The last stand of the monster koi of Kāpiti

Department of Conservation —  13/07/2022

By Rob Cross, Ranger and Koi Hunter

After weeks of searching Kāpiti waterways, I finally found it.

It lived in a private pond the size of a football field, fed by the Mazengarb Stream in Paraparaumu. A neighbour said she’d seen it twice in five years, and each time was a shock, considering how massive it was. Other neighbours had tried to catch it with rod and line, but it eluded them for years. I chatted to the son of the pond’s owner who said it was about a metre long, and he showed me a blurry phone video, its back humped out of the water, surfacing like the mythical Loch Ness monster.

This koi carp was a legend among locals.

Another neighbour said he lived near the pond since he was a kid. There were always koi in the pond, he said. Though people had tried to get rid of them, there was at least one left, and this sole survivor was a real monster.

Koi out of water – but not the monster koi. 📷: Sjaan Bowie

The white (and gold and black) whale

Koi carp are terrible pests. Basically, they’re pond possums, an introduced menace whose feeding and breeding trash aquatic ecosystems and destroy biodiversity.

When koi feed, they stir up the bottom of ponds, lakes, and rivers, muddying the water and destroying native plant and fish habitat. They’re like vacuum cleaners, sucking up everything and blowing out what isn’t wanted. Aquatic plants are dislodged in the process and are unlikely to re-establish. They eat pretty much anything, from insects, fish eggs, and other fish’s juveniles, to a diverse range of plants.

Koi carp cause habitat loss for plants, native fish, invertebrates, and waterfowl. They can also worsen river erosion by undermining banks as they feed. They have ravaged the Waikato River catchment for decades, reaching densities measured in tonnes per hundred metres. DOC has long run a national programme to ensure koi and other pest fish, such as perch, gambusia, tench, and rudd don’t do the same elsewhere, and we’re still committed to that.

As part of the control programme, another ranger (Lisa Clapcott) and I surveyed Kāpiti waterways, following up survey and control work done between 2005 and 2009. Back then, koi were found in many local ponds and in the Waikanae River catchment, and attempting eradication took a lot of work.

I came to this pond because the field notes from that programme said there were koi here. They caught several but missed one.

And here it was, immense and old, like Ted Hughes’s pike, stunned by its own grandeur. And here was I, not angling like Ted, but crouched low on the bank with a spear in the water, the hair on my head frozen like his.

Ahoy, a Koi

If this was the one they missed, it was more than 14 years old. That explained its size; they grow up to 75cm and 14kg in Aotearoa. The history of catch attempts also explained its circumspection; I’d tried with corn and bread the previous day and it failed to show. But I wasn’t going to be outsmarted by a fish, so this time I was well-hidden.

The fish appeared after an hour, nosing slowly along the berley trail carried by an outflow beside me. It stood off for half-an-hour, watching, then made two slow passes a couple of metres out. At this point I thought I’d been spotted, as the carp took fright and swam off. I tried more berley. Five minutes later, it was back, nosing along the trail.

This time it came in close. In Asia, koi are revered for their beauty, and it was clear why. This was a huge koi carp, golden with black splotches, iridescent scales overlapping in shimmering rows. Out-sized, bell-bodied, standing off warily from the berley near the shore, where incautious eels writhed and twisted right in front of the spear.

In Asia, koi are revered for their beauty. 📷: Astrid Van Meeuwen-Dijkgraaf

The Needs of the Many

One of the conundrums of conservation work in Aotearoa is that people who’ve loved nature and animals all their lives, and who’ve dedicated themselves out of reverence, come time and again to moments like these.

A friend of mine, a venerable old conservationist and winner of an ‘Old Blue’ award, is the follower of an Indian guru. On offering himself as a disciple, he told the guru that though he was a vegetarian, and tried strictly to observe the guru’s precepts, he nonetheless killed pest animals to protect native wildlife.

The guru excused and accepted him, saying the killing was for a higher purpose. I hoped to be excused in the same way as I held the sling spear under full load. When the carp swam broadside, I let go.

The multi-pronged spear hit hard but wasn’t designed for a fish of this size. The carp, stunned, stayed still until dragged to the surface near the bank. Just as I felt it’s full weight, it came back to life, thrashing, and broke free. In desperation I jumped in and grabbed it, but fish in water are like bars of soap. The carp slipped my grasp and darted away, leaving a crooked trail of shining scales hanging in the water, and bright clusters of the same impaled on the spear.

I returned the following day, with another ranger and a better spear. We looked, and we tried berley for hours, but saw nothing. Hard to blame it for not showing up, to be honest, and by the end we were convinced the locals were right; there really was just one gargantuan carp in the pond. For the next week I dropped in every few days to see if the fish was there, dead or alive. And I thought a lot about it, as you do when things go wrong, especially when living things are involved. The fish was a pest, and killing it would be a win. But we wanted it to be quick and clean, and I didn’t even know if the spear has succeeded in mortally wounding this glittering giant.

Impression of the monster created by artificial intelligence

A Bittersweet Victory

Ten days later there was torrential rain, and Lisa suggested we have another look. When the pond’s owners saw us pull up, they came running.

“You killed it! You killed it!” said the son, not angry, but congratulatory. After the rain he’d seen the fish upside down in the stream. He thought it had washed away through a culvert. The stream ran through thick vegetation behind their house, so we thought we’d take a quick look in case it was stuck in overhanging branches.

An appalling stench led us to the carcass, snagged on a log mid-stream. The majesty was gone; the gleaming gold colour had faded to a sickly white, and the eels had had a go at whatever they could get their needle like teeth into. We took pictures for the record and loosed the remains from the log. The carp’s body started breaking up soon as it was freed.

It wasn’t this animal’s fault that it had to be removed; despite all its grace and resilience, it was never supposed to be there in the first place. Introduced species pose huge risks to New Zealand conservation, especially when they occupy niches that our native species aren’t equipped to handle. While I know my actions were justified and will help safeguard New Zealand’s biodiversity, it was still an ignoble end for a creature put somewhere it shouldn’t have been.

By that stage, well into the job, this was the only koi carp we’d seen. The rangers of a decade ago had indeed done a thorough job, and this last holdout may have been, as Lisa jokingly said, the last koi on the Kāpiti Coast.

Let’s hope so.

Not the monster, but a decent sized koi carp. 📷: Nadine Bott

15 responses to The last stand of the monster koi of Kāpiti


    In terms of eating perch, koi, carp etc, we have tried at least two of these fish – thrown out almost immediately, I can tell you. Mud fish! Tasted like eating from a blooming rubbish bin . . . A local said they had used the dead fish as fertilizer in the garden, but they had some weeks of stinky smell before it was almost gone. But he could not say if it was any good for his garden in Menindee. I suspect that it would need a lot better ‘feeding of the ground’ to get a good crop as the sand/soil/clay mixture was really not too good at all.


    We have seen the carp in the Menindee Lakes dam wall – trying to crawl up the wall in a vain attempt to get further upstream into Lake Pamamaroo, then the Darling River itself. Fortunately, this did not happen, but thousands of fish dying at the dam would have smelt just a little off to say the least!


    Well done persistence pays.


    I’m pleased that the writer of this story wrestled with his conscience, but in the end that didn’t help this poor animal (which did die a pretty awful death by the sounds of it). Hope it was ‘worth it’. Our species (easily the most destructive on the planet, but the only one given a free pass) has a long history of ‘getting it wrong’ in our interactions with the natural world, and it seems like dangerous arrogance to assume that somehow, nowadays, we are ‘getting it right’. Too many vested interests involved.


      I’m struggling to see what your point is. We shouldn’t try to rectify the mistakes of the past when dealing with invasive species? How would that help the indigenous fauna and flora that continue to be affected by their presence?

      You’re allusion to ‘vested interests’ seems somewhat cryptic as well.


    Great story, beautifully written


    Rob, your statement “…other pest fish, such as perch, gambusia, tench, and rudd don’t do the same elsewhere,” implies that two nationally acclimatised sports fish species, tench and perch, are pests with the potential to cause the same level of environmental harm as koi. This is knowingly incorrect and unfair on licensed recreational anglers. It also undermines the good work Fish and Game has done in recent years to popularise sports fish species other than trout and salmon.

      Michael Gee 15/07/2022 at 8:34 am

      Well, tench and perch do cause problems for indigenous species which is why Fish and Game Councils encourage the fishing of them in places they currently exist, and do not allow them to be fished if these two species are released illegally into new areas.


        I don’t disagree, Michael, all exotic species have some degree of impact on the native environment and do need to be contained. I guess a good analogy is that not all the exotic plants we have in our gardens will automatically behave like old man’s beard if they escape into the wild.
        I also agree with the absolute prohibition of illegal introductions, and there are severe penalties for anyone found responsible. Banning angling seems like a helpful deterrent but it needs to be applied pragmatically so that we don’t just remove the responsible eyes and ears from the bank and make it easier for the perpetrators to go unnoticed.


      Perch in particular cause massive amounts of ecological damage in NZ across multiple levels of the food web. As juveniles their feeding on zooplankton can knock that level of the food web out of whack resulting in phytoplankton blooms, while larger adults can devastate native fish populations via predation.

      Just because the mechanism of their ecological effects differ from those of koi carp is no reason to minimise their level of environmental harm.


      Unfortunately I have seen first hand a course fisher on the lower Waikato , catching and releasing big koi , when approached in a friendly manner, we were told he didn’t care , so that’s 1 responsible fisher and 1 not so responsible, risk benefit analysis is not looking good for course fishing is it

      Alan Knowles 26/08/2022 at 5:49 pm

      That is so much BS. Perch scoff all fish fry including bullies which are essential for kakahi lifecycle. The fresh water mussels are the lakes’ filter system and their populations are declining becaese of pest fish like perch. Result is algal blooms and dieing lakes.


    Congratulations and well done. Such a destructive species and even only one monster would’ve degraded the quality of that habitat for native fish and invertebrates.


    Nice work, and a good tale. 🙂

    Peter Hallinan 13/07/2022 at 4:21 pm

    A poignant story, well told.