.

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Image credit: Sjaan Bowie | DOC

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Cyprinus rubrofuscus

Origin: Eastern Asia
Discovered in NZ: 1983, Waikato River
Reason: likely to have been a released pet

Habitat: Koi carp prefer slow or non-moving waterways like ponds and wetlands.

Max Size: 120cm, 40.1kg

Koi Carp cause damage by eating plants and insects as well as stirring up mud.

Can lay up to 1 million eggs at a time and spawns up to 3 times per year in New Zealand. The eggs are sticky and easily transferred between waterways.

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Image credit: Sjaan Bowie | DOC

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Scardinius erythrophthalmus

Origin: Europe
Introduced: 1967, illegally
Reason: fishing

Habitat: lakes, ponds, large weedy pools in rivers and streams.

Max Size: 61.7cm, 3.62kg

Rudd breed rapidly and eat plants and plankton, damaging native aquatic plants and starving native fish and insect species.

*They are considered a pest fish in New Zealand except in the Auckland and Waikato regions where they are considered a sports fish.

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We have listed species that are considered pests in Aotearoa - but it's not always that simple: A fish may be considered a pest in one region, but a sports-fish (something people like to catch) in another region or situation.
This is an example of people having different values - sometimes we value a species despite its impact.
Take a look at the case of trout in Taupō to investigate this idea further.

In this Padlet fish considered sport-fish in some regions or situations are marked with an asterisk.

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Image credit: Angus McIntosh

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From NIWA Freshwater Invasive Species of New Zealand 2020

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A short, silly video about Check, Clean, Dry, a key way that we prevent the spread of pest species.

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Pest fish illustrations by Sonia Frimmel.

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Image credit: Gilles San Martin

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Gambusia affinis

Origin: Gulf of Mexico
Introduced: 1930s
Reason: mosquito control

Habitat: Shallow and sheltered margins of lakes, wetlands, rivers.

Max Size: 6cm (females), 4cm (males), 3g

Although small, the mosquitofish is extremely aggressive and have been known to kill fish many times larger than them. They will eat anything that moves and outcompete other fish in most habitats they invade. They will also quickly overpopulate a habitat and pollute the water with their waste. They give birth to live young and a female can give birth to 20 babies once every 19 days.

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Rudd (Scardinius erythrophthalmus)

Scardinius erythrophthalmus is a benthopelagic freshwater fish native to Europe, Russia and central Asia. It is a very invasive species and was illegally introduced into New Zealand in the 1967s via a private consignment of juvenile rudd which was then reared to adulthood and encouraged to breed. Since then they have been illegally spread deliberately and strategically into a number of lakes, ponds and rivers throughout the North Island as well as Canterbury and Nelson. They are widespread in Auckland and Waikato with isolated populations in Northland, Whanganui, Wellington, Nelson and Christchurch.They are a voracious fish that compete with New Zealand's native fish and cause irreversibly damage indigenous ecosystems. Adult rudds are predominantly herbivorous and feed preferentially on native macrophytes (aquatic plants), while juvenile rudd feeds voraciously on zooplankton (tiny aquatic animals). These feeding habits endanger native plant species, destroy indigenous habitat, remove food sources for native fish and invertebrate species, and potentially impact negatively on water quality by stirring up bottom sediments and muddying the water.They are a stocky, deep-bodied fish with distinctive red fins and large, shiny scales that range from silver (juveniles) to pale orange (adults) in colour. Rudd normally grows to about 25 cm, and about 500 g. They are highly productive, with females able to produce up to 50,000 eggs per kilogram of body weight.Legally they are classed as a noxious species (except in Auckland/Waikato Fish and Game region where it is a sports fish). Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cypriniformes
Family: Cyprinidae
Genus: Scardinius
Species: S. erythrophthalmus
Binomial name: Scardinius erythrophthalmus
Common names: Rudd, Common rudd, often referred to as 'possums of the waterways'

Thanks to Wikipedia for text and information http://creativecommons.org/licenses/by-sa/3.0/

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t.e.r:r.a.i.n - taranaki educational resource: research

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T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

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Scardinius erythrophthalmus is a benthopelagic freshwater fish native to Europe, Russia and central Asia. It is a very invasive species and was illegally introduced into New Zealand in the 1967s via a private consignment of juvenile rudd which was then reared to adulthood and encouraged to breed.

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Why bring these species to Aotearoa?

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An aging communist armed with oxygenated fish tanks in his car roamed New Zealand's countryside for decades in a bizarre crime spree that forever changed our environment. It led him to be called one of the country's worst environmental criminals; but to some, his legacy is much more complicated.
Stewart Smith is an old man, propped up on a zimmer frame in the morning darkness.

He is delicate on his feet, re-learning how to walk after surgery on one hip and both legs, watching in silence as they raid his workshop, the product of his life's work.

It was 5am, and they numbered around 30. They broke the chains on the fence surrounding the building. They quietly moved past a giant concrete tank sucking water through a bore and feeding it through the building.

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Many decades earlier, the old man earned the nickname Shotgun Smith for how aggressively he defended his West Auckland garage from thieves. Now he is 92-years-old, living alone in his West Auckland lair, pondering what to say when they discover what he has in his tanks.

It happened by pure coincidence. A few weeks earlier, a boy was alone and wandering the streets in Massey. He came across a Caltex petrol station; next to it, he saw a crumbling old garage, paint peeling from the exterior.

Something catches his eye. Near the petrol station forecourt, a creature is wriggling in the gutter. It looks like a kōura, but larger; most strikingly, it has a steely dark shell.

The boy goes home and tells his dad. When they return, dad wraps the creature in a sweatshirt, and they bring it home to their fish tank.

He rings the Department of Conservation, which sends someone out to investigate. The official immediately recognises what he's looking at; a West Australian smooth Marron, a species not found in New Zealand.

Word gets around, and several agencies discuss next steps. They know that, based on where the marron was found, there were likely to be more.

A biosecurity report prepared two months later said marron "have the ability to become widespread throughout New Zealand, invade many habitats, affect ecosystems and all levels of the food chain".

They needed to move quickly, so the raid happens 16 days later, early on a Monday.

For most of the day, Smith watches. At first, he says nothing. Then they figure out what he's up to, and he knows the jig is up.

POMMIE BASTARD

About a decade ago, a writer named Bryan Winters was told about a communist who loved to fish.

It caught his interest

"He'd left quite a lot of money, and part of his last will and testament was he wanted a book published telling his story," Winters says.

Stewart Smith had even suggested a title: That Pommie Bastard.

The life of J. Stewart Smith was long, colourful, and driven by an uncommonly strong sense of purpose.

By the time he died in 2008, aged 95, Smith had left a permanent legacy in his adopted country's bloodstream - its network of ponds, rivers and lakes.

This account of Smith's life and legacy is based on official documents and hundreds of pages of Smith's personal notes obtained by Stuff, as well as interviews with people who knew him. several of whom requested anonymity.

They reveal an enigmatic figure largely forgotten in New Zealand's recent history, but one who has had an outsized, and permanent, impact on the country's environment.

"Imagine if one guy was responsible for the introduction of rats, possums, rabbits, stoats and pigs to New Zealand," one former official familiar with Smith's activities says.

"Stewart Smith was pretty much that guy, but he just did it to freshwater ecosystems around the country."

Over the course of four decades, Smith released many thousands of fish into rivers, lakes and ponds. The vast majority of his liberations were illegal.

He was prosecuted at least twice, but Smith continued his releases well into old age. Age made him bolder, more audacious, culminating in the 2005 raid on his home, which likely stopped what Smith planned to be his last, and most significant, liberation.

"He's had more impact on freshwater than any other single human being," another former official who pursued Smith says.

"He was really one of New Zealand's arch environmental criminals."

For much of his adult life, Smith would breed exotic fish in a network of tanks behind his Massey workshop and release them into waterways.

He outfitted his car - initially a Ford Zephyr, and then a Lada Niva - with oxygenated fish tanks that could keep fish alive for days.

He would liberate the fish wherever he could, with or without the permission of land-owners. He would recruit accomplices - sometimes adults, sometimes children - in raids on farms, dams, and public waterways.

Smith diligently chronicled his activities.

According to his own records, Smith was personally responsible for liberating more than 15,000 fish between 1964 and 1987, in hundreds of distinct locations. The vast majority were in the upper North Island, between Rotorua and Kerikeri, but extend as far south as Christchurch.

He liberated fish in small farm ponds and major rivers; pristine dune lakes and city water supplies. His address book bulged with people who had asked him for fish, which he always supplied, sometimes as far away as Wellington.

He would smuggle fish eggs into the country by hiding them in his pocket while going through customs, and once, in the vegetable pantry of a passenger ship. He established a new species in New Zealand from a handful of fish eggs an associate sent to him in the post.

"He was clearly a hugely resourceful and tenacious man, with an incredible amount of passion and drive," one of the former officials said. "It's such a shame when you think how that energy could have used towards something positive."

The fish he liberated, generally speaking, flourished.

Much like New Zealand's native land birds, its freshwater fish had evolved in an environment with few natural predators. New species can shake up an ecosystem that evolved in a delicate equilibrium - and in New Zealand, the result has been chaotic.

A COARSE HOBBY

To understand why Smith did what he did, it pays to understand the long-simmering battle over who gets to fish what.

New Zealand has several dozen native freshwater fish, most of which are nocturnal, discrete, and tucked away in streams far from civilisation. Few of them grow larger than 10cm; they don't make for great angling.

Recognising this, early European settlers decided to bring their favourite sports fish with them: Trout. Trout flourished in New Zealand's cooler waters, with limited competition from native species. The trout fishery is now so prosperous it attracts anglers from around the world.

Some immigrants, including Smith, did not grow up trout fishing, which in England was a sport reserved for the elite. They fished for the so-called "coarse fish" - among them rudd, perch, tench and carp, named for their rough skin.

This class divide bled into New Zealand. While trout soon followed the immigrants, attempts to bring in coarse fish were rebuffed, largely because they would compete with trout.

And so Smith, who paid dues to New Zealand's communist party for much of his life and had a pathological dislike for social hierarchy, sought to equalise the playing field.

Smith's liberations began in the early 1960s, work he did concurrently with running his commercial garage on Triangle Road in Massey.

He started with one of the most damaging coarse fish: Perch.

Perch were already in New Zealand, having been brought from Tasmania in the 1860s, and were predominantly found in Canterbury and Otago. They were not widespread, for good reason - perch are carnivorous and have a ravenous appetite. Not only do they eat other fish, they also eat each other.

Smith likely started with perch because he had easy access to them. In 1905, a population had been legally introduced to Lake Rotoroa in Hamilton city, and had survived. Smith, with the help of two local boys, took perch from the lake and spread them around Auckland.

His notes show he introduced hundreds of perch to Auckland lakes in the 1960s, primarily in Western Springs and Lake Pupuke. In 1965, Smith broadened his liberations to include tench which he obtained from a contact in Waimate. He started with four, which was enough to establish a breeding stock at what he called his "office pond", behind his garage.

As his operation ramped up, Smith started breeding goldfish (a type of carp, not the type commonly kept as a pet), koi carp, gambusia, and golden orfe.

But it was another fish that became Smith's signature - Rudd. Rudd are a stocky freshwater fish with coarse skin and ruby-red fins; They are prolific breeders, releasing thousands of eggs at a time.

They primarily eat aquatic plants, preferring natives over exotics, meaning they share a diet with native freshwater species. For that reason, rudd are sometimes called 'the possums of waterways'. There had been no rudd in the Southern Hemisphere until Smith liberated them into a pond at Wainui school, north of Auckland, in 1969.

Over the course of 20 years, Smith released more than 10,000 rudd, 2300 tench, 1000 perch, and hundreds of koi, goldfish, and orfe.

He had his favourite spots; Among them was Waikato's Waihou River, where he once released 2000 rudd in one go at the Te Aroha boat ramp.

Although he typically avoided major waterways, likely because it increased the odds he would be seen, he still managed to populate them with fish. One strategy was to liberate fish into a nearby drain or stream, which, upon the next flood, would sweep fish into the river.

Smith was so prolific it became difficult to keep track of where the fish were ending up.

"He was always moving around," says one former Smith associate.

"He would say I've done this, I've done that, places all around the country... He even told me he put a whole lot of stuff in the South Island, that he'd moved koi carp to a particular lake on the West Coast. You don't know whether it's true or if he was making it up."

Authorities noticed the sudden appearance of rudd, a species never before seen in New Zealand. They knew who was responsible - Smith regularly bragged about his liberations. He was even profiled in the Auckland Star, under the headline 'Rudd doing well - now for gudgeon', complete with a photo of Smith.

Not long afterwards, in 1974, Smith was prosecuted for the first time. His fish were destroyed, his tanks were poisoned, and his car was confiscated, a setback which stopped his liberations for four years.

"Fascism is a long way from dead," he bitterly wrote in his diary.

That period, however, came with vindication. In 1975, rudd was declared acclimatised in Auckland and Waikato, essentially recognising that it was here to stay. To this day, Auckland/Waikato is the only region where rudd is established to the extent it is not considered "noxious", a feat entirely due to Smith.

Smith's fish continued to spread, even though his liberations had paused.

When he started up again, he realised his fish had been too prosperous. He decided to start releasing perch again, under the logic they would predate on rudd and tench.

It was at this point he started falling afoul of his few allies. Not only had he returned to spreading perch, he was also releasing koi carp, a bottom feeder notorious for damaging waterways. He was talking about importing gudgeon, and even flirted with bringing in pike, a ferocious carnivore likely to dominate any freshwater body it could find.

Smith's notes end in 1988, when he was prosecuted once again, this time by the Auckland Acclimatisation Society. His fish were destroyed, and his equipment and notes were seized; He was fined $4950, and his beloved Lada Niva was confiscated.

Although he had stopped taking notes, there were numerous sightings of Smith around rivers and lakes in the early 2000s. He was hard to miss: He was an octogenarian, roaring about the countryside in his new, $40,000 off road vehicle.

A 2003 report produced internally for the Department of Conservation and seen by Stuff notes several of these sightings. The report was ostensibly about threats to Auckland's freshwater ecosystems; a major one of those threats, it concluded, was Stewart Smith, who was referenced by name dozens of times.

There's a pristine lake near the Kaipara Harbour, at the northern edges of the Auckland Region, called Lake Rototoa.

It is one of a group of dune lakes, dotting the western coastline. Rototoa is the best of them; it is the largest, deepest lake in Auckland, and for a while, the only one dominated by native fish. Among its population were dwarf inanaga and dune lake galaxias, both of which are highly rare and on the brink of extinction.

Then Smith started his liberations.

In 1970, his notes show, he liberated more than 100 rudd into Rototoa. They prospered. So much so that, 30 years later, Smith returned with perch, in an effort to control the rudd he had unleashed.

It proved to be a near fatal blow for the lake.

Rudd, which feed on native macrophytes, reduced the lake's water quality. Then the perch started dominating the native species. Between 2003 and 2011, monitoring showed dwarf inanga numbers had dropped by more than 99 per cent, and the species is now functionally extinct in the lake. Kōura numbers had dropped by 90 per cent, and common bullies by 80 per cent.

The lake had also been a popular rainbow trout fishery, but almost immediately after perch were introduced, the fishery collapsed.

It's a common story when exotic fish are introduced; just like rats and possums on land, they tend to dominate whatever ecosystem they end up in.

"Competition between native species is very balanced in an ecosystem," says Dr Cindy Baker, a freshwater fish scientist at NIWA.

"They tend to have different niches and it all works together well. Once you put these introduced fish in, you have more overlap in niches for certain species, and that's where you have more competition for food resources."

Introduced fish have a significant effect on New Zealand's freshwater biodiversity, Baker says, particularly in lakes, from which they are hard to remove.

He was an old man, now, but Stewart Smith had a plan.

He could no longer roam the countryside, but he could still breed fish. Which is why he dreaded what the authorities would do when they looked inside his tanks: He knew they would find 600 gudgeon, a species never seen before in New Zealand, which he was planning to release in Lake Taupō as his final act.

Smith had talked about this plan for a long time. He first mentioned it off-handedly in a 1972 news article in the Auckland Star, then again in a 1988 news article. But it wasn't clear how serious he was. In the twilight of his life, he had wanted to breed enough gudgeon, approximately 10,000, to fill the lake.

"It would have been horrific," one of the former officials, who had knowledge of Smith's plans, said.

It's not entirely clear how Smith smuggled gudgeon into the country. An investigation concluded Smith had likely received them from an associate who had since died. Due to a lack of evidence he had imported them himself, Smith was not prosecuted.

An internal biosecurity report said gudgeon "were considered likely to become widespread throughout New Zealand in all lowland freshwater systems, and were ranked as having potentially high impacts on both native and introduced fish species that inhabit these environments".

The day after the raid, gudgeon was declared a pest species, allowing them to be destroyed. Smith's tanks were cleansed, leaving him with nothing.

Gudgeon were also found in a pond near Helensville, and exterminated there, too. Smith had told one associate he released gudgeon in potentially dozens of other waterways, including the Hikutaia Cut, which would have been devastating; it is connected to the Waihou River, which, as the biosecurity report said, "would mean the feasibility of eradication from these waterways is extremely low".

A sweep of those waterways found no sign of gudgeon, although no extensive search was undertaken in the Hikutaia Cut or the Waihou. To this day, it is unclear if gudgeon were ever released.

Following Smith's death in 2008, authorities returned to his lair to destroy whatever he had left in his tanks. They were let in by Smith's nephew, his closest relative, who was not in any sense close to his uncle.

They expected to find more gudgeon, but didn't; just a few schools of rudd. Nevertheless, the tanks were drenched with a lime solution to destroy any trace of life, and a sucker truck dealt with the contaminated water, ending the complicated legacy of Stewart Smith.

"Like us all, I think he was an inconsistent personality," Bryan Winters says.

"He enjoyed fishing, and genuinely felt that spreading these fish around was going to benefit people. I don't think he approached it like some evil ogre, thinking 'I'm going to do harm to New Zealand by doing this'."

In his writing, Smith often talked about the joy of fishing, particularly for children. He believed New Zealand was deficient in this sense - apart from eels, which he believed were too scary and snakelike for kids, there was no way for a child to grow up fishing in the way he did.

Curiously, Smith himself was not a regular angler, even though an entire coarse fishing subculture had emerged in his wake.

"He came to some of our meetings - he was very well-read and he didn't suffer fools gladly," said John Jossevel, a founding member of the West Auckland coarse fishing club, which began in the early 1980s.

"He didn't do a lot of fishing himself, for enjoyment or pleasure."

Smith is still advancing his cause beyond the grave. Every couple of years, several coarse fishing clubs receive a $5000 donation from the 'S Smith Trust', financial documents show. Last year, the West Auckland club received $10,000. It pays for trophies and catering and stationery and other things that keep the club going.

Stewart Smith is a boy, roaming the streets of East London with his fishing rod.

He often fishes alone, in the Lea canal, while the other boys play rugby after school. He sometimes finds little ponds, where he fishes for perch, pike, and best of all, gudgeon; When he hooks a gudgeon, he sells it to other fishermen to use as bait.

He loved his parents, even when money issues ruined things. His father was a gambler, he wrote, and once loudly abused his mother while Smith listened in the next room.

But there was always fishing: "My childhood in England was happy, largely due to those hours spent fishing," he later wrote.

Smith was only 15 when his father told the boy that he and his brother would be going to New Zealand, alone. His coarse fishing days, and his childhood, was over. But it didn't have to be for the next generation.

"He said to me once, the greatest pleasure a boy can have is fishing," one person who knew Smith said.

"He was always yearning for that boyhood pleasure he had fishing in the canals as a boy. He wanted to replicate that here."

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The Liberator: How one man's 15,000 pest fish changed New Zealand's waterways

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An aging communist armed with oxygenated fish tanks in his car roamed New Zealand's countryside for decades in a bizarre crime spree that forever changed our environment. It led him to be called one of the country's worst environmental criminals; but to some, his legacy is much more complicated.

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Image credit: Glen Maclean

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Image credit: A Siciliano | DOC

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Ameiurus nebulosus

Origin: North America
Introduced: 1877 (but relatively recent spread)
Reason: food source

Habitat: Catfish prefer slow-flowing, shallow waters with silty or muddy bottoms.

Max Size: 55cm, 2.7kg

Catfish cause damage by stirring up mud and eating kōura, insects, small fish and plants. They breed rapidly laying up to 10,000 eggs which are protected by both parent fish.

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Meet some 'aliens'! This is an Australian example.

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Carassius auratus

Origin: Asia
Introduced: 1860s
Reason: pets, released as fishing targets

Habitat: Goldfish prefer shallow areas of ponds, wetlands, or slow moving streams with lots of water plants or weeds.

Max Size: 48cm, 2.4kg

Goldfish lay up to 50,000 eggs at a time, and can spawn (lay eggs) several times per year. The eggs are sticky and can easily be transferred between water bodies on boats, fishing gear or clothes.

In several areas they are considered a food fish by Māori.

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From NIWA Freshwater Invasive Species of New Zealand 2020

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From NIWA Freshwater Invasive Species of New Zealand 2020

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From NIWA Freshwater Invasive Species of New Zealand 2020

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All about Koi Carp - thorough and easy read including 'click' definitions.

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Koi carp ( Cyprinus carpio Linnaeus, 1758) are a brightly coloured fish native to Asia and Europe. They are an ornamental variant of common carp ( Cyprinus carpio carpio) and were developed by selective breeding from the Asian subspecies Cyprinus carpio haematopterus. They are one of the most popular ornamental pond fish in the world - some colour variants sell for thousands of dollars (especially in Japan). In the wild, koi carp keep their colour but not the forms that command high prices overseas. Feral koi carp have become a pest fish found on every continent in the world except in Antarctica.

An introduced species

The species is thought to have been introduced to New Zealand waters in the 1960s. They may have been released accidently from ponds during flooding. Some may have been released for fishing purposes. Feral breeding stocks were first noticed in the Waikato River in 1983. They are now very common throughout the lower Waikato River regions - spreading into streams, lakes and wetlands. They make up the largest fish biomass (up to 80%) in the lower Waikato River regions where slow, turbid water and shallow lakes and wetlands provide ideal habitat.

What do they look like?

Wild common carp tend to be a green colour, but our stocks are derived from the ornamental Japanese koi so they often exhibit patterns of black, red, orange, gold and white splotches. Koi carp in New Zealand can grow up to 12 kg in weight and 75 cm long. Koi have two pairs of whisker-like feelers called barbels at the corner of their mouths. About 1% of the Waikato koi are goldfish hybrids - identified by their large size relative to goldfish. These koi do not have barbels or they have a single pair of barbels.

Breeding

Waikato koi rarely exceed 9 years of age. Females average 5.2 years and males 4.6 years of age. An average fish weighs 3 kg. Females produce 100 000 eggs per kg of body weight. A typical female can produce 300 000 eggs annually (or more if they spawn more than once). Koi carp spawn throughout the summer. As they gather for spawning or feeding in the shallow margins of the river, koi biomass can reach 4000 kg/ha.

What damage do they do?

Koi carp feed like vacuum cleaners - moving along the bottoms of streams, lakes and rivers. Koi carp are opportunistic feeders eating a wide variety of benthic organisms - plants and animals. They suck up and expel material from the bottom, filtering out edible material as they go. They grind their food to a pulp with powerful teeth located in their throats, making a noise that can be heard underwater through a hydrophone.

This activity destroys native plant, fish, invertebrate and water bird habitat. It stirs up the substrate and can greatly increase the turbidity of the water. Waterways become muddy and unattractive. Aquatic plants are dislodged and are unlikely to re-establish. Oxygen is depleted.

Like a number of exotic freshwater fish, koi carp are a threat to our native freshwater fish.

Where are they found?

Koi carp prefer still waters, spreading from rivers into lakes, streams or backwaters in rivers. They are highly tolerant of poor water quality - surviving well in degraded water and contributing to the decline.

Although koi tend to stay within a restricted home range, they are powerful swimmers, and individuals may make extensive journeys to spawning habitats or for feeding. One tracked fish made a return trip of 104 km in 197 days while another made a return trip of 208 km in 196 days. Other fish have been recorded travelling upstream from Lake Whangape into the Waipā River, a distance of about 120 km. The Karāpiro dam prevents koi movement further upstream in the Waikato.

Koi carp are widespread in the Waikato and Auckland and are spreading further north. They have also been found in Wanganui, Hawke's Bay and Wellington but have not yet been found in the South Island.

Containing and controlling koi carp

Initiatives have been set up in the Waikato to help contain and control koi carp. Koi carp recreational fishing (especially bow fishing) is encouraged in certain lakes in the Waikato. Competitions are set up annually near Huntly. In the spring of 2010, 8.6 tonnes of koi were caught from a lake in one weekend. Koi carp caught are made into berley for fishing.

The Waikato Regional Council is working to eradicate koi carp. Gates, traps and digesting machines are currently being set up to catch and destroy koi carp in lakes near Huntly. These fish are made into fertiliser for riparian planting along the river and around lakes.

Nature of science

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Koi carp (Cyprinus carpio Linnaeus, 1758) are a brightly coloured fish native to Asia and Europe. They are an ornamental variant of common carp (Cyprinus carpio carpio) and were developed by selective breeding from the Asian subspecies Cyprinus carpio haematopterus.

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DOC page:

Legal status (and consequences for possession of live fish)

Control options

Monitoring

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Koi carp are an ornamental strain of the common carp ( Cyprinus carpio) native to Asia and Europe. This species is 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.

Further illegal introductions have occurred elsewhere, for coarse fishing (a traditional British pastime involving the catch and release of certain species including koi carp, rudd, perch and tench) and for ornamental purposes. Isolated populations have been progressively discovered throughout the North Island .

What damage do they do?

When koi carp feed they stir up the bottom of ponds, lakes and rivers, muddying the water and destroying native plant and fish habitat. Koi carp are opportunistic omnivores, eating a wide range of food, including insects, fish eggs, juvenile fish of other species and a diverse range of plants and other organic matter.

They feed like a vacuum cleaner, sucking up everything and blowing out what isn't wanted. Aquatic plants are dislodged in the process and are unlikely to re-establish. Koi carp cause habitat loss for plants, native fish, invertebrates and waterfowl. They can also worsen river erosion by undermining banks as they feed.

Legal designation

It is an offence to sell, breed or distribute any Unwanted Organism under Sections 52 and 53 of the Biosecurity Act 1993. Penalties include a fine of up to $100,000 and/or imprisonment up to 5 years (Section 157 (1)).

People who possess, control, rear, raise, hatch or consign Noxious Fish without authority are liable for a fine of $5,000 under the Freshwater Fisheries Regulations 1983.

Under Section 26ZM of the Conservation Act 1987, any person who transfers or releases live aquatic life into any freshwater without prior approval commits an offence and is liable for a fine of up to $5,000.

What's being done to control koi carp

Containment area - Auckland and Hamilton

To help stop their spread, a containment area between Auckland and Hamilton was established in 1990.
Map of the containment area (PDF, 104K)
The commercial harvest of koi carp can take place from waters within the koi carp containment area but you will need approval. See Harvesting koi carp.

Recreational fishing is permitted, but all koi must be killed when caught.

Moving live koi carp is an offence under both the Conservation Act 1985 and the Biosecurity Act 1993, and selling, breeding and distributing koi is also an offence under the Biosecurity Act 1993 and the Freshwater Fisheries Regulations 1983.

Koi are widespread in Northland, Auckland and the Waikato River catchment downstream of Lake Arapuni. They are now found in the Waihou and Piako Rivers. They are also located in isolated places throughout the North Island except East Cape/Gisborne.

There are no known populations of koi carp in the South Island.

Removal of koi from outside the containment area

Koi carp outside of the containment area are considered a serious pest and control options will be investigated, particularly in cases of small and isolated populations of the fish. If you catch or spot a koi carp outside the known geographical extent of the species you should report this or any other sighting to the DOC hotline, 0800 DOC HOT (0800 362 468).

Koi carp have been eradicated from small sites throughout the North Island. Illegal releases of koi carp in the Nelson/Marlborough area in 2000 were eradicated.

Preventing the spread

Check, Clean, Dry methods for all water users

DOC is a member of the Freshwater Biosecurity Partnership Programme, led by Biosecurity New Zealand (part of the Ministry for Primary Industries). This collaborative programme was established in 2007 to target didymo but was expanded in 2016 to include all freshwater pests.

The programme supports a multi-organisation partnership to help prevent the spread of freshwater pests (not just fish) through coordinating work primarily focused on advocacy and pathway management. Advocacy aims to change behaviour around waterways to prevent the unintentional spread of freshwater pests.

It does not have a specific programme focusing on koi carp, however the MPI websites provide cleaning guidelines for water users that are effective across a range of freshwater pests.
Check, Clean Dry measures on the MPI website
Active and passive surveillance

Early detection of new koi sites increases the chances of successfully eradicating them. Planned or active surveillance programmes for pest fish, including koi carp, are conducted by DOC either alone or alongside some regional councils.

A variety of tools and methods are used in surveillance, including environmental DNA (eDNA), where water samples are analysed for genetic material of plant and animal species present in a waterway.

Passive surveillance relies on members of the public reporting any sightings of koi carp. Reports are responded to by DOC and/or regional councils. If you find koi outside of the containment area report it to 0800 DOC HOT (0800 362 468).

Regional pest management plans

The Biosecurity Act 1993 enables the establishment of regional pest management plans and pathway management plans by regional councils and these can also help reduce the spread of pests like koi. DOC has a role in working with individual regional councils in developing these plans and establishing appropriate regional controls.

Control options

The ability to control koi is limited by the small range of tools available and whether those tools to make real impacts on the koi carp population. Although the eradication of koi is highly desirable, it is a challenging goal.

It has taken millions of dollars and 25 years of consistent effort for Tasmania to eradicate carp from an enclosed lake, screening the lake outlet to prevent any fish from entering or leaving the lake, and using multiple methods of physical removal. In New Zealand, koi carp have only been eradicated from small ponds that are hydrologically separate from other water bodies.

Existing tools to control koi include manual removal using nets, traps, electric fishing or recreational fishing, and draining the water body, the use of toxins and selective barriers. These are generally not effective on their own and need to be used in combinations suiting each situation. Most are only effective in enclosed/isolated and/or non-flowing water bodies and would not work in an open catchment system, such as a river. None of the existing control tools can specifically target koi, so their use needs to be considered carefully with regard to potential impacts on New Zealand's native species

Current work programmes are focussed on exploring new and innovative control tools. This includes drone and eDNA surveillance and commencing a project for a species-specific virus.

Koi carp control tools - what's currently available and new tools being explored.

DOC's Biodiversity 2018 programme

This programme has $2.1 million allocated specifically to targeting freshwater biosecurity and now has an enhanced national programme focussing on priority freshwater pest plants and pest fish nationally.

The funding has enabled the establishment of new positions in freshwater biosecurity to increase staff numbers, has supported a range of eradication programmes and funded research projects to identify new monitoring, surveillance and potential control tools.

Waikato Freshwater Pest Programme

DOC and Waikato Regional Council have established an agreement to work together to manage freshwater pests, including koi. Although this agreement targets the Waikato region, the programme is linked with stakeholders across New Zealand with similar pest fish issues.

The agreement includes a Waikato coordinator role to drive the regional programme of work, maintain oversight across pest fish issues regionally and nationally and also pull resources together for future control programmes.

Related links

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Koi carp are an ornamental strain of the common carp ( Cyprinus carpio) native to Asia and Europe. This species is thought to have been imported into New Zealand accidentally in the 1960s as part of a goldfish consignment.

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NZ Geographic article about bow-hunting koi. Use for comprehension, deep reading.

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The war on koi

Invasive koi carp now writhe through wetlands from Auckland to Marlborough, displacing native species and destroying freshwater habitats. For 25 years, bowhunters in Waikato have ministered their own brand of pest control, the World Koi Carp Classic, resulting in prizes, and 70 tonnes of puréed fish.

On October 29, 1988, Dave Gousmett travelled south from Auckland to the Whangamarino wetlands, north of Huntly. He'd heard rumours of huge golden fish having infiltrated the area. An avid bowhunter, he thought he might have a go at shooting one. The day was overcast and still, with water levels high enough to flood parts of the Waikato. It was a perfect day for shooting fish.

Gousmett had a day's tour plotted out on advice of DOC staff. The second spot on his list was a submerged paddock on Falls Rd. It was here that he saw his first koi carp. Pretty soon he saw his second, then his third. There were dozens, bright-orange flecked with black, basking in shallow water.

Koi carp are thought to have been naturalised after fish from a garden pond were liberated into a waterway near Te Awamutu in the 1960s. For 20 years, they spread and bred, first coming to DOC's attention in 1983, with Gousmett and the bowhunters following a few years later. But it wasn't until the 1990s that the true extent of the problem was revealed.

Koi carp are now widespread in Auckland and Waikato and are spreading into Northland. They have been found in Whanganui, Hawke's Bay and Wellington, and illegally released in the Nelson/ Marlborough region too.

All morning, Gousmett fired and came up empty, the alloy target arrows bouncing off or breaking in the strong, thick-skinned fish. Finally, he came upon a large patch, and fired once more. Another miss, and the fish were spooked, fleeing up a stream. He took aim at the last fish in the school, fired-and hit. Three kilos of inedible ornamental koi carp was on the line, and a strange passion was lit among a small but devoted bunch of archers.

Gousmett has since made more than 450 trips down from Auckland to the Waikato wetlands to hunt the fish. He and other bowhunters love koi. "If you're a bowhunter, you like shooting your bow," he says.

With koi, you get to do that a lot. When hunting deer, you might fire two or three shots in a week. A good bowhunter can hit more than 100 fish in a single day.

While koi were still rare in the late '80s, in subsequent decades they've thrived spectacularly.

I stand alongside a small stream adjacent to Lake Waikare, near Huntly, and watch koi constantly for half an hour. They breach and wriggle muscularly upstream through the rapids. It's a spectacular sight, all the more so for the incongruity it represents-these fish are bright orange and yellow, striped and spotted and quite manifestly not from around here. I've seen them before, lazily meandering through ponds at fancy hotels. There they made sense. Here their presence is unnerving.

This invasive species-'pest fish', to those who work with them-is now the subject of intense efforts to control its spread, to purge it from conservation areas and give aquatic life a chance to revitalise there, away from the koi's suffocating presence.

The bowhunters-for their part-have expanded their hunt with the expanding range and population of their quarry, and decided to make a competition of it. The grandly titled World Koi Carp Classic (WKCC) was first run two years after Gousmett shot his first fish. The tournament has now become New Zealand's biggest bow-fishing event, and one of our nation's most bloody and bizarre sporting contests.

The tournament is now in its 25th year, and the aim has remained the same: to shoot and kill as many koi as possible. A relatively small number of bowhunters gather at Huntly each year and go mad with bows and arrows. Together they've claimed more than 25,000 koi. More than 70 tonnes of coarse fish. There are prizes for the biggest and smallest in various colours, and two categories for the benefit of the bloodthirsty: Team Weight, for heaviest cumulative catch, and Most Carp, for the sharpest-shooting individual.

On the first weekend of November, men gathered from around the country to take to the region's waterways with bows and arrows. While the number of participants was down somewhat on previous years when more than 100 took part, there were still more than 50 archers roaming the lakes and streams of the Waikato in boats and on foot, shooting fish.

Photographer Richie Robinson and I arranged to meet at the tournament's headquarters, the former Huntly railway station alongside Lake Puketirini, a former opencast mine turned into one of the region's few pristine bodies of water. We arrived at 8am and found not a soul. Bowhunters are solitary and competitive sorts-most had been up at dawn and off alone or in teams to prime locations they guard jealously.

Around the far edge of the lake we met up with the last to leave. Logan Cubitt and Jon Howard were gazing out to the water and prepping their gear. They make an odd pair. Cubitt is tall and in his late 20s. He got into bowfishing mainly as a "piss trip" with some mates. They drifted away, but bowfishing stayed with him. Howard is 14, a student at Tauranga Boys' College, and here with his father. He's solidly built and ghostly pale, only six months into archery but already possessed of his first big-game badge: 'daytime wallaby'. They agree to let the photographer and me tag along for the morning.

We drive north before heading back across the Waikato River near Glen Murray, then make a left through what looks like a private farm gate. The track deteriorates until it is barely a contour in the grass, shadowing a small tributary of the Waikato which flows from the north-western tip of Lake Whangape.

There's a rocky weir running along the boundary of the river and lake. The trio walk across, Cubitt striding confidently, pulling ahead, while Howard and his father linger gingerly. Towards the far edge, Cubitt pauses. In one smooth motion he draws his bow, aims and shoots. There's a flash of white, then a mighty stir.

He's nailed a five-kilogram white koi mere minutes into the morning. It's not long after 9am on a perfect day in the Waikato, and the omens look good for these young archers, and very bad for carp.

Then, for a long time, there's nothing. Howard wanders down the riverbank, firing dozens of times, always missing. He's shooting too often, and from too far off. Cubitt is far more circumspect. He has a very particular walking style: feet very flat, with weight on his heels. Long, slow, deliberate steps.

Koi have a bone in their skulls that is extremely sensitive to vibrations, hence they spook easily at human footfall. But for all his patience and experience, Cubitt's results are as poor as Howard's.

After an excruciating hour, Howard finally finds flesh, winging a rather miserable little goldfish-another invasive species endemic to the area. The pair give up, though Cubitt picks up another good-sized orange koi on his return journey. He tows his fish behind him on a rope hooked through gills to mouth. They trail over rock and grass and arrive grazed and dirty, with none of the reverence often reserved for edible fish. He smokes a couple of Dunhill blues while they weigh their meagre haul. Cubitt's are both in the five-kilogram range, while Howard's goldfish is a little under a kilo.

It flops around forlornly, and Howard bashes it with a club. A little too enthusiastically.

"Jon! You're going to reduce the weight of it if you take its head off," admonishes his father.

"I'm just going to squeeze the guts out," says Howard. He's keen to take out the 'smallest' category. Dad's not impressed. "You'll win fairly or not at all," he says sternly.

It's a disappointing start to the weekend. We'd heard about 25-kilogram grass carp, about water teeming with fish, about spawning events that turned the water bright orange. We'd been told about Kevin Low, a tournament legend with stamina to match his aim. He would run along the lakeshore, shooting as he went, leaving his partner to pick up the catch. Many of the WKCC's meticulous records for size, volume and total weight are owned by him or his teams. Low won Most Carp eight years in a row; his record weekend haul was 331 in 2006, when his team brought in a monumental 869 kilograms of carp-more than one per cent of all fish shot in the history of the competition. By one team, in one weekend.

[Chapter Break]

While bowhunting represents one method of control, science has presented another; a $250,000 project called 'Carpuccino', operated by Bruno David, a driven, passionate Australian freshwater ecologist. It consists of a clever trap and even cleverer 'digester', driven by geothermal bacteria, turning an environmental disaster into a neat environmental win in the form of organic fertiliser.

I head east across the Waikato, past Te Kauwhata to a smaller stream off another lake to check it out. Carpuccino is easy to find, at the end of a gravel road around to the western edge of Lake Waikare. I hop over a gate and stare through a chain-link fence at this contraption, at once ordinary and brilliant.

It features a one-way gate allowing koi in, but not out. They thrash about in a large basket adjacent to a raised conveyor. The conveyor leads to a log mulcher, the product of which flows in turn to a faded red shipping container.

David and his team will find six to eight tonnes of carp in the trap during spawning season. The pests are hoisted up from the trap in a kind of fish-execution elevator, which slides them down the chute to be mulched, and from there the pulpy mess heads into the shipping container. Inside, micro-organisms known as geothermal bacteria get to work.

They're brutally efficient. Within 48-72 hours, all that's left of the carp-known for their leathery skin and dense skulls-is a fine brown powder reminiscent of ground coffee in consistency, if not aroma.

Because the carp are swimming in the dairy-intensive Waikato district, they hold abundant nutrients. There's zinc, used to treat facial eczema in cattle. Potassium, to regulate their osmotic pressure. And nitrate, to aid bacteria in the rumen.These minerals are great for cows, but terrible in the water. Unless you're koi, that is. They thrive in adverse conditions. And as the water in the Waikato has degraded, the koi population has exploded.

Today, koi carp represent an estimated 80 per cent of the biomass in the Waikato's waterways, and experience on the five continents (only Antarctica is safe-so far) suggests once they're established, getting rid of them is all but impossible.

A mature female can lay half a million eggs at a time, and their population density is now so high that their average weight has halved since they were first found. They are at capacity for the ecosystem.

The biggest casualties of koi's bright, merciless march to dominance have been native fish and eels, whose numbers continue to drop precipitously.

You could forgive a passionate ecologist like Bruno David for being discouraged in light of this seemingly irresolvable downward spiral. Ever more intensive dairying degrades the water quality, the carp benefit, and their destructive foraging style exacerbates the turbidity. This further endangers native fish.

But David's an upbeat chap, in love with his work. He has big, wild dreams, and the ability to get them put into motion. Carpuccino is the wildest, and has the most exciting potential. His plan is to take Carpuccino's output and render it in tablet form. When placed underneath the native. trees his team plant on riparian margins, it has the effect of turbo-charging their growth and increasing survival rates.

It's an idea that excites the mind-taking a pest filled with excess nutrients out of the water, using it to create fertiliser that is then used to help return riverbanks to their natural state. This provides a habitat for birds and, eventually, improves the habitat for native fish too. Better yet, it has the ability to be fiscally neutral.

"I like the idea of creating a funding stream from the invasive fish," says David. "At no cost to ratepayers, we could run an invasive species control programme."

David calls carp "nutrient vectors"-big sacks of nutrient-rich biomass, swimming around. When they're captured and killed, that nutrient can be transformed from a 'problem' in one context into a 'solution' in another.

The prospect thrills him. "We're wanting to create a moralistic tablet from these unwanted invasive species that we can then use in the right context," he says. "We're taking nutrients from an area-the Waikato-where it's in excess, and putting it in the dunes, where it's poor today but in fact it used to be rich."

Such creative scientific thought, such knowledge of the ecosystem, such care over building something good from the carp problem. Ultimately, though, it involves the slaughter of fish in industrial quantities. And while David's fancy machine is a sophisticated, moral assassin, all around the Waikato that weekend, there were dozens of more primitive killers.

[Chapter Break]

The day after our mostly fruitless trip down to Huntly, Richie and I returned together to meet tournament organiser Allan Metcalfe, a bluff former dairy farmer with a thick grey-brown moustache, and his friend Philipp Loest. We arrived at Metcalfe's home a few minutes west of Huntly-an old farmhouse, unwanted by the company that bought his farm, perched on a hill overlooking Lake Waahi. Metcalfe is kept busy by turning his homestead into a convention centre and venue, with 1000 guests booked for various events through Christmas.

We drive down farm trails and spendthe next six hours wading through the wetlands around Lake Waahi. The lake is cut in two by a private road running between the coal mine and Huntly Power Station, with an underpass for swans-a legacy of the 'think big' era, says Metcalfe. "The swans never used it."

Despite the industry, the farming and the man-made intrusion into the habitat, down at the water it's serene. The lake surround is skirted in parts with trees and bush and looks healthier than much of the rest of the region's waterways. Still, Metcalfe ruefully recalls what's gone: the deafening chorus of frogs that used to accompany his time down here, and the freshwater shrimp his kids once caught.

It crosses my mind, briefly and uncharitably, that it's a little rich for a dairy farmer to be lamenting the loss of biodiversity in a lake which is bordered for long stretches by land his cattle once grazed. As if sensing it, he points out that he and his wife, Dawn-a fervent environmentalist-personally fenced the full seven-kilometre circumference of Lake Waahi, and says they farmed differently in his day.

"It's not just one thing that's harmed the waterways," he says. "I never used nitrogen. Nowadays, they just pour it on." Metcalfe is a different kind of farmer, from a different, fading era.

The shooting is slow this morning. The previous day, Loest snapped a string under the weight of the fish he was dragging, and still ended the day three fish behind Metcalfe. They pretend to be relaxed about their personal tallies, but I'm not convinced.

"You shot your three?" asks Metcalfe. "Can I start shooting yet?"

Loest goads him all day. "Allan was shooting here yesterday," says Loest when we arrive at the lake, "so there'll be a lot of wounded fish out there."

That's unlikely. Metcalfe may be older than 60, but he remains a crack shot. He turned to archery after a bad concussion ended his rugby career, and became good enough to represent New Zealand. He and Loest trade shots, hitting a koi every 15 minutes or so for a few hours. Eventually, appropriately, they end up even.

Metcalfe and I wait in the shallows while Loest lingers way out in the lake, on the other side of some trees. It seems he's determined to win. Half an hour later, he comes striding back with a good-sized yellow koi, unable to suppress a grin. That fish has won him the weekend.

Despite the infrequency of action-at least compared to the really hot spots they never showed any interest in moving to a different location. Waahi is familiar; it's koi bowfishing's spiritual home. The last evidence of that era is a shed with a peeling wooden sign reading 'The Koi Club' further around the shore. We stop there for lunch after finishing for the day. Inside, one of the windows has been smashed by vandals, but years' worth of records remain pinned to the wall.

The competing bowfishers all used to camp in the paddock behind the shed, have a big bonfire and get on the beers. Now the original crew are older, a little more restrained. But Metcalfe's got more fight in him than he lets on.

"I'll tell you what would really piss him off," says Metcalfe, while Loest takes a break. "If I were to go out there and shoot one now."

The thought proves irresistible. He sneaks off up the bay, and 15 minutes later, he's back-with one last fish. "I had to shoot him in the head because I didn't have my club," he says. The arrow is dead between the eyes-the hardest shot in bowfishing. It's sealed a draw. Loest smiles grimly.

[Chapter Break]

An hour later, we're back at tournament HQ at Lake Puketirini. For the first time, I'm witnessing the true nature of this competition-the bowhunting fraternity en masse. The participants are a mixture of slightly wild-looking men in their 30s and 40s, and a younger group who in bearing call to mind the taciturn survivalist set in the United States.

Nigel Mills is pale, freckled and very heavy, with a blue singlet on and dirty blond braids. He sits on a bench in the shade of the old railway station, waiting for the catch to come in-the first of a steady stream of fishermen that will flow through.

They're there to complete the process and turn to a remarkable piece of Waikato technology. Stormin' Norman is a sort of industrial-scale garden mulcher, a petrol-driven brute designed to mince halved sheep. It came from a ferret farm, and is named for the aged farmhand who first spotted it for sale. It eviscerates koi in a heartbeat and turns them into high-quality berley, for which demand has increased markedly since it lured in a monster snapper a while back.

There's a lot of it to go round-four and a half tonnes by the time the last fish are weighed in. It's a gruesome makeshift factory: there's an expanding queue of utes and trailered boats full of carp snaking out of the lot, bringing the fish in, to be counted, weighed and transferred into tubs. Each load is often 25 kilograms or more, and is hefted across the tarmac to a six-by-four-metre wooden pen lined with a large blue tarpaulin. A tractor with Stormin' Norman on the back is positioned over one end.

Berley customers take turns grabbing a tub, dragging it into the pen, then tossing fish after fish into the grinder. It makes a sound like a chainsaw running through live timber, disposing of a large koi in around a second. It's efficient, but not a pretty process. Everyone who pitches up for berley comes away flecked with fish guts.

Koi are particularly fragrant-part of the reason they're not considered edible, except in certain Asian cultures. We're less than an hour from central Auckland, but this scene is everything I love about rural life-an amiable, community-uniting massacre.

Near the end of the two-hour weigh-in, the heavy-hitters start arriving-all with boats, all with dozens of fish. First Martin Brennan and Theo Ryks, a trans-Tasman team whose small alloy vessel's hull is ankle-deep in fish.

Ryks jokes that he's "the last of the dairy farmers", and lives just up the road. Brennan wears trackpants and drinks beer. He's over from Australia especially for the tournament, both to see his mate Ryks and because it's not a pleasure available to him in his adopted home.

"Australia's got too many stupid laws," he says. "Every time I've tried, the cops have told me, 'You can't do that around here'."

In New Zealand, not only do our officials allow it, they endorse it. Three men with the nightmare job title of 'Partnerships Ranger' are here from DOC, which sponsors the tournament to 'raise awareness' of the koi situation. What exactly that awareness will do to help matters isn't made clear, and the department's stance towards the bowfishers differs from that of Bruno David. The ecologist finds the event's wanton slaughter both functionless from a control perspective (because it's geographically so widely dispersed) and morally troublesome. "It's not their fault," he says of the koi. "People need to have a certain level of respect."

There is little of that here this afternoon. The fish are pitched merrily from boat to tub to scale to tub to grinder with no great reverence. I find myself periodically dwelling on the emptiness of killing these thousands of fish, not for food and with no prospect of impacting on the unknowably vast population of the pest species.

I watch Ruben Hastings and Ben Passau-team 'Monsters Inc'-disgorge their mammoth catch, well over 500 kilograms of fish for the weekend, and it feels a little barbaric. Hastings is in military-style camouflage fatigues: a compact, wiry man in his early 20s with an enormous, unkempt beard.

"There was this tiny inlet we found," says Hastings of their epic, competition-winning haul. "It just opened up and carp were everywhere."

I have misgivings about this event, but I can't reconcile it with the affection I feel for this group-particularly Metcalfe and company. He, wife Dawn and a group of friends do all the heavy lifting for this peculiar event. They're incredibly hospitable and genuine, glowing with pride and pleasure for the tournament they've now run for 25 years. And while they and DOC make the right noises regarding containing the problem, privately they'll admit it doesn't even scratch the surface in terms of control.

The World Koi Carp Classic is better described as an event that unites an otherwise quiet and dispersed group of people. For one weekend a year, they come together, kill a bunch of carp and enjoy one another's company. For the Metcalfes, and the rest of the organisers, that's enough.

"We've really only done it because we enjoy doing it," says Gousmett. "And because people kept turning up."

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Invasive koi carp now writhe through wetlands from Auckland to Marlborough, displacing native species and destroying freshwater habitats. For 25 years, bowhunters in Waikato have ministered their own brand of pest control, the World Koi Carp Classic, resulting in prizes, and 70 tonnes of puréed fish.

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Attempts to create a mini England in the southern hemisphere drastically and irrevocably changed the New Zealand waterscape through the importation and release of exotic species for food, angling and attempted biological control.

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Northland example - watch to see a good explanation of why pest fish are a problem.
Question to consider: why would we value some fish over other fish? Can you think of any reasons?

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Species whose introduction or spread threatens biodiversity, food security, and/or human health and wellbeing.

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Species that have been brought to Aotearoa New Zealand by humans, whether intentionally or unintentionally.

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Refers to a species that naturally occurs in a place (e.g. Aotearoa New Zealand).

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The ecological zone located at the bottom of any marine or freshwater body like river, ocean, lake or pond.

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He momo kaikiko, he kīrehe te nuinga. Ko tā te konihi he whaiwhai, he whakamate, he kai i ētahi atu kīrehe. Hei tauira, ko te raiona.

A type of carnivore, in most cases an animal. A predator hunts, kills and eats other animals, for example, the lion. This is known as predation.

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Learn about how we keep Aotearoa safe from pest species (of all kinds!).

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New Zealand has a unique ecosystem. Our native species once thrived without any native predators. However, many introduced predators and pests arrived with humans, and threaten the survival of our native species and the success of our primary industries.

Biosecurity helps to prevent or reduce any damage caused by unwanted organisms.

What is biosecurity?

Biosecurity is about keeping New Zealand free of unwanted organisms and controlling, managing or eradicating them should they arrive in the country.

Biosecurity in New Zealand includes a set of measures designed to protect our country from the entry and spread of pests and diseases. Anything that is brought into New Zealand or moved around New Zealand has the potential to introduce or spread harmful pests and diseases, so biosecurity is everyone's responsibility.

Pests and diseases are a risk to:

the economy - our primary industry exports generate over 36 billion dollars each year

environment - New Zealand is an isolated island nation with unique plants and animals that have evolved over millions of years. Our biodiversity could be greatly reduced if certain pests and diseases enter the country

cultural and social values - pests and diseases could change the way we are able to use our environment, for example aquatic weeds could prevent people from using our waterways for recreation or for gathering food

human health - pests and diseases can impact on our health, for example bird flu and Ebola.

What makes a pest a 'pest'?

Plant and animal pests are species that have been introduced to New Zealand and threaten our native plants, animals and natural habitats. Plant and animal pests have become the greatest single threat to our native plants and animals.

Plant pests threaten our native plants by smothering, strangling or crowding them out. Eventually plant pests can take over our forests and wetlands. Many are also a nuisance to farmers, in home gardens and may cause health problems for some people. You can find out more about some common weeds here.

Animal pests threaten our region's native ecosystems, such as forests and wetlands. Some animal pests, such as feral goats and possums, destroy plants by eating their leaves, flowers or fruit. Other animal pests, such as stoats and rats, eat our native birds or their eggs as well as native lizards, frogs and insects.

Many animal pests are also a nuisance to farmers, in suburban gardens and businesses. For example, goats create erosion on riverbanks, and possums carry bovine tuberculosis (Tb). Bovine Tb is a disease that affects farm animals and threatens our export markets. You can find out more about animal pests here.

Pest fish also affect our waterways, such as lakes and rivers.

Some biosecurity threats that already exist in New Zealand include:

didymo

kauri die back disease

common and German wasps

introduced predators such as possums, stoats, ferrets, weasels, wild cats and rats.

Myrtle rust is a fungi which affects the Myrtle family including pōhutukawa, rātā, kanuka, manuka and feijoa and has just been found in Kerikeri in Northland.

How do you think you could help manage these threats?
The Ministry for Primary Industries manages biosecurity in New Zealand. Laws have been created to protect New Zealand from introduced pests and diseases. These laws include:

The Biosecurity Act 1993 - this law was a world first and was designed to protect both native and exotic organisms from the harmful effects of pests and diseases.

The Biosecurity Act was last amended (updated) in 2012 - there were a range of changes including stricter border controls, better pest management strategies and partnerships between industries and the government to help prepare and respond to biosecurity threats.

In 2016, the Biosecurity 2025 strategy was launched and includes the following:
- Biosecurity is everyone's responsibility - we all need to help keep harmful pests and diseases from entering or spreading in New Zealand.
- Using science and technology to prevent, manage and plan for biosecurity threats
- Strong leadership, training of biosecurity professionals and public education.

You can help

Keep a watch for anything that is potentially an unwanted pest or disease.

Report any sightings to the MPI free 24 hour emergency hotline 0800 80 99 66.

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New Zealand has a unique ecosystem. Our native species once thrived without any native predators. However, many introduced predators and pests arrived with humans, and threaten the survival of our native species and the success of our primary industries.

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Ko ngā tikanga, ko ngā whakaritenga hei ārai atu i ngā matū koiora me ngā rauropi ka whakararu, ka patu i te tangata me te taiao.

Procedures and arrangements that prevent biological substances and organisms from harming and damaging people and the environment.

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See how out-of-control goldfish can get! (American example)
Question: what do you think nature in New Zealand would look like if we didn't try to control the spread of invasive species?

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Goldfish 'army' takes over Colorado lake

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Warning: teachers/guardians may wish to exercise guidance around viewing this video. Canadian example.

Questions:

1. These are called 'goldfish', why do you think so many of them are no longer brightly coloured?

2. The narrator says they have removed 2000lb (pounds) of fish, can you work out  how much that would be in kilograms (kg)?
Hint - the formula will be:
weight(lb)  ÷ 2.205 = weight (kg)

3. These fish seem to live for a long time out of the water - can you think of some way to deal with lots of goldfish quickly so they don't suffer?

4. How do you feel about pest-fish control? Under what circumstances is it okay, or not acceptable?

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Goldfish in Taupō. Read this article closely and decide whether goldfish are considered a big pest in Taupō, or if (as they say) there are 'bigger fish to fry'.

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There's trout. There's koura. There's the occasional catfish.

It seems there's the occasional goldfish too, as a Taupo man discovered when he came across a 30cm-long dead orange fish floating in the lake at Two Mile Bay last week.

Local real estate agent and keen fisherman Grant Bayley was out for a morning walk when he came across the expired fish on the lakeshore, and he immediately worried that it might be a koi carp, a destructive fish species which degrades waterways.

"I saw this fish floating on the edge of the lake and I'm a pretty keen angler and I thought it didn't look right so I went and got my net and scooped it out," says Grant.

Grant asked a friend passing by to take a picture, before taking the fish home to call DOC. In the meantime his friend made contact with local environmental advocate Dave 'Didymo Dave' Cade, and Grant soon received a call from DOC freshwater ranger Brenda Lawson, who came to inspect the fish. Although she thought it was likely to be a goldfish, she sent it to a DOC fishery scientist in Turangi, who confirmed she was correct.

No action would need to be taken, although if it had been a koi carp, an incursion response would be mounted because carp are a pest fish that "we really don't want" says Brenda.

The Conservation Department regularly receives reports of goldfish in the lake, she said.
They were first introduced in the late 1800s by a member of the Armed Constabulary and are found throughout Lake Taupo but prefer the shallower slow moving waters at Motuoapa and Waihi, as well as the warmer geothermal waters on the lakefront. Their number have been affected by catfish, which invade the same habitat. They are not thought to compete with trout.

As well as Lake Taupo, goldfish are also in lakes Hinemaiaia A and B, Lake Rotongaio south of Waitahanui, and possibly others.

The biggest goldfish Brenda has seen was about 30cm long. Colours can range from orange to bronze but the main difference from koi carp is in the teeth, she says.

"They [koi carp] can kill off waterways because they have these very grindy teeth. They can dig into the lake edges and chomp up all the mud and get all the goodness out of it and then discharge the sediment into the water, which makes it cloudy. You get deoxygenation and all the native plants die off and the lake becomes really unhealthy."

Koi carp have ravaged the lower Waikato River and breed prolifically that's why it's so important to check, clean and dry gear between waterways, to avoid transferring koi carp eggs, Brenda says.

She praised Grant for notifying the goldfish catch and Grant in turn says he's hearted by the quick response from DOC staff.

"Lake Taupo is considered one of the best wild freshwater fisheries in the world and for it to become contaminated by foreign fish species or plant matter would be a disaster."

The Ministry of Primary Industries has a 24-hour number to report water or land-based pests or diseases.

MPI Pests and Diseases Hotline: 0800 80 99 66 or the Waikato Regional Council on 0800 BIOSECURITY (0800 246 732) .

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Local man finds 30cm-long dead goldfish floating in lake

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There's trout. There's koura. There's the occasional catfish. It seems there's the occasional goldfish too, as a Taupo man discovered when he came across a 30cm-long dead orange fish floating in the lake at Two Mile Bay last week.

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A fascinating read for older students (or educators), along with some hilarious photos of goldfish! Use for: discussing different values that people place on things (or fish) in different times or locations.

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"Oh, wet pet," American poet Ogden Nash wrote in pithy summation of the humble goldfish, whose habitat is, by tradition, a glass bowl anchored by the faux luxury of a gravel-bound ceramic castle. But the reality is more complex, suggests a new book by Anna Marie Roos, a professor of the history of science and medicine at the University of Lincoln, in England.

In , Roos fleshes out the cultural history of this seemingly ho-hum fish, painting it as both common and exotic, scientific research hero and environmental villain, and biogeographic success story. National Geographic spoke by phone with Roos about the fish more formally known as Carassius auratus.

As a science historian, you've written about esoteric subjects like 17th century mollusk expert Martin Lister. Goldfish seem comparatively banal. I gather there's a personal backstory.

I had a pet goldfish named Speedy. I was a geeky scientist at a young age and out of curiosity, touched him. He had really rough scales, so I poured hand lotion in the water to make his scales soft...

Yes. In part, I wrote the book out of guilt for Speedy.

Where do goldfish fit into the animal kingdom?

Goldfish are basically carp. The Chinese originally bred them to eat. Carp, which are normally grey or green, breed like crazy, and you get variations of colors and shapes. Nature plays around. They have a smattering of pigment cells that are red or gold. A mutation would have suppressed the grey pigment cells, allowing the yellow and red ones to be expressed. Humans took a mutation and made a species of them.

In China, the golden fish takes on religious overtones.

In about the ninth century, goldfish mutants, when captured by fishermen, were not eaten and [instead] released into Buddhist ponds of mercy in an act of fang sheng, or mercy release. The monks fed and kept them, so the fish were protected by not being in the open waters. Releasing an animal into such a pond of mercy was an act of self-purification, a good deed in the Buddhist religion, which becomes even better if the animal is rare, like a goldfish versus a common carp.

Let's follow in their wake as they circulate around the world. We start with China...

They are domesticated in China more than a thousand years ago and come to Japan around the late 16th century. They go to Europe and beyond as a pet and living ornament for aquaria and fountains via Macao. The first drawing of goldfish in England is by botanist James Petiver in 1711. By the 19th century, they are in the States and mentioned in 1817 in Webster's Dictionary.

Losing their mystique and exoticism along the way, no doubt. At one time, you write, the United States government gave them away.

In a publicity stunt, from 1884 to 1894, if you were a resident of Baltimore or Washington, D.C, and wrote your congressman, the U.S. Commission of Fish and Fisheries [today the National Marine Fisheries Service] would send you goldfish. Some 20,000 were given away each year before the program was discontinued.

Other suppliers took up the slack.

By the turn of the century, the Midwest had huge goldfish farms. Grassyfork Fishery in Indiana produced two million a year. Grassyfork was even a tourist attraction.

They also have a starring role in more than 40,000 scientific papers. What makes them a good subject for experiments?

One reason is that they are good at absorbing substances, so they are used in toxicity studies. In the 19th century, for example, they were used to study digitalis dosing. They can regenerate their optic nerve, so they're of interest in vision studies. Also, they have pretty good memories, and that makes them useful in psychology studies. Their sensitivity to sunlight makes them valuable for looking at skin cancer. They are a good animal model because they breed easily and are cheap.

There was a brief goldfish-swallowing fad. What prompted that?

Officially, it started in April 1939, when a Harvard freshman swallowed one on a dare. It largely died out later that year with World War II, as there were other things to think about. Any animal rights activist would be appalled. Animals are not meant for our entertainment. In 2012, a young girl in the United Kingdom was so disturbed about the custom of giving them away as fairground prizes, she started an online petition. In England and Wales, it's now an offense to give a goldfish as a prize to a minor.

Tell us about their troublesome side-goldfish as environmental villains.

Because they're carp, they're bottom-feeders and omnivores. They stir up the bottom of a pond or lake in search of prey, making the water turbid and likely to encourage algal growth. Because they are adaptable and can live in a wider range of water temperatures, they outcompete native species. In a head-to-head contest, trout will starve, goldfish will live. That's what happens when, say, a fisherman uses goldfish as bait, dumps them in a lake, and drives home. They breed and get big. So you get huge goldfish, like the foot-and-a-half one pulled out of Lake Tahoe. In 2015, 3,000 goldfish took over Teller Lake in Boulder, Colorado. The fisheries commission was ready to electro-shock the lake to get them out, when a big flock of white pelicans flew over and picked them off one by one.

Divine intervention? But you can't always count on a flock of pelicans to show up...

The fish has been listed as a nuisance in Colorado, Nevada, New York, North Carolina, Pennsylvania, Oregon. In Alberta, Canada, they have mounted a "Don't Let It Loose Campaign" and made it an offense to release them.

So we might say that the book, in line with Buddhist principles, represents your act of purification for Speedy. Do you think he's been vindicated?

Yes. How many goldfish do you know that have a book dedicated to them? If anything, I hope it makes people think about how we use animals as disposable commodities and the assumptions we make about their intelligence. Animals are not put here exclusively for human use.

This interview has been edited and condensed for clarity. Goldfish, from Reaktion Books, is available now.

Cathy Newman, a former editor at large at National Geographic, spent 14 years covering " The Immortal Corpse," published in the January 2019 issue of the magazine. She has written forThe Economist, the Wall Street Journal, and Angler's Journal. Follow her onTwitter.

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"Oh, wet pet," American poet Ogden Nash wrote in pithy summation of the humble goldfish, whose habitat is, by tradition, a glass bowl anchored by the faux luxury of a gravel-bound ceramic castle. But the reality is more complex, suggests a new book by Anna Marie Roos, a professor of the history of science and medicine at the University of Lincoln, in England.

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From pet to pest - short article to raise ideas about being good pet owners. May be worthwhile discussing Finding Nemo, and why flushing fish is not a good idea.

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One minute you're a pet goldfish, the next you're an aquatic pest.

That at least is the way it has turned out for 200 of the little fish that have been discovered living in Albert Town's Riverside Park pond.

The fish were spotted recently by a resident and their presence confirmed by a Department of Conservation (DoC) site visit that found a "large shoal''.

Conservation services manager Chris Sydney believes the goldfish were put there deliberately by someone emptying a pond or aquarium.

"It is exactly this sort of action that can spread nasty aquatic pests into waterways. Introduced weed and fish species ... can destroy the natural state of rivers, streams, lakes and other water bodies," Mr Sydney said in a statement yesterday.

"Not only do they spoil waterways, they can be very difficult and costly to eradicate."

DoC rangers will use an electric stunning device and nets to capture the fish next week.

Mr Sydney advised people to empty aquarium water into gardens rather than drains or streams and to clean fishing gear, boats and trailers after use to prevent the spread of pest fish and weeds.

An Albert Town resident next to the pond said yesterday some local children would be "devastated" the fish were being taken away, particularly the young boy planning to catch and sell them.

A DoC spokeswoman said "responsible" homes had been found for the goldfish, although it was likely fish in poor condition would be euthanised.

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How a pet goldfish can become an aquatic pest

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One minute you're a pet goldfish, the next you're an aquatic pest. That at least is the way it has turned out for 200 of the little fish that have been discovered living in Albert Town's Riverside Park pond.

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How DOC, Waikato Regional Council, and schools work together to remove pest fish.

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From NIWA Freshwater Invasive Species of New Zealand 2020

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The basics

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Author: Darren Stevens

First published in Aquarium World February 2014

brown bullhead © Noel Burkhead

Although many aquarists will have a common bristlenose or Corydoras catfish in their tropical tanks there are no native freshwater catfish (Siluriformes) in New Zealand. In contrast, our Australian neighbours have about 18 freshwater catfish species. We do however have an introduced species, the brown bullhead ( Ameiurus nebulosus) a stocky dark brown to greenish-olive catfish with 4 long whisker-like barbels, speckled with gold, pale olive, and grey. Brown bulheads are generally found in slow flowing, often weedy, streams and around the sandy shallow margins of lakes and lagoons. In New Zealand they commonly grow to 30cm but have been reported to grow to about 45cm and 2kg. They eat a wide range of food including freshwater insects, snails, crustaceans including koura, plant material, detritus, and small fish. They are a problem in our waters as they compete with, and eat, native species, including small native fish and koura. They also reduce water quality by stirring up mud.

In New Zealand brown bullheads are not well studied although they appear to be fast growing, reaching 8cm in their first year, and 33cm by their fourth year, and they may live for up to 8 years. They mature at age 2 or 3 (at about 180-200mm TL) and pair up and spawn during spring. They lay several hundred to over 6000 golden eggs in a shallow depression in mud or sand. Initially both sexes guard the eggs and young but as the young develop it is generally the male that will guard the young for several weeks.

Brown bullheads were introduced to New Zealand from California in 1877 and initially became established in the lower Waikato River and in Lake Mahinapua near Hokitika. They are very adaptable and are able to survive for long periods out of water. Unfortunately this makes them easy to accidentally transfer to new waterways in fyke nets or on boat trailers, and they are now reported from a number of waterways including the Whanganui River, Ruamahanga River, and Lake Taupo. At times they can very abundant with a single overnight fyke set in Lake Taupo catching 639 catfish. To help prevent further spread if you catch a brown bullhead you must kill it immediately. The penalty for possessing a live bullhead catfish is $750.

References:

McDowall, R. M. (1990). New Zealand Freshwater Fishes: A natural history and guide. Heinemann Reed, Auckland.

Brown Bullhead Catfish - Code of Practice Effective from 1 October 2007. http://www.fish.govt.nz/NR/rdonlyres/333F2B8C-6808-4DD7-868A-B7100F71DDE8/0/Brown_Bullhead_Catfish_Code_of_Practice.pdf

Barnes, G.E.; Hicks, B.J. (2001). Brown bullhead catfish ( Ameiurus nebulosus) in Lake Taupo. In: Department of Conservation 2003. Managing invasive freshwater fish in New Zealand. Proceedings of a workshop hosted by the Department of Conservation, 10-12 May 2001, Hamilton. xiv +174 p.

© This item may not be reproduced without written permission

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The brown bullhead - our very own catfish pest Author: Darren StevensFirst published in Aquarium World February 2014 brown bullhead © Noel Burkhead Although many aquarists will have a common bristlenose or Corydoras catfish in their tropical tanks there are no native freshwater catfish (Silurifor...

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Excellent video and article on catfish in Rotoiti.

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Site designed and developed by bka interactive ltd, Auckland, New Zealand (www.bka.co.nz)

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Containing the spread of catfish in our waterways

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A mix of history, korero about impacts, and kaitiakitanga. For more about 'Check, Clean, Dry', check the 'How can we help' column.

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Meet the Catfish Killers | nzherald.co.nz

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A catfish guarding its nest (outside NZ). Notice the elaborate nest and many, many eggs!
Questions:

1. Why do you think some fish lay so many eggs?

2. Do you think the person who filmed this likes catfish? What makes you think that?

3. If you lived in a place where catfish are native would you think about them differently?

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Old article (2001!), but raises questions about how we can control or remove pest species whilst benefiting society in other ways.
Question: Rawina says she would be thrilled to fish herself out of business, but this isn't always the case. Investigate how bounties have failed to control pest species. You could start here.

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By JO-MARIE BROWN

A "ticking ecological bomb" lies in Lake Taupo but one woman is determined to fish it out and make money while she's at it.

Rawinia Konui has spent 15 years battling to rid the lake of catfish, and has now begun selling the pest to Asian communities as a delicacy.

The "ugly" catfish were illegally introduced to the lake in the early 1980s and their numbers have exploded.

Dr Brendan Hicks, a freshwater fish ecologist at Waikato University, said catfish were a "ticking ecological bomb" and could seriously damage the native fishery if their numbers continued to swell.

Though the exact population size was unknown, hundreds of thousands of catfish were believed to live in Lake Taupo, feeding on native fish such as koura (crayfish), he said.

It was the sudden disappearance of koura in the 1980s that led Ms Konui's family to ask her to do something about the catfish problem.

Her great-aunt would fish for koura to take to church functions but by 1990 her fishing basket was dominated by "the ugly fish".

Anglers also grew concerned that catfish might be eating trout or stealing their food.

Ms Konui aims to turn a profit and create jobs while eradicating the pest. She has contracts to supply live catfish to markets in Auckland, Hamilton and Wellington and has signed a deal with a catfood cannery.

"From something very negative will hopefully come something very positive," she said.

"We'll help to conserve our fishery, which will help increase the quality of the trout as well as providing work for our people."

Profit was still a long way off, she said, but the 3000 catfish caught in the venture's first week would sell in Auckland for about $5000.

Ms Konui would be thrilled to fish herself out of business as eradication, rather than money, is her main focus. "I love native fish and I want to ensure that they're there for our great-grandchildren to enjoy."

Department of Conservation fishery scientist Dr Michel Dedual said catfish did not appear to be damaging the trout fishery yet.

The pest was mainly found in the Waikato River system. How it got into Lake Taupo was a mystery.

Dr Dedual said DoC would keep a close eye on the catfish population because the species might create problems in the future.

Waikato University student Grant Barnes, sponsored by DoC, studied the lake's catfish plague for his master's thesis in 1996. One night he caught 1300 in a single net.

Mr Barnes agreed that catfish could harm the environment. "They're the possums of the lakes in that they eat things they shouldn't."

Catfish had few predators and a female might lay 6000 eggs a season.

Though New Zealanders shunned them, catfish were considered a delicacy in southern states of America (where they originated) and Asia.

"They taste really yummy and Lake Taupo's such a clean, beautiful, pristine lake that the quality of the fish grown there reflects that."

A Chinese businessman was keen to export the catfish.

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Catfish hunter aims to cream a profit from pest

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By JO-MARIE BROWN A "ticking ecological bomb" lies in Lake Taupo but one woman is determined to fish it out and make money while she's at it. Rawinia Konui has spent 15 years battling to rid the lake of catfish, and has now begun selling the pest to Asian communities as a delicacy.

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Article about a catfish culling competition. This article is in pressreader and may or may not be available to all.

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PressReader.com - Your favorite newspapers and magazines.

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Connecting People through News. All-you-can-read digital newsstand with thousands of the world's most popular newspapers and magazines. Vast selection of top stories in full-content format available for free.

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Part 2 Number 4, 2005

Pest Fish by David Somerset

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Short article about eradication, and the need for ongoing monitoring.

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Rudd are native to Europe, Russia and central Asia, and were illegally introduced into New Zealand in 1967. The pest fish, which compete with native fish species and damage habitat, have spread around lakes, ponds and rivers throughout the North Island as well as Canterbury and Nelson.

They were first detected in Travis Wetland Nature Heritage Park by Christchurch City Council Park Rangers in 2008.

Council and Department of Conservation staff immediately targeted the fish in April that year, with help from Travis Wetland Trust volunteers.

On the first night of fishing 400 rudd were caught. High numbers were also caught in 2009 and 2010 using fine mesh nets, known as gill nets.

However, after four consecutive seasons of zero catches, Council staff now believe that close to a decade of hard work to remove the fish from Travis Wetland's central pond has paid off.

"We feel confident that we have reduced rudd's environmental impact to near zero," says Council Park Ranger John Skilton.

"It's great to know that all that effort we've put in over the years has been worthwhile. It's been a lot of hours in various weather conditions. If we hadn't started fishing back in 2008 our waterways would have been overrun with them within two or three years."

Just one fish can lay up to 50,000 eggs in spawning season. Although no rudd have been caught in the past four years, they are likely to be present in very low numbers and on-going monitoring is needed, he says.

"We have to keep going, we can't stop, but instead of up to six months of fishing each year we will just do one session in February."

Local ecology company Wildlands Consultants have independently verified Council monitoring and confirmed the zero catch.

It is hoped that bringing rudd under control will lead to an increase in the number and size of native fish species such as short-finned eel, inanga, black flounder, smelt, common bully and giant bully.

Members of the public should report any sightings of rudd to the Department of Conservation.

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Pest fish brought under control at Travis Wetland

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Rudd are native to Europe, Russia and central Asia, and were illegally introduced into New Zealand in 1967. The pest fish, which compete with native fish species and damage habitat, have spread around lakes, ponds and rivers throughout the North Island as well as Canterbury and Nelson.

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Pest fishing in the Travis Wetlands. A slow watch, but some cute songs that may inspire some song writers in students!

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Never dump unwanted pets of any sort in the wild - they can become pests and/or spread disease. If you can no longer look after your aquarium here are some guidelines:

Find someone else who would like to keep them as a pet (your local pet shop may be able to help), or;

Euthanize (kill) the fish humanely - best to approach a pet shop for this, too

Discard any weed matter in compost or general waste.

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The Department of Conservation has put a kibosh on "freeing" unwanted Christmas gifts into local waterways, saying it can wreak havoc on native species.

The release of aquatic pets, as well as water tipped into rivers and streams whilst cleaning, can impact native species significantly, DOC senior ranger Sue Moore said.

Once released, the pets can become extremely difficult to control, she said.

Commonly dumped pets were frogs, goldfish and red-eared slider turtles.

Many waterways in the Manawatu and Horowhenua were home to brown mudfish. Pets such as frogs prey on young mudfish and eat their food source.

"Our best hope is to prevent them from getting into our waterways to begin with. Then, we will have a better chance of stopping their spread," Moore said.

"While releasing a turtle or frog in the local stream may seem like the most humane way to deal with unwanted pets, it's illegal and damaging our waterways."

People should empty water from fish tanks onto land, away from freshwater, and plant life should be composted or disposed of in the landfill.

People were advised to return unwanted pets to a pet shop for re-homing or contact the SPCA.

Palmerston North business Wet Pets and Country Pets prefer to sell vouchers, rather than aquatic pets, when they were being gifted to others.

Senior sales assistant Eli Miller said gift vouchers were pushed to avoid people getting unwanted pets and to ensure they were suited to existing aquatic animals if they were to be sharing a tank.

"Generally we don't let people buy them as presents."

Unless it is a family member, such as a parent, people couldn't buy pets as presents unless the gift-reciever was with them, he said.

"Around Christmas is when people want pets, but this year was quiet."

People bought tanks as presents, rather than pets, with the idea of coming in after the holidays to choose the fish, Miller said.

Levin Pet World owner Lucy Carline said she did not think people would get rid of their pets because they pay a lot of money for them.

"They wouldn't buy them if they were getting rid of them."

Some fish cost $30, and added to the cost of tanks and equipment, it was not cheap, she said.

Aquariums that hold 215 litres of water could cost up to $600.

Carline said the number of pets sold before Christmas decreased as people waited until after Christmas.

"People are buying other things. We sell a lot of dog treats and toys," she said.

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Dumping unwanted aquatic Christmas gifts bad for waterways

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The Department of Conservation has put a kibosh on "freeing" unwanted Christmas gifts into local waterways, saying it can wreak havoc on native species. The release of aquatic pets, as well as water tipped into rivers and streams whilst cleaning, can impact native species significantly, DOC senior ranger Sue Moore said.

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Consider this article through the lens of the design/innovation process. Can students think of a problem they'd like to think of innovative solutions for in the freshwater space?

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The koi carp pellets are manufactured locally, and their ecological footprint compares very favourably to the often imported products they can replace. Uses mooted for the fertiliser pellets include as an additive to potting mix in native plant propagation, as pellets in new holes dug for dune plantings and as a potential alternative bait in rat and stoat traps. Two examples are outlined below.
Fertiliser for restoration planting
Dune ecosystems are some of our most threatened nationally, due to coastal development and other human pressures. Dunes are often nutrient-poor because of declining numbers of sea birds (their poo might smell gross, but it's a really important part of the nutrient cycle). Waikato Beachcare groups are heavily involved in recolonising denuded coastal ecosystems with plantings of spinifex ( Spinifex sericeus) and pingao ( Ficinia spiralis). Planting with tablets in dune ecosystems sees the nitrogen and phosphorous extracted from the lakes (stored in the flesh of the fish) deposited onto the dunes. Ordinarily, (usually imported) slow release fertiliser tablets are used in the planting holes to bolster early growth and improve survivorship. Some of these fertilisers are imported from a long way away and once they arrive at a planting day, they have a massive energy footprint. Council trials have demonstrated that the locally sourced koi pellets are at least as effective as the inorganic pellets (Bergin & Bergin, 2016), plus they come from just down the road and there are hardly any transport or production costs!

Dune vegetation - the front patch around the middle marker pole has been fertilised with Carp-N pellets.
Rat and stoat traps
The same pellets used in dune system plantings have also been tested as a lure for trapping other terrestrial pests when setting DOC200 traps. Pests such as rats and stoats spell disaster for our native wildlife and a crucial part of conservation in New Zealand is reducing pest numbers to give our native species a chance to bounce back. The incredible success of Hamilton Halo and other pest control programmes around the country are all pieces of the puzzle toward our national goal of Predator Free New Zealand by 2050. Pest traps are commonly baited with a wide range of goodies, like peanut butter, rabbit and egg - but could the pellets have the same or even better effect?

In a preliminary collaborative trial with the Dunes Restoration Trust of New Zealand and the New Zealand Landcare Trust, 50 DOC200's surrounding the predator proof fence at the new Rotopiko National Wetland Centre have been baited with alternating rabbit jerky/egg vs carp pellets to compare effectiveness. After four months the carp pellets have been performing particularly well on hedgehogs, capturing more than three times as many as the rabbit and egg option, and also performing slightly better for rats. Hedgehogs are hungry wee things and have a big impact on our native wildlife, so an effect lure for them is a great win.

How is it a win win?

This project is potentially game-changing for our struggling freshwater ecosystems, but it's more than just a solution to a pest problem. The project presents an opportunity for the council to sell the carp tablets to fund freshwater restoration projects such as targeted invasive fish removals, reducing the cost to rate payers, while providing communities with a locally-sourced, wholly organic fertiliser option - all while dealing to a very invasive species.

The project also represents an opportunity to collaborate with other organisations in the community, such as the New Zealand Bowhunters Society, who run the two-day World Koi Carp Classic in Huntly every year.

In recognition of the multi-dimensional merits of the council's approach, the project was the recipient of the 2014 Green Ribbon Award in the 'Caring for our Water' category and a KuDos Innovation Award for Science Excellence.

Carp processing. Photo: Waikato Regional Council

On the back of such success, one might expect the council to eagerly exploit the commercial merits of the concept. However, history tells us that an industry built on an invasive species creates environmentally perverse incentives that mean people fight to retain the invasive species to maintain industry, forgetting original intentions to eradicate them.

In recognition of this, the council intends to make the process cost-neutral at best and eliminate such incentives from increasing and not reducing environmental harm.

Attempts to commercially control carp over decades in other countries have also failed to contain the biomass or spread of this fish. This is primarily because the carp breeds so fast that the species is able to recover rapidly once local pressure is reduced (as catch rates fall below economically viable harvest levels). The council recognises this and considers that targeting priority catchments and maintaining pressure in specific localities can achieve a level of control that can reduce local impacts.

People can drop off fish they've caught for safe and ethical disposal at the council's 'Invasive fish recycling centre'. Contributors can rest assured that the material produced at the facility will be directed into positive environmental initiatives (e.g. as a replacement for synthetic high footprint restoration fertilisers). Additionally, the funding that could be derived from such sales has the potential to offset the costs of running the programme and potentially reduce, or with significant volume eliminate, costs of invasive freshwater species management for ratepayers.

This project began as one that focused on the removal of a single species, but the scope has broadened. Regional government has broad responsibilities in environmental management, and an effort has been made to 'zoom out' and consider how the successful trials might help solve other problems.

The pressure on freshwater ecosystems from invasive species is a serious issue throughout New Zealand and the world and the closed loop model employed by the council might well be easily exportable.

Back home in the Waikato, the successful roll-out of this programme spells the beginning of the end for carp and a much healthier future for our waterways and their native residents.

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The koi carp pellets are manufactured locally, and their ecological footprint compares very favourably to the often imported products they can replace. Uses mooted for the fertiliser pellets include as an additive to potting mix in native plant propagation, as pellets in new holes dug for dune plantings and as a potential alternative bait in rat and stoat traps.

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Mosquito fish (Gambusia affinis)

Gambusia affinis is small freshwater fish which was first released for mosquito control into an Auckland Botanical Gardens pond in the 1930s from a shipment from the Gulf of Mexico. They were also released in Northland, Taranaki and Wellington. They have now spread to many North Island waterways due to a natural spread and also by further illegal introductions. There are now populations throughout Northland, Auckland, Waikato, Bay of Plenty and Hawkes Bay and around Whanganui. Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Cyprinodontiformes
Family: Poeciliidae
Genus: Gambusia
Species: G. affinis
Binomial name: Gambusia affinis
Common names: Mosquito fish, Western mosquito fish, Gambezi, Gambusia

Gambusia affinis is now a pest fish which is negatively impacting our freshwater ecosystems as they are aggressive and attack native fish nipping at their eyes and fins. They also compete with native fish for food and have been known to eat native fish eggs.

Their habitat is the shallow margins of slow flowing ponds, wetlands and streams, particularly around aquatic plants. They can tolerate poor water quality, high salinity levels and a wide range of water temperatures.A single gambusia female produces several broods a year and around 50 offspring per brood. The young mature at six weeks old and are short-lived but breed rapidly and repeatedly enabling populations to build up to large numbers very quickly. Females give birth to live young. Consequently, only one pregnant female is needed to start a new population.

Gambusia affinis have a greenish sheen. Mature females reach an overall length of 7 cm and males are smaller at 4 cm. The female can be distinguished from the male by her larger size and a gravid spot at the posterior of her abdomen.

A female.

A male

Thanks to Wikipedia for text and information http://creativecommons.org/licenses/by-sa/3.0/

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t.e.r:r.a.i.n - taranaki educational resource: research

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T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

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Gambusia affinis is small freshwater fish which was first released for mosquito control into an Auckland Botanical Gardens pond in the 1930s from a shipment from the Gulf of Mexico. They were also released in Northland, Taranaki and Wellington. They have now spread to many North Island waterways due to a natural spread and also by further illegal introductions.

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In their native waters surrounding the Gulf of Mexico, gambusia are renowned for their ability to eat large numbers of mosquito larvae and are also commonly called mosquitofish. This ability led to their introduction into many countries where mosquitoes were perceived to be a problem, resulting in gambusia possibly being the most widespread fish in the world today.

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Ever thought of eating a mosquitofish?!

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He rōpū rauropi. He ōrite te hanga me ētahi āhuatanga o ngā rauropi o tēnā momo, o tēnā. Mā te ai o tētahi rauropi me tētahi atu o tōna momo e whakaputa uri ai.

A group of organisms that resemble each other and have common features. Each species can produce its own offspring.

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This is how we keep our awa, roto, and other waterways safe from the spread of pest species.

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MAF Didymo Programme Manager John Sanson and another man named Lance are at a lake, preparing to tow a boat behind a truck.

John: New Zealand has some of the most beautiful rivers and lakes in the world, and we need your help to keep them that way.

Lance: One way that freshwater pests can be transferred between waterways is on recreational items that you use in the water - everything from boats to boots. And once these pests are in the water they can have a detrimental effect on wildlife in our rivers and lakes and the quality of the recreational experience our waterways offer.

John: Because it only takes one pair of tramping boots or a wet lifejacket to give a hitchhiking freshwater pest a ride to a new location where it can establish and cause damage.

[Card: Protect our fresh waterways from pests. Check, clean, dry - everywhere, everytime.]

Lance: Now John deals with pest species in our waterways, and he's seen some of the harm they can cause. Now we're talking about didymo or what some people call rock snot, aren't we?

John: Not just didymo, Lance. That's had a high profile in recent years, but there are plenty of other pests invading our fresh waterways.

[Underwater video of each pest is shown as John describes it.)

Lagarosiphon is a fast-growing freshwater weed. Grows up to 5 meters tall forming dense mats which block waterways and displace native plants. It's a major problem in hydroelectric dams, and can block irrigation and drainage systems.

Hornwort is found in still and flowing waters growing to depths of 16 meters in clear, deep lakes. New plants can form from each piece of the easily broken stems and its dense growth crowds out native species.

Hydrilla is an oxygen weed. They can grow up to 9 meters tall in still or slow flowing freshwater. It's spread mainly through stem fragments which are easily transported to other waterways by machinery, boats, trailers or nets. At present it's only found in 4 Hawke's Bay lakes, but once established is virtually impossible to get rid of, once again forming dense mats which clog waterways.

And of course as we mentioned at the start there's our most invasive algal - didymo. In bloom it forms thick brown mats that smother rocks, submerged plants and other materials. It can clog irrigation and hydroelectric systems, and frankly it's an unsightly mess that can seriously harm the enjoyment of activities such as fishing and boating.

Lance: Now that's just a few of the main pest species we're up against. But where they do establish, everyone has a part to play in ensuring they don't spread, spoiling our fishing, our swimming, our tramping - anything that people enjoy doing on the water.

But if someone's out and about traveling between different waterways how do they know which ones have pests and which haven't?

John: Sometimes it's impossible to tell just by looking. So the best idea is: simply to treat all water you've just left as if it does have pests, and all water you're entering as if it doesn't.

[Card: Treat all water you've just LEFT as if it DOES have Pests, and all water you're ENTERING as if it DOESN'T.]

Lance: A nice simple rule of thumb, and it's pretty simple to remember what to do after you've left the water too.

John: Yup. The Check, Clean, Dry programme was established when it was realised just how quickly didymo was spreading. And it's still the easiest and most effective way for anyone to stop didymo and other freshwater pests in their tracks.

[The Check, Clean, Dry - Everywhere, Everytime logo is seen over video of people jetboating, kayaking, fishing, and hiking.]

[John and Lance are seen looking over the boat and all its gear, including the anchor and chain, propeller, fishing rod, and tow hook-up, and throwing away plant material they find.]

Lance: Ok - so first up - before you leave a river or lake check anything that's been in the water - your boat, fishing gear, vehicle, boat trailer, boots - anything - and remove and leave any debris at the site - not back in the water or down the drain. That's not going to help.

But hold on. If we're talking about things too small to see, how can we check for those?

John: Well no we can't. We're just starting by removing anything we can see which could be a pest or harbor microscopic pests like didymo.

Lance: And are there any things that need particular attention?

John: The underside of vehicles and tyre wells are one, inside your boat or kayak, swimwear and towels, and water toys like lie-lows or inflatable dinghies.

[Lance and John look in a wheel well of the truck, feel around the inside of the boat, and shake out a towel.]

Lance: Alright, you've checked and you've removed any obvious visible debris from your equipment, your vehicle, your clothing.

Now you clean it, and you can do that here or at home. Just so long as it's clean before using another waterway. And we're not just talking a hose-down with water, are we?

[John brings a bucket, bottle of dish detergent, scrub brush, sponge, and measuring cup.]

John: No, that's right. Water by itself won't kill pests.

Cleaning must be done with a solution of water and 5% of a suitable cleaner like dishwashing liquid, salt, nappy cleaner or antiseptic hand cleaner. These are all items that can be found at your local supermarket or your home.

[John measures out 2 cups of the dish detergent.]

Now a 5% mixture is 500ml or 2 cups of the cleaner with water added to make 10 litres.

Lance: And how accurate do you need to be?

John: As long as the mixture is at least 5% cleaning solution that's all you need to worry about. You can't overdo it when it comes to the effectiveness of the solution.

Lance: So if in doubt, err on the side of caution.

John: That's correct. And we also need to think about the environment. So we recommend using biodegradable cleaning products wherever possible. And it's also important to make sure that your wastewater doesn't dump directly into a drain that leads to a waterway, or a waterway itself.

Lance: All items that have been in contact with the water have to be thoroughly cleaned, and there are several ways to kill didymo. So it's a matter of choosing the most practical treatment for your situation, as well as one that won't adversely affect your gear.

[Lance and John clean various equipment. A lifejacket is shown being submerged in a bucket of sudsy water. Lance sprays cleaner on the reel of a fishing rod and wipes it with a dry cloth. A coiled rope is submerged in a bucket of sudsy water. John sprays cleaner on the tire of the boat trailer and inside the wheel well. A sudsy scrub brush is used on the side of the boat. John scrubs the bottoms of waders with a brush before submerging them completely in a bucket of sudsy water.]

John: Hard surfaces can be sprayed and scrubbed with the solution, while absorbent items like ropes, mats, life jackets and boots should be soaked and scrubbed, all for at least one minute.

Lance: Cleaning the inside of vessels is almost more important than cleaning the outside. Don't neglect areas like carpets and mats, bilges and anchor ropes.

John: And just as importantly, you must clean boots, life jackets, water toys or other gear. And remember - anything that's been in the water must be cleaned.

Lance: Now you might think it's not practical to be carrying cleaning solution around with you if you're out, say, tramping and need to clean your boots. Obviously you're not going to have a hose and bucket with you.

John: Well no. But you could carry a plastic bag with sufficient cleaning solution already in it and simply add the required amount of water from the waterway to clean your boots in.

[A boot is submerged in a plastic zipper bag with soapy water. The bag is closed and swished around to cover and fill the boot with the solution.]

Lance: You'll have to leave any rinsing off until you enter the next waterway where the cleaning solution will wash off. Don't rinse your gear in the water where you've just left.

Now there will be times when cleaning just isn't practical. So the next important step is drying.

[John dries the inside of a kayak with a towel. Lance dries the reel of a fishing rod with a cloth. John runs his hands over the kayak, straps and paddles to make sure they're dry.]

John: Drying alone will kill didymo, but even slightly moist didymo can survive for months. So to ensure the didymo cells are dead by drying, an item must be completely dry to the touch inside and out and left to dry for at least another 48 hours before using back in the water.

Lance: Planning your trip carefully could also help you avoid spreading freshwater pests. For example using only one waterway per weekend will enable enough time between trips for most of your equipment to be completely dry.

However you will have to clean anything made from absorbent material, like life jackets and boat carpets.

John: That's the minimum requirements for protecting our lakes and rivers from the spread of freshwater pests.

Lance: Yeah, it's not comprehensive and there's more info on the MAF Biosecurity New Zealand website, including more specific cleaning instructions for everything from gravel extractors to whitebait nets. Even pets.

John: Ideally you'll check, clean, dry every time you leave a river or lake - a bit like putting on your seatbelt every time you drive.

[Lance and John get in the truck and put on their seatbelts.]

Lance: And by ensuring you check, clean, and dry when you move between waterways you're playing a valuable role in protecting our rivers and lakes now and for future generations.

[The truck drives away.]

End title: MAF Biosecurity New Zealand logo. New Zealand. It's our place to protect. www.biosecurity.govt.nz

Thanks to:
Environment Bay of Plenty
Fish & Game New Zealand
Ian Gear

The Check, Clean, Dry programme is a partnership between the Department of Conservation, regional councils, industry, iwi and the community.

[End of transcript]

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MAF Didymo Programme Manager John Sanson and another man named Lance are at a lake, preparing to tow a boat behind a truck. John: New Zealand has some of the most beautiful rivers and lakes in the world, and we need your help to keep them that way.

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River, stream, flowing waterway.

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He rauropi orotā, arā, he rauropi patu i rauropi kē. Ka kīia ngā riha kua kawea mai ki Aotearoa i whenua kē, he riha rāwaho.

An animal or insect that has been introduced to New Zealand becomes a pest if it has the potential to cause significant national economic, environmental or cultural effects. In their home environments overseas, these organisms often create no problems.

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Lake, wetlands, swamp, settled or very low flow waterways.

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Ko te matatini o ngā ira, o ngā momo, o ngā pūnaha hauropi i tētahi wāhi.

Biodiversity is short for biological diversity. It describes the variety and diversity of all life on land, in fresh water and the sea. This includes ecosystems and the genes they contain.

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He mea ora. Koia nei ngā tukanga me ngā mahi matua a tētahi rauropi: ka kai, ka tukupūngao, ka tukupara, ka tupu, ka urupare ki ngā momo whakakorikori, ka nuku, ka whakaputa uri.

A living thing. An organism performs the following functions: it takes in nutrients, it respires, it excretes waste, it grows, it responds to stimuli, it moves, it reproduces.

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What to do if you find a freshwater pest?

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What to do if you find a freshwater pest?

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1. Use the Freshwater Invasive Species of New Zealand guide to identify the potential pest, its known distribution and information on its management status.

2. Document your find by noting exact location, date and photograph of the pest.

3. Photographs can be sent to NIWA Email: enquiries@niwa.co.nz for identification.

4. If possible, collect a pest sample. Invertebrates and small fish can be preserved in 70% alcohol, with larger fish stored in a freezer.

5. If the pest is managed for eradication or exclusion in your region by MPI or DOC report it to the pests-and-diseases hotline on 0800 80 99 66.

6. Similarly, for pest species not in the guide, report to the pests-and-diseases hotline on 0800 80 99 66.

7. If the pest is managed for eradication or exclusion in your region by a Regional Pest Management Plan contact your regional council biosecurity section

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Image credit: Wikimedia Commons

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Leuciscus idus

Origin: Europe
Introduced: 1985
Reason: fishing

Habitat: Orfe prefer slow-flowing waters in rivers and lakes.

Max Size: typically 45cm

Orfe breed rapidly, and don't have natural predators in New Zealand. As carnivorous (meat-eating) fish they can directly impact native animals as well as competing for food sources.

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Image credit: Christopher Caine

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Perca fluviatilis

Origin: Europe
Introduced: 1860s/70s, to Canterbury, West Coast, Wellington, Whanganui & Taranaki
Reason: fishing

Habitat: lakes, ponds, wetlands, slow-moving rivers.

Max Size: typically <40cm, 2kg

*Perch form the basis of a sports fishery, and are managed by Fish & Game (look back at 'when is a pest not a pest?'). In spite of this, due to their impact (below), appearance of Perch into new areas would be concerning.

Perch have a large impact as they eat many native species. Perch larvae (young) feed on zooplankton (tiny animals); mid-sizes feed on benthic invertebrates (things without spines!) including kōura; adult diet may include other fish. Lakes with perch have fewer bullies, galaxiids and smelt (all native fish) compared with lakes without perch.

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Image credit: Sjaan Bowie | DOC

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Tinca tinca

Origin: Europe
Introduced: 1867
Reason: fishing

Habitat: Shallow, still waters with plants/weeds.

Max Size: 70cm
*Tench form the basis of a sports fishery, and are managed by Fish & Game (look back at 'when is a pest not a pest?'). In spite of this, due to their impact (below), appearance of Tench into new areas would be concerning.

As benthic, carnivorous fish, tench may contribute to reduced water quality by stirring sediments and altering food webs.

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No recent records.
From NIWA Freshwater Invasive Species of New Zealand 2020

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From NIWA Freshwater Invasive Species of New Zealand 2020

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From NIWA

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From NIWA Freshwater Invasive Species of New Zealand 2020

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Gobio gobio

Origin: Europe
Introduced: first detected in an Auckland pond in 2004; eradicated
Reason: possibly for coarse fishery

Habitat: Lakes, reservoirs, ponds, wetlands and the still-water habitats of rivers and streams.

Max size: 21cm (from overseas examples)

The gudgeon is primarily a benthic (bottom feeding) carnivore, feeding on things that live in silt and sand. It may therefore compete with native fish for food and affect water quality in lakes and ponds.

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No recent records.
From NIWA Freshwater Invasive Species of New Zealand 2020

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Why would we want people to dispose of some things in certain ways? Think about the bins you put out at home:

Would you want the things in your home bins out in the environment? Why, why not?

When people dump rubbish in reserves and natural places they can cause pollution, encourage invasive (pest) species to thrive, and completely change ecosystems.

How could you communicate the importance of disposing rubbish appropriately?

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Video credit: A Siciliano | DOC

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Video credit: A Siciliano | DOC

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Brown bullhead or Catfish, Ameirus nebulosus (1)_o2

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Working together to keep koi carp out of a vulnerable environment. What other ways can students think of to exclude unwanted fish?

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Date: 21 June 2021

The barrier - at one of Waikato's most important freshwater ecological restoration projects - results from the Living Water project, the conservation partnership between Fonterra and DOC.

Koi carp are an introduced pest fish resembling giant goldfish and are widespread across the Waikato. An unwanted organism and noxious fish, koi are a serious ecological threat to the health of freshwater ecosystems.

The Lake Ruatuna grill barrier is designed to prevent access of adult koi carp upstream and serves as a final barrier between the lake and the pest fish during flooding events. The grill bar has spacings of 30mm allowing movement of native fish like tuna while also preventing adult carp passage.

Dion Patterson, DOC's Waikato Peat Lakes Site Lead, says there are limited options available to manage koi carp, and barriers act as a last line of defence to help control the spread of this pest fish.

"Koi are like the possums of freshwater," says Dion Patterson. "They're very hard to eradicate and are highly destructive. They feed like vacuum cleaners, sucking up anything in their wake and blowing out anything they don't eat - which isn't much."

Koi feed on insects, fish eggs, small fish, plants and almost any other organic matter. Their manic feeding stirs up the bottom of waterways, further degrading water quality. And unfortunately, koi thrive in degraded water.

"Koi carp have not been detected in Lake Ruatuna so maintaining this 'koi free' status is a priority for this site."

Catfish, rudd and goldfish are present in the lake and the ongoing control through net fishing is intended to reduce their numbers. The work of staff involved in pest fishing at Lake Ruatuna acts as a surveillance should koi somehow find their way into the lake.

The design, consultation, consenting process and construction has taken several years and water levels at the outlet had to be suitable for installation.

"The design and functionality of this trap looks great, and we are thankful to the expertise consultant John Gumbley has in this field. The trap will require ongoing checks for blockages and potentially weed clearance," says Dion Patterson. "Maintenance will be scheduled as part of regular predator trapping lines DOC Rangers and volunteers do around the lake."

Koi must be killed immediately if caught. Check, clean and dry all gear that comes into contact with water when moving between waterways to prevent the spread.

Contact

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Pest fish barrier helps control spread of koi carp at Lake Ruatuna

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Date: 21 June 2021 The barrier - at one of Waikato's most important freshwater ecological restoration projects - results from the Living Water project, the conservation partnership between Fonterra and DOC. Koi carp are an introduced pest fish resembling giant goldfish and are widespread across the Waikato.

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It's a long listen, but a fascinating insight into why Stewart Smith spent decades releasing exotic fish into New Zealand waterways.
Great for those wanting a bit more background (maybe on a bus ride to a fieldtrip?!). Good trigger for discussion of rights, law, and changing norms.

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Between the 1960s and late 2000s Stewart Smith went on a one-man crusade, releasing thousands of invasive fish into New Zealand's rivers, lakes and streams.

One kind of fish he introduced is now so widespread it's been declared an "acclimatised species", meaning the authorities have basically acknowledged it is impossible to remove it from the wild.

"The amount of damage he did was incalculable," says science journalist Charlie Mitchell, who wrote a feature on Smith for Stuff.co.nz.

"He could be positioned alongside the people who released stoats and weasels and ferrets in New Zealand," says Bryan Winters, who wrote an authorised biography of Smith entitled That Pommie Bastard.

So who was Stewart Smith?

He was a devout communist with a stubborn streak a mile wide, a conspiracy theorist who spent years locked up in a conscientious objectors camp, and an environmental imperialist dedicated to the cause of "improving" recreational fishing in New Zealand.
Subscribe free to Black Sheep: Apple Podcasts, RadioPublic, Spotify, RadioPublic or Stitcher.

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Between the 1960s and late 2000s Stewart Smith went on a one-man crusade, releasing thousands of invasive fish into New Zealand's rivers, lakes and streams. One kind of fish he introduced is now so widespread it's been declared an "acclimatised species", meaning the authorities have basically acknowledged it is impossible to remove it from the wild.

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Meet the Locals: Pest fish (general introduction)