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Methods for monitoring invertebrate response to vertebrate eradication

Island and Ocean Ecosystems, BRB

Available Online

Houghton, M.

Shaw, J.

Terauds, A.

Once an island vertebrate eradication is deemed successful, it is typically assumed that ecosystem recovery will follow. To date, most post-eradication monitoring focuses on the recovery of key threatened or charismatic species, such as seabirds. Little attention has been given to monitoring and quantifying the response of invertebrate communities. Rabbits (Oryctolagus cuniculus), house mice (Mus musculus), and ship rats (Rattus rattus) impacted sub-Antarctic Macquarie Island for over 140 years, with wide ranging ecosystem impacts. In 2014, the eradication of rabbits and rodents was o?cially declared successful. To determine whether management objectives are being met, we are investigating the response of invertebrate communities to pest eradication, using both historic data and contemporary surveys to track changes over space and time. To achieve this, we have developed a survey strategy that is e?ective and e?cient. Here we report on the merits of utilising a variety of invertebrate trapping methodologies to establish current baselines for future invertebrate monitoring. We identify sampling techniques that are most e?ective for speci?c groups of taxa, particularly those of interest to post-eradication monitoring, and how the implementation of such methods can improve and facilitate e?ective post-eradication monitoring of invertebrates.

The Rangitoto and Motutapu pest eradication - a feasibility study.

Available Online

Griffiths, Richard.

Towns, David.

The eradication of the seven remaining animal pest species remaining on Rangitoto and Motutapu was announced by the Prime Minister and Minister of Conservation in June 2006. With stoats, cats, hedgehogs, rabbits, mice and two species of rats spread across an area of 3842ha, the proposed project is the most challenging and complex island pest eradication the Department of Conservation (DOC) has ever attempted. To better understand the scale and complexity of the project, a feasibility study was undertaken. This study considered the ecological, economic and social context of the project to allow an informed decision to be made on whether or not to commit resources to further eradication planning. This document outlines the findings of the feasibility study and concludes that while a number of contingencies exist within the project, the proposed eradication is not only feasible, but has many significant benefits. No single precedent exists on which this project can be modelled and information from a wide range of sources has been required. Previous eradication and control programmes have been reviewed in conjunction with what is known about the behaviour and biology of the target species. In some cases, where information has not been available and could not be inferred, trials have been undertaken. The document has been reviewed by a number of experts both within New Zealand and overseas including DOCs Island Eradication Advisory Group. Consultation has also been undertaken with all of the islands key stakeholders and communities of interest. Comments from all of these parties have been reflected in the report. Rangitoto is an iconic Scenic Reserve located just 9km from downtown Auckland City. The island is internationally significant both for its ecology and geology and is an extremely popular visitor destination served by regular ferry services. Motutapu, a Recreation Reserve, is connected to and positioned immediately to the east of Rangitoto. The island, currently managed as a pastoral farm, is noted for its extensive archaeological record but retains a diverse range of habitat types and is the focus of a community-led restoration programme. In addressing the question, can it be done? particular attention has been paid to mice, ship rats, hedgehogs and rabbits as eradication of these species on the scale of Rangitoto and Motutapu has never been attempted. Preventing reinvasion on such highly accessible and intensively visited islands is also an enormous undertaking. It is accepted, that of all the target species, mice present the greatest risk of failure. However, while a number of mouse eradications around the world have failed, all ten attempts on islands beyond the swimming range of mice that have followed current Departmental best practice have been successful, providing confidence in the method. Rangitoto and Motutapu are a significant step up from previous operations in terms of scale but are also the logical next step to apply current techniques. Despite the unprecedented elements within the project, it is considered that the key dependencies on which eradication success relies can be met for the species targeted. Preventing reinvasion is perhaps the most important consideration of the feasibility study and the one that will ultimately determine the fate of the project. Achieving an adequate level of protection for the islands hinges heavily on changing the behaviour of all 100,000 visitors that arrive on an annual basis. Without this any investments made in removing pests will be wasted. Bringing these changes about appears possible but is contingent on a number of commitments and actions that must be put in place by both DOC and its key partners. The feasibility study also addresses what the project will take to complete and attempts to identify as many of the planning issues as possible to enable the project to be properly sized. It explores the techniques that must be used, the resources that will be required and the timeframe over which they need to be deployed. While this eradication project is the most challenging and complex to be undertaken by DOC, it also presents a significant opportunity to improve our current understanding of eradication theory and practice. If successful, the project offers outstanding benefits for conservation. The recovery of locally and nationally endangered species, the creation of a stepping stone for wildlife movement between the Hauraki Gulf and the Auckland isthmus, the potential for advocacy and education, and increased recreation and economic opportunities are just some of the likely gains. The study has shown that this project is feasible, but also that there are many significant reasons why it should proceed.

Potential economic damage from introduction of Brown Tree Snakes, Boiga Irregularis (Reptilia: Colubridae), to the Islands of Hawaii

Gebhardt, Karen

Kirkpatrick, Katy N.

Shwiff, Stephanie A.

Shwiff, Steven S.

The Brown Tree Snake (Boiga irregularis) has caused ecological and economic damage to Guam, and the snake has the potential to colonize other islands in the Paci c Ocean. This study quanti es the potential economic damage if the snake were translocated, established in the state of Hawaii, and causing damage at levels similar to those on Guam. Damages modeled included costs of medical treatments due to snakebites, snake-caused power outages, and decreased tourism resulting from effects of the snake. Damage caused by presence of the Brown Tree Snake on Guam was used as a guide to estimate potential economic damage to Hawaii from both medical- and power outagerelated damage. To predict tourism impact, a survey was administered to Hawaiian tourists that identi ed tourist responses to potential effects of the Brown Tree Snake. These results were then used in an input-output model to predict damage to the state economy. Summing these damages resulted in an estimated total potential annual damage to Hawaii of between $593 million and $2.14 billion. This economic analysis provides a range of potential damages that policy makers can use in evaluation of future prevention and control programs.

Rat eradication on small islands in the Vava'u group, Kindom on Tonga

Available Online

Houston D.M.

In June/July 2002 the eradication of Pacific rats from Maninita Island in the Vava'u group of the Kingdom of Tonga was attempted using Brodifacoum pellets in bait stations. In December 2002, Maninita was revisited and rat trapping carried out to determine if rats were present. While no rats were caught and none were seen, further monitoring in June 2003 is recommended before the island is declared "rat free '. Using the same techniques used on Maninita, the eradication of rats on neighbouring Taula and Lua Loli was attempted. Despite poor weather delaying rebaiting visits to the islands, the operation thus far appears successful. Permanent bait stations set up on Maninita to minimise the risk of rats re-invading the island were found to have been tampered with and evidence of booby chick harvesting was seen on Taula. Regular visits to the islands to maintain bait stations and maintain a presence are recommended.

Conservation of the Tahiti flycatcher (Pomarea nigra) : Report on advice provided to Societe d'Ornithologie de Polynesie

Island and Ocean Ecosystems, BRB

Available Online

Blanvillian, C.

Pierce, R.J.

The Tahiti flycatcher (Pomarea nigra) is one of several monarch flycatcher species in the Polynesian genus Pomarea, all of which are threatened. The Tahiti flycatcher is currently known from only the western side of Tahiti where, during the 1998-99 season, at least 24 individuals, including 10 pairs, were located in four valleys (Blanvillain 1999). Although ten nests were protected from rats in 1998-99, only three were successful in fledging young. Two of these young apparently disappeared one week after fledging and the third, two months after fledging (Blanvillain 1999). Concern was raised about the possible predation by common myna (Acridotheres tristis), and/or red-vented bulbul (Pycnonotus cafer) on juveniles. In 1999-2000 the Societe d'Ornithologie de Polynesie (MANU) was granted funding for Tahiti flycatcher conservation by the South Pacific Regional Environment Programme (SPREP). During 13-26 September 1999, RP visited Tahiti to advise and help CB with aspects of the programme. This advisory work was funded by the N.Z. Ornithological Congress Trust Board (ICBP). It builds on work by Gaze & Blanvillain (1998) funded by the Pacific Development and Conservation Trust.

Environmental effects of rodent Talon baiting Part I : Monitoring for toxic residues : Part II Impacts on invertebrate populations

Available Online

Morgan, D. R.

Spurr, E. B.

Wright, G. R.

Although Talon® baits containing brodifacoum have been used successfully in eradicating rats from some of New Zealands offshore islands, little is known about any environmental effects of this toxin. We sampled invertebrates, blackbirds, soil, and water at intervals of 2 days to 9 months to determine whether brodifacoum residues were present after aerial distribution of Talon® 20P cereal pellets on Red Mercury Island and after bait-station use of Talon® 50WB wax-coated cereal blocks on Coppermine Island. No brodifacoum residues were found in soil, water, or most (99%) invertebrate samples. Low to moderate residues were found in one sample of slugs collected 2 days after aerial sowing. Tissues from all birds (n=4) and rats (n=3) found dead and livers from all six birds collected alive 8 months after aerial baiting also contained low to moderate residues. These preliminary results suggest that few invertebrates are likely to be contaminated as a result of Talon® baiting. Tentatively, we suggest that although some invertebrates may eat Talon® baits, it appears that the brodifacoum is either metabolised and/or excreted within a few days. The dead blackbirds found, therefore, were more likely to have been killed by primary than by secondary poisoning. Further monitoring for brodifacoum residues after Talon® operations should be undertaken to confirm that contamination of invertebrates, soil, and water is unlikely. Some bird species may be at risk from Talon® baiting. Likely effects on population levels of such species should be considered to help assess the risk and benefits of Talon® use in rodent eradication.

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