Hundreds of native mudfish have died needlessly and we should all mourn them

Imagine if we treated our native birds with as little care as we do our precious fish stocks, writes ecologist Stella McQueen.

Earlier this year, 900 at-risk native mudfish were relocated to make way for a wastewater development. But despite a huge amount of planning, volunteer hours, and a $160,000 bill, only a handful survived. This is just the latest example of haphazard and poorly planned fish ‘rescues’ which are happening at construction and development sites all over New Zealand.

In this case, the mudfish were living in drains on the site of a new wastewater treatment plant being built near Carterton. Their habitat would have been destroyed by earthworks and the fish would not survive. So they were moved, as often happens now when streams are culverted, redirected, bridged or piped.

The problem is, brown mudfish are quite particular about the types of habitat they prefer. Their ideal home is shallow water with lots of different types of plants, such as manuka, ferns, and coprosma. These provide good shade and hiding places, as well as the occasional feed of insects that fall into the water. After wetland is drained, they may survive in the drains with shallow water, overhanging grasses and no other fish to eat them.

Where you won’t find them is in open boggy paddocks. But this is exactly where the 900 mudfish ended up. Restoration is planned for the site, but somehow the mudfish were expected to persist there for several years until the plants became established. Sadly, they didn’t survive the wait.

A large NZ native mudfish (supplied)

Imagine if native birds were relocated to a bare paddock that developers promise would be planted up with native forest in a few years’ time. Such a proposal would be laughed out of the permit office. It’s the story of moving native snails off a proposed mine site and into ice-cream containers in cool storage, all over again. Yet this is happening to threatened native fish all over the country.

It is fantastic that fish rescues are now a common condition of resource consents where waterways are adversely impacted. The plans for these relocations look great on paper, however, there isn’t enough thought going into fish welfare or releasing them into places that are suitable. On top of this, ecologists often aren’t given enough time to safely remove the fish before construction begins, or another contractor has already come through and felled trees into the stream, making fish rescue impossible.

What’s more, release sites are rarely monitored to see if the fish survived. Rescues are considered successful simply because the fish were moved out of harm’s way. Their chances of survival in their new home seems to be of little concern.

Rescuing native fish is great, but only if they are released into suitable habitat. (photo supplied)

As a native fish expert and ecologist who has worked on fish relocations throughout New Zealand, I have seen this kind of thing happen again and again.

In two cases, thousands of fish were moved from several kilometres of stream into much smaller and shorter ones. There were no resident fish thanks to down-stream barriers, which meant there was plenty of vacant space. But the new streams lacked enough habitat for the fish to hide, feed, and spawn. Again, restoration was planned in a few years’ time, but it would take years for the plants to grow. What were the fish to do until then? We will never know as monitoring is rarely required by the consent. Even if it was, there are no consequences for failure.

On another project, a developer started digging up a drain they chose not to survey prior to construction. When a thriving population of brown mudfish was discovered, ecologists moved the fish downstream to a more degraded location that would not provide long-term habitat. Because the fish were not known about in advance, nor written into the ecological plan, it was impossible to compel the developers to do anything better for them. Sadly, this is one of many times I have seen reactionary fish relocations being done at the last minute and leading to poor outcomes for at-risk species.

In some cases, basic ecology isn’t taken into consideration. I have heard of several hundred kōura (freshwater crayfish) being moved into a pond with an established kōura population. Since the pond was already at carrying capacity, this would have started a cannibalistic frenzy. Numbers would eventually stabilise back to pre-relocation levels.

A native kōura (freshwater crayfish). (Photo supplied)

The haphazard nature of these relocations needs to stop. New Zealand’s native freshwater fish are in serious trouble – 72% are classified as at-risk or threatened with extinction. Most of the decline is due to the degradation and loss of habitat. Every new culvert, piped stream, filled-in ditch, drained wetland and channelled waterway increases the pressure on these fish.

Join us and help us hire new
political & climate reporters
Find Out More

Fish rescues and relocations are included as part of the consent conditions that a developer must meet. They count as legal mitigation for the damage done to the environment. The numbers of fish moved must be carefully logged and sent to MPI as a requirement of the relocation permit. The developer gets a nice green tick and a good news story. Yet too often the fish are left to languish in inappropriate places, forgotten.

Consent and relocation plans are far too rigid. They cannot flex to accommodate unexpected discoveries. The digger is starting tomorrow therefore the fish must be moved today. Even a small change of method for fish welfare purposes is impossible once the plan has been approved.

Little research has gone into the success of fish relocations. Most has been under ideal conditions, moving single species to carefully selected, appropriate habitats. Nothing is known about the effects of releasing whole communities of fish into streams that already have their own fish. Fish relocations are being so poorly done that it could be ecologically more meaningful to ignore the affected fish and spend the money entirely on improving stream habitat elsewhere.

It’s time to stop spending thousands of dollars to move fish from the frying pan and into the fire, and to acknowledge that if they aren’t getting a ‘forever home’, it’s not mitigation. We wouldn’t put up with this treatment of native birds, and we can’t let this continue to happen to our equally unique native fish.


The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.


The Spinoff is made possible by the generous support of the following organisations.
Please help us by supporting them.