Rainbow trout

Image: PXhere

Introduction

Studies confirm 1080 operations have no effect on trout, nymphs and fish or the water in which they live. Studies also confirm consuming 1080 directly does not harm trout.

Research in laboratories and in natural waterways has tested the effect of artificially high doses of 1080 on trout and the environment. No effects on trout or the ecology of the test area were found. The research also demonstrated that trout were safe to eat 7 days after a 1080 operation.

Fish have a different metabolism to rats, mice and possums. This is thought to be why trout are not affected by the same (or much higher) dose of the toxin received by the animal predators targeted in 1080 operations. 

Trout and 1080 pellets

Trout are not attracted to 1080 pellets and there are no direct or anecdotal reports of trout being caught with intact pellets in their guts. Trout swallow their food whole and would be unlikely to be able to swallow a fresh, hard 1080 bait.

A trial at the Tongariro National Trout Centre offered rainbow trout the cinnamon-flavoured non-toxic cereal pellets that are used as a pre-feed in 1080 operations. These rainbow trout were used to eating other kinds of artificial food (pellets fed to salmon). Several trout were seen picking up the pellets in their mouths, but all spat them out again. No pellets were eaten after an hour.

Trout and poisoned mice

Mice are one of the rodents affected by predator control operations in New Zealand, and anglers expressed concern about the effect that eating poisoned mice could have on trout. In response, we commissioned the Cawthron Institute to carry out a risk assessment.

In their 2014 laboratory study, the effect of trout eating a large number of poisoned mice was simulated by dosing with the toxin (via a capsule placed in their gut) at levels much higher than would occur in the wild. No fish died and no changes in their behaviour were observed during the research. Trout took up small amounts of 1080 in their flesh and these amounts reduced over time as the 1080 broke down.

Trout and food safety

The Cawthron research study was subsequently assessed by the Ministry for Primary Industries (MPI), which is responsible for food safety in New Zealand. MPI found that the 1080 levels in trout flesh fell well short of breaching international standards for human health. The assessment also stated that the peak 1080 levels were a 'gross over-estimate' of any 1080 residue likely to be found in wild trout.

In 2016, we asked MPI to update their risk assessment for trout eating a 1080 pellet directly, rather than from poisoned mice. (This was to test a hypothesis proposed by Fish & Game of trout eating 1080 pellets). MPI found the possibility of a small food safety risk but noted that the possibility was highly unlikely to occur in trout in the wild (because pellets are applied sparingly and 1080 washes out of pellets quickly).

Food safety advice

As a precaution, MPI advises anglers to avoid eating trout from waterways in a 1080 operation area for 7 days. You can read more about food safety on our MPI risk assessment page.

Case study: Taupo Fishery

Taupo is known internationally for its high-quality trout fishing – brown and rainbow trout thrive in near-pristine streams, rivers and lakes. Anglers from all over the world enjoy superb summer dry fly fishing or using heavy nymphs in winter to catch premium trout migrating upstream.

Lake Taupo’s spawning tributaries are healthy and hyper-productive, with the many juvenile trout growing quickly on a rich diet of nymphs and larvae. Taupo is the most studied fishery in New Zealand. With nearly 30 years of robust data and ongoing fishery research, its international reputation for high quality science is well deserved.

Ongoing predator control in the lake catchments with traps and 1080 is essential. This has enabled the number of native birds (including the rare whio/blue duck) to increase, which are seen and heard more often by fishers. In 40 years of 1080 use, no negative effects on trout, their prey or water quality have been recorded.

Nymphs and insects

1080 in water does not affect insects and their larvae such as caddisflies, mayflies and midges (collectively known as invertebrates). Five different studies from 1994–2005 all reported that 1080 had no detectable impact on aquatic invertebrates.

In one study, 1080 pellets were put into four streams to simulate what would happen after a 1080 operation. Even at the artificially high levels (10 times greater) used in this study, there was no effect on the communities of invertebrates that were 10 and 100 m downstream of the baits.

The study collected, counted and identified 87,889 individual invertebrates from 72 taxa (species) by rolling over 10 submerged rocks at each site. The number of individuals was also counted before the 1080 was added as an experimental control.

References

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