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Rat eradication comes within a whisker! A case study of a failed project from the South Pacific

Island and Ocean Ecosystems, BRB

Available Online

Amos. W

Brooke. M. de L

Churchyard. T

Nichols. H.J

To enhance their conservation value, several hundred islands worldwide have been cleared of invasive alien rats, Rattus spp. One of the largest projects yet undertaken was on 43 km2 Henderson Island in the Pitcairn group, South Pacific, in August 2011. Following massive immediate mortality, a single R. exulans was observed in March 2012 and, subsequently, rat numbers have recovered. The survivors show no sign of resistance to the toxicant used, brodifacoum. Using pre and post-operation rat tissue samples from Henderson, plus samples from around the Pacific, we exclude re-introduction as the source of continued rat presence. Microsatellite analysis of 18 loci enabled comparison of genetic diversity of Henderson rats before and after the bait drop. The fall in diversity measured by allele frequency change indicated that the bottleneck through which the breeding population passed was probably around 50 individuals, representing a census population of about 60-80 animals. This is the first failed project that has estimated how close it was to success.

Eradication of common mynasAcridotheres tristisfrom Denis Island, Seychelles

Available Online

Feare, Chris J

van der Woude, Jildou

In Seychelles, the common myna has been shown to have a negative impact on endangered endemic birds on Denis Island, interfering with breeding attempts and attacking adult endemic birds at their nests. This stimulated an attempt to eradicate the island's mynas.

Special Issue Article: Tropical rat eradicationNon-target species mortality and the measurement of brodifacoum rodenticide residues after a rat (Rattus rattus) eradication on Palmyra Atoll, tropical Pacific. Biological Conservation. Volume 185, May 2015

Island and Ocean Ecosystems, BRB

Available Online

Berentsen. A.R

Eisemann. J.D

Howaldd. G .R.

Pitt. W.C

Shiels. A.B

Volker. S.F

Wegmann. A.S

The use of rodenticides to control or eradicate invasive rats (Rattus spp.) for conservation purposes has rapidly grown in the past decades, especially on islands. The non-target consequences and the fate of toxicant residue from such rodent eradication operations have not been well explored. In a cooperative effort, we monitored the application of a rodenticide, Brodifacoum 25W: Conservation, during an attempt to eradicate Rattus rattus from Palmyra Atoll. In 2011, Brodifacoum 25W: Conservation was aerially broadcasted twice over the entire atoll (2.5 km2) at rates of 80 kg/ha and 75 kg/ha and a supplemental hand broadcast application (71.6 kg/ha) occurred three weeks after the second aerial application over a 10 ha area. We documented brodifacoum residues in soil, water, and biota, and documented mortality of non-target organisms. Some bait (1419% of the target application rate) entered the marine environment to distances 7 m from the shore. After the application commenced, carcasses of 84 animals representing 15 species of birds, fish, reptiles and invertebrates were collected opportunistically as potential non-target mortalities. In addition, fish, reptiles, and invertebrates were systematically collected for residue analysis. Brodifacoum residues were detected in most (84.3%) of the animal samples analyzed. Although detection of residues in samples was anticipated, the extent and concentrations in many parts of the food web were greater than expected. Risk assessments should carefully consider application rates and entire food webs prior to operations using rodenticides.

Special Issue Article: Tropical rat eradicationBest practice guidelines for rat eradication on tropical islands. Biological Conservation. Volume 185, May 2015

Island and Ocean Ecosystems, BRB

Available Online

Boudjelas. S

Broome. K

Cranwell. S

Griffiths. R

Keitt. B

Millett. J

Pitt. W

Samaniego-Herrera. A.

Invasive vertebrates are a leading cause of the extinction on islands and rats (Rattus spp.) are one of the most damaging to island ecosystems. Methods to eradicate rates from islands are well established and there have been over 580 successful eradications to date. Increasingly, rat eradications are being implemented on tropical islands, a reflection of the need to protect the threatened biodiversity in the tropics. Yet rat eradications on tropical islands fail more frequently than those in temperate climates. In an effort to identify the main reasons for the lower success rate on tropical islands and possible solutions, a workshop was convened with the 34 experts in rat eradication, tropical rodent and island ecology and toxicology. The workshop focused on projects using aerial broadcast of brodifacoum, a 2nd generation anticoagulant, because this approach had provided the highest success rate for eradicating rodents from islands. The workshop participants reviewed previously identified challenges to successful rat eradications on tropical islands including increased insect and crab densities resulting in competition for bait, year round or unpredictable timing of breeding rats and increased or unpredictable availability of alternative, natural foods. They also identified a number of new, likely reasons for the lower success rate on tropical islands and provided recommendations for how to address these risks in the planning and implementation of rat eradications. While the success rate of aerial broadcast rat eradications in tropical environments is quite high at 89%, it is hoped that by following the recommended best practices provided in this paper, future success rates will be closer to the 96.5% demonstrated for aerial broadcast rat eradication on temperate islands.

Special Issue Article: Tropical rat eradicationFactors associated with rodent eradication failure. Biological Conservation. Volume 185, May 2015

Island and Ocean Ecosystems, BRB

Available Online

Alifano. A

Griffiths.R

Holmes. N.D

Pott. M

Russell. J.C.

Wegmann. A.S

Will.D

Invasive rodents have an overwhelmingly detrimental impact to native flora and fauna on islands. Rodent eradications from islands have led to valuable biodiversity conservation outcomes. Tropical islands present an additional suite of challenges for rat eradications due to unique characteristics associated with these environments. To date tropical island rat eradications have failed at a higher rate than those undertaken outside the tropics. Critical knowledge gaps exist in our understanding of what drives this outcome. We collated an in-depth dataset of 216 rodenticide based rat eradication operations (33% of all known rodent eradications) in order to determine correlates of eradication failure, including both project implementation factors and target island ecology, geography and climate. We assessed both failed and successful projects, and projects inside and outside the tropics, using random forests, a statistical approach which compensates for high dimensionality within, and correlation among, predictor variables. When assessing all projects, increasing mean annual temperature, particularly above 24 °C, underscored the higher failure rate and greater difficulty of rodent eradications on islands in lower latitudes. We also found clear trends in eradication failure for factors unique to the tropics, including the presence of land crabs burrowing and hermit crabs, and coconut palms (Cocos nucifera). The presence of agriculture was also associated with failure. Aerial operations had a higher success rate than ground-based methods but success with this technique was less likely in the presence of hermit crabs and other non-target bait consumers. Factors associated with failure in ground-based eradication methods suggested limitations to project scaling such as island area and number of staff. Bait station operations were less likely to succeed when using stopping rules based on measures of rodent abundance. Factors influencing rat eradication failure in tropical environments continue to require a deeper understanding of tropical island dynamics to achieve a higher rate of eradication success.

Operational Plan for the eradication of Pacific Rats (Rattus exulans) from Late Island

Available Online

Bonham, J.

Griffiths, R.

This plan sets out the operational detail, logistics and framework for a planned eradication of introduced Pacific rats from Late Island (1,731ha) in the Kingdom of Tonga. The method for the eradication is the delivery of grain-based bait containing the anticoagulant brodifacoum, into every potential rodent territory on the island. This will be done during the driest part of the year when rodents are potentially most vulnerable due to lower relative availability of natural food supplies. Because of the islands size and complex topography, the bait will be applied aerially using a helicopter with an underslung bait spreading bucket. Aerial application has been successful in eradicating rodents from many islands around the world, and the logistics and methodology are based upon similar successful operations. Mitigation measures will be required for key non-target species, especially the Friendly-ground dove. Monitoring of rodents and native species before and after the operation will be required to assess the success and effect of the operation.

Operational Plan Toloa Rainforest Restoration Project 2014-2020

Climate Change Resilience, BRB

Available Online

James Atherton

The Operational Plan for the Toloa Rainforest Restoration Project was prepared for the Ministry of Environment, Energy, Climate Change, Disaster Management, Meteorology, Information and Communication (MECCDMMIC), Tupou College and other partners under the Global Environment Facility Pacific Alliance for Sustainability (GEF-PAS) funded Prevention, control and management of invasive alien species in the Pacific Islands project.

Managing the impacts of the little fire ant (Wasmannia auropunctata) in French Polynesia (full report) = Gestion des impacts de la petite fourmi de feu (Wasmannia auropunctata) en Polynesie francaise

SPREP Publications, Island and Ocean Ecosystems, BRB

Available Online

SPREP

The little fire ant, Wasmannia auropunctata, is a small ant native to Central and South America which has been introduced into seven Pacific Island groups. It is considered by invasive experts to be the greatest ant species threat within the Pacific Region. Although its official discovery in Tahiti was in 2004, it is likely that the little fire ant has been present in Tahiti for much longer. The centre of contamination in Tahiti is the northern Mahina Commune. Initial treatment and monitoring initiatives to combat the ant invasion were carried out between 2005 and 2009, but were discontinued in 2010.

Island Invasives: Eradication and Management. Proceedings of the Conference on Island Invasives.

Available Online

Cloud, M. N. (ed.)

Towns, D. R. (ed.)

Veitch, C. R. (ed.)

The papers and abstracts published in this book are the outcome of the conference on Island Invasives: Eradication and Management held at Tamaki Campus, University of Auckland, New Zealand from 5 to 12 February 2010, hosted by the Centre for Biodiversity and Biosecurity (University of Auckland and Landcare Research), in collaboration with the IUCN/SSC Invasive Species Specialist Group. This conference had "islands" and "eradication of invasive species" as the focus, with emphasis on the work done and results or learning achieved. The conference endeavoured to cover the full breadth of this work by breaking the subject down to: Gaining political, community, financial, and physical support; Eradication techniques tested and used; The immediate results of eradication operations; The longer-term outcomes as seen in the biota of the island and among communities involved; Biosecurity measure for such islands from planning to implementation.

Restoration of Nu'utele and Nu'ulua Islands (Aleipata group), Samoa, through the management of introduced rats and ants

Available Online

Tye, A. & Butler, D. J.

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