Non-target Species

The potential impacts to non target species and the environment arising from the proposed REP were extensively assessed through the various environmental approval documents and processes.

These included:

  • Pollution of soil, air or water
  • Bioaccumulation
  • Mortality of non-target species due to primary poisoning from consumption of bait pellets
  • Mortality of non-target species due to secondary poisoning from consumption of poisoned rodents, fish or invertebrates
  • Bird strikes and collisions from helicopter activity
  • Disturbance from helicopter activity
  • Potential impacts as a result of handling and captive management during the captive management program
  • Long term changes to ecological relationships affecting threatened species following the eradication of rats, mice and owls.

Based on evidence from similar eradications around the world, studies done on LHI, the physical and chemical properties of the bait and toxin and the relatively small quantity used in a one-off eradication, the risk to the environment and most species from the REP was shown to be very low.

The only species considered to be at significant risk from the REP were the LHI Woodhen and LHI Currawong. Mitigation is in place to manage risks to these two species through a detailed plan to manage large proportions of the populations of these two species in captivity during the REP. The captive management component of the REP will be managed by animal husbandry experts from Taronga Zoo including vets, vet nurses and experts in bird management. Both species have previously been held in captivity before with no observable ill effects (read more). With the captive management in place, it is considered unlikely that the REP will have a significant impact on woodhens or currawongs.

Reports – Trial research

Non-toxic bait trial

Captive management trial

Rodent bait uptake trial

Carlile and Wheeler efficacy trials

Efficacy of Pestoff 20R on LHI mice

Fish study final report

An extensive monitoring program will be conducted before, during and after the REP.

This includes:

  • Monitoring of weather in the lead up to and during the REP. This will ensure bait can be distributed safely and effectively and not during adverse weather conditions.
  • Monitoring for non-target species deaths after bait distribution to ensure there are no unexpected impacts to endemic species.
  • Monitoring breakdown of baits after distribution. This will provide confidence in bait breakdown prior to release of captive managed species.
  • Soil monitoring before and after bait distribution. This will provide evidence that pollution has not occurred.
  • Random sampling will be conducted on water bodies on the island to monitor Brodifacoum levels before and after the bait drop. This will provide evidence that pollution has not occurred and water is safe to drink.
  • Monitoring of Woodhen post release. This will provide evidence of recovery.
  • Monitoring of free-ranging currawong and captive Currawong LHPC post-release. This will provide evidence of impacts and recovery.

 Potential Environmental Benefits from proceeding with the REP

The many successful rodent eradication programs undertaken on islands around the world have shown that the benefits to native plants and animals are both significant and immediate (Jones et al, 2016)[1].

Benefits include:

  • significant increases of seeds and seedlings of numerous plant species on islands after the eradication of various rodent species
  • rapid increases in the number of ground lizards (e.g. geckos, skinks) following removal of rats – including a 30-fold increase in one case
  • dramatic increases in the numbers of breeding seabirds and fledging success
  • rapid increases in forest birds and invertebrates.

The anticipated benefits specifically relating to the REP on the LHIG include:

  • recovery of a range of species an ecological communities directly at risk of extinction due to rodents such as the cloud forest snail species, LHI Placostylus, Little Mountain Palm, Phillip Island Wheat Grass and Gnarled Mossy Cloud Forest
  • a marked increase in birds, reptiles and insect density, diversity and distribution – this boost in diversity will increase food resources for predatory terrestrial vertebrates and potentially lead to population increases which will enrich the experience of both island residents and tourists
  • increases in the abundance of plants, seeds and seedlings, thereby enhancing the process of forest regeneration
  • removal of the economic and environmental burden of the ongoing control currently in place, eliminating the need for the ongoing use of rodent poisons in the environment and their associated long-term risks to native species, pets, livestock and people
  • the ability to return species (or closely related surrogates/ecological equivalents) that have long been absent due to the predation of rats and mice, such as the Island gerygone, grey fantail, Boobook Owl, LHI Wood-feeding Cockroach and LHI phasmid
  • Long term positive impacts for tourism through protection and enhancement of World Heritage values and improved visitor experience of a rodent free World Heritage Area.

There is a clear and demonstrated need for the REP based on documented evidence of significant impacts of rodents both globally and on LHI at the species and ecosystem level, even in the presence of ongoing rodent control. There are unacceptable consequences of failing to proceed with the REP.

The REP is essential and beneficial. Risks have been addressed through proposed mitigation to the point where they are considered to be very low. Any potential impacts are localised and short term and far exceeded by the benefits that will be provided by implementation of the REP. Potential impacts of the REP are also considerably less than the ongoing impact of failing to proceed.

[1] Jones H. P., Holmes N. D., Butchart S. H., Tershy B. R., Kappes P. J., Corkery I., Aguirre-Monoz A., Armstrong D. P., Bonnaud E., Burbidge A. A., Campbell K., Courchamp F., Cowan P. E., Cuthbert R. J., Ebbert S., Genovesi P., Howald G. R., Keitt B. S., Kress S. W., Miskelly C. M., Oppel S., Poncet S., Rauzon M. J., Rocamora G., Russell J. C., Samaniego-Herrera A., Seddon P. J., Spatz D. R., Towns D. R. and Croll D. A. (2016) Invasive mammal eradication on islands results in substantial conservation gains. PNAS 113, 4033-8

[2] DEWHA, (2009). THREAT ABATEMENT PLAN to reduce the impacts of exotic rodents on biodiversity on Australian offshore islands of less than 100 000 hectares. Department of Environment Water, Heritage and the Arts, Canberra