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Is DOC poisoning our fisheries?

Since October 2018 DOC is overseeing the “”control work” of eliminating colonies of the native black backed gulls on the popular fishing river beds in North Canterbury. They have the support of Environment Canterbury and the local Hurunui Zone Committee.

DOC’s website states that black-backed gulls are known to prey on the eggs and chicks of black-fronted tern/tarapirohe, black-billed gull/tarāpuka, wrybill/ngutu pare, and banded dotterel/tūturiwhatu — all endemic threatened birds that breed on the braided Hurunui river. Surely we need to ask “why” has this suddenly become a problem?

Zone Committee Chair John Faulkner said Canterbury’s braided rivers, including the Hurunui, are unique. “They support many important fish, animals and plants. The birds that depend on these rivers are declining,” he said. “That is why we are supporting this important control operation.” Note that nowhere do they consider the effects of nearby intensification of farm practices. Ploughing and/or heavy irrigation both bring earthworms to the surface and into the vision of the “early bird”, and both are acknowledged as providing greater attraction for the gulls than conventional dry land farming practices.

Faulkner reported that 77% of nests were destroyed on the Hurunui last season after being preyed on by eithermammalian or avian predators. Note that he could not specifically say “preyed on by black backed gulls”. Nor did the website say how much of the river’s 2,670 sq km catchment was surveyed.

Pest control firm “Wildlife Management International” carried out the Hurunui control work. The toxin alpha-chloralose, an anaesthetic compound registered for black-backed gull control, was mixed with margarine on bread bait and hand laid within gull colonies.  It is a narcotic which invariably leads to death. All uneaten baits and gull carcasses were to be removed for disposal within 24 hours. Warning signs were to be in place at entry points to the operational areas. Alpha-chloralose has been widely used to control birds considered a “nuisance”.

Alpha-chloralose bread baits and gull carcasses are toxic to domestic animals, as well as people, if eaten. People are advised to avoid the control areas while signs remain in place and not to take their pets into these areas. Contractors have stated that it immobilises within seconds of ingestion. A paper published about this chemical’s use in New Zealand, by the University of Nebraska, states clearly that this poison should not be used near waterways. DOC is using it on braided river beds; rivers which are prone to regular floods or “freshes”.

Without any visible notification on their website the programme has already moved south to the Rakaia catchment. A member of the public was alerted to their actions by the sound of rifle fire. It was in an area of the Rakaia Gorge accessible only by jet boats. It is a vital passage way for migrating salmon, and salmon anglers. On inspection he saw the contractors, dressed like alien Darth Vader storm troopers who were “finishing off” poisoned black backed gulls with what appeared to be 22 rifles. Other users of this “pesticide” have claimed that the birds usually “drop” within a few seconds of taking the bait and are collected up.

My informant moved off and saw uncollected gull carcasses in paddocks hundreds of metres away; ideal fodder for hawks, falcons, and other scavengers.  

Two sights on the river shocked him; dead gulls and dead eels. One eel was as thick as a man’s thigh, a real “grandmother” eel; probably 50 years old. Several more dead eels followed. At my request he returned two weeks later to photograph the eels. Unfortunately they had decayed enough to make an autopsy irrelevant. That their carcasses are lying near a dead gull is interesting.

Usually 2 + 2 = 4. Therefore dead gulls in the river + dead eels = probable connection. Photos 2 weeks later

The terns, wry-bills, black-bills and banded dotterels have co-existed with Larus dominicanus for thousands of years on our post-glacial braided rivers. L.dominicanus has many names: Black-backed gull, Dominican gull, Kelp gull and Karoro. The “Dominican” name comes from the black and white robes of Europe’s Dominican friars. It has related sub-species across the globe but the New Zealand population has filled an important environmental niche here for millions of years. If it is now out of synch with other native species then we need to look at factors such as: encroachment of farming onto river beds, changes in river bed border vegetation, water abstraction, nearby pesticide use on traditional invertebrate food sources (aquatic and terrestrial) of native bird species, and the whole variety of direct and indirect human influences, to see what can be done to remediate their effects; rather than resort to spreading yet another lethal chemical into New Zealand’s river catchments.

The logic behind “blaming” the gulls for the problem suggests that DOC and ECan find it easier to eliminate them than tackle the real root causes; agricultural practices. The dead eels may be just the start of the damage in our fisheries from DOC’s ongoing chemical warfare approach to environmental management.

Footnote: Rex N. Gibson is an ecologist with a deep personal interest in healthy rivers and outdoor recreation. He is a freshwater spokesperson for the N.Z, Federation of Freshwater Anglers.