5.2 Outcomes for other native species
Bats
New Zealand has two species of bat: short-tailed and long-tailed. The short-tailed bat, which is primarily insectivorous but also eats fruit, nectar and pollen, did not eat carrot or cereal-based baits in feeding trials. The short-tailed bat feeds on ground-dwelling invertebrates, which are known to eat 1080 baits. Since bats may be vulnerable to secondary poisoning after aerial 1080 operations, it is important to determine the possible effects on short-tailed bat populations. One bat population was monitored in 1997, following an aerial operation using cereal-based baits, and showed no detectable impacts from poisoning38. More research is required to check for possible impacts, but monitoring bat populations is difficult. However, like native birds, short-tailed bats benefit from reduced possum numbers, as possums are competitors for the fruits and flowers that the bats feed on.
The long-tailed bat is entirely insectivorous, feeding in flight, mainly within or above the canopy, on flying invertebrates. This species is, therefore, only ever likely to suffer secondary 1080 poisoning, and the risk of this is considered minimal.
Frogs and lizards
Overseas studies indicate that both frogs and lizards are less sensitive to 1080 than most other groups of animals. They would need to eat large quantities of poisoned bait or poisoned insects to receive a lethal dose. New Zealand's three species of native frog have very restricted distributions and are rarely exposed to aerial 1080 operations. They are also not known to eat carrot or cereal-based baits. There was no evidence of any impact on populations of Hochstetter's frog or Archey's frog from two aerial 1080 operations that included frog habitat.
There are 17 species of native geckos and 22 species of native skinks in New Zealand, but there is little information about how many of them live in areas where aerial 1080 operations have been carried out. New Zealand lizards feed mostly on insects and theoretically might be at risk of secondary poisoning. Australian experiments strongly suggest that, given their high tolerance to 1080, lizards would not be able use to consume enough 1080 in poisoned insects or other animals to receive a lethal dose. Lizards have not been monitored after aerial 1080 operations, although this would be advisable.
"Mainland Islands" - Testing the arguments
Whether "silent forests are caused by pests" or "silent forests are caused by 1080" is an argument that needs to be evaluated, based on good evidence, in discussions on the use of 1080 in New Zealand.
Freshwater animals
Aerial operations avoid dropping baits near major waterways, with the result that monitored 1080 levels in waterways are zero or at trace levels only (see Chapter 5.5). The breakdown and solubility properties of 1080 also mean that any presence is transient, and the rare traces that do occur disappear in a few days. Given the low sensitivity of fish and freshwater invertebrates to 1080, the risk to freshwater species is probably negligible.
Freshwater eels
The long-finned eel, called "tuna" by Maori, is a taonga species for many iwi and is unique to New Zealand's streams and rivers. Recent preliminary research by Landcare Research (Manaaki Whenua) examined the possible effects of 1080 on long-finned eels, including the risks to humans if eels had eaten poisoned possum tissue, in the unlikely event dead possums got into waterways. There was no evidence that eels would eat 1080 cereal baits that are added to water, nor was any 1080 detected in eel tissue from water contaminated by baits.
Captive eels were presented with "sausages" filled with poisoned possum tissue of either minced muscle or gut tissue. The tissue in the "muscle sausage" contained about 1400 parts per billion (ppb) of 1080; the "gut sausage" contained about 8300 ppb of 1080. Eels ate both types of sausages, but none later died. The amount of 1080 in the eels dropped over time, but low levels were still detected 11 days after eels had fed on poisoned possum tissue. The highest 1080 concentration remaining in an eel from a "gut sausage" was measured at about 38 ppb after 3 days. A 60-kg person would need to eat about 5.5 tonnes of eel flesh at this concentration to risk death, based on an estimated LD50 for humans of 3.5 mg/kg body weight (see Chapter 3, "Comparison of species sensitivity" for explanation of LD50 values). These are all preliminary research findings only and are still subject to assessment by the Animal Health Board's peer review protocol.
Invertebrates
The seven most common groups of ground-dwelling invertebrates that have been seen feeding on carrot and cereal-based baits are ants, beetles, springtails, amphipods, harvestmen, mites and weta. The impact of aerial 1080 operations on invertebrate populations has been monitored by four pitfall trapping studies and two direct counting studies. Three of the four pitfall trap studies showed no effects on ground-dwelling invertebrates, up to 6 or 12 months after cereal-based and carrot bait aerial 1080 operations40. The fourth study showed short-term reductions in the numbers of ground-dwelling invertebrates. However, there were 10 times the normal number of baits within one metre of the pitfall traps in this study, which was highly likely to have affected the results. This study was eventually repeated with normal bait densities and no differences were detected in invertebrate levels between the treatment and control areas.
In one of the two studies that counted invertebrates feeding after aerial 1080 operations, numbers declined within 20cm of the baits, but recovered within three days after removing the baits. These studies suggest that it is only invertebrates living within a short distance (about 20cm) of a poison bait that are potentially at risk. As the number of baits dropped per hectare has decreased significantly, so too has the potential exposure of invertebrates to toxic baits. Neither of these studies suggested there would be long-term negative effects on ground-dwelling invertebrate populations, which is also the conclusion from the scientifically-robust pitfall trapping studies.
Possible impacts on tree weta and cave weta have also been studied by monitoring the occupancy of artificial nests before and after 1080 application. There was no change in nest occupancy following 1080 bait application around the nests41.
Although invertebrates get less public attention than native birds, they play vital roles in all ecosystems. The scientific evidence to date is that insect populations are not adversely affected by aerial 1080 operations. On the contrary, possums, along with rodents, are major predators of native invertebrates (see Chapger 3.4) and low possum numbers benefit many insect and other invertebrate species.
In summary:
"Despite the loss of some individuals, there is no evidence of deleterious long-term impacts of 1080 poisoning for possum control on populations of any non-target species that have been adequately monitored. Mortality from poisoning either is occurring in place of mortality from other causes such as predation or winter starvation, or is compensated for by increased breeding success of survivors."33
Possum control in Egmont National Park
DOC has relied heavily on aerial application of 1080 to achieve control of possums in Egmont National Park, for the protection of the forests and wildlife of the park.
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