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Invasive alien species are one of the primary threats to native biodiversity on islands worldwide, and their expansion continues due to global trade and travel. Preventing the arrival and establishment of highly successful invasive species through rigorous biosecurity is known to be more economic than the removal of these species once they have established. However, many islands around the world lack biosecurity regulations or practical measures and establishing biosecurity will require social and financial investments. Guiding these investments towards islands where native biodiversity is at highest risk from potential invasions is of strategic importance to maximise conservation benefit with limited resources. Here we implement an established prioritisation approach, previously used to identify which islands will have the greatest conservation gains from the eradication of invasive species, to identify which islands would benefit the most from establishing or improving biosecurity. We demonstrate this approach for 318 islands in the Caribbean UK Overseas Territories and Bermuda where we considered all threatened native terrestrial vertebrates that are vulnerable to the most harmful invasive vertebrates (black and brown rats, cats, small Indian mongoose, green iguana). The approach calculates the increase in conservation threat score resulting from anticipated negative effects of potential invaders on native biodiversity, and highlighted Sombrero (Anguilla) and Cayman Brac (Cayman Islands) as important islands where threatened reptile species would likely be eliminated if rats, feral cats or mongoose invaded. Feasibility and cost implications should now be investigated more closely on the highlighted islands. The prioritisation presented here can be expanded to more islands and more invasive/native taxa (herbivores, plants and invertebrates), but requires a classification of the severity of potential impacts between invasive and native species for which currently little information exists. Besides highlighting opportunities for biosecurity, this approach also highlights where knowledge gaps about population sizes of and threats to reptiles with restricted ranges exist.

Montecristo and Pianosa islands, although approximately equal in surface area (c. 1,000 ha), di?er greatly in substrate, human presence, vegetation and altitude (650 m vs. 30 m asl, respectively). The former island hosts one of the largest yelkouan shearwater (Pu?nus yelkouan) populations in Italy, the latter a depleted remnant of once numerous Scopoli’s shearwaters (Calonectris diomedea). Two consecutive EU-funded LIFE projects have been designed to protect these seabird populations. On Montecristo, rough and inaccessible, aerial delivery of toxic baits in January-February 2012 eradicated black rats (Rattus rattus) and feral rabbits (Oryctolagus cuniculus) (originally a non-target species), with no permanent consequences on a local, ancient population of wild goats (Capra hircus). Eradication on Pianosa, currently underway (started January 2017), is being performed by ground baiting, delivered by 4,750 dispensers placed on a 50 m × 50 m grid throughout the island. The latter operation is included in a multi-species eradication aimed at several other target species, among which was the brown hare (Lepus europaeus), apparently introduced around 1840. Genetic analyses on the ?rst trapped hares showed that this was the last uncontaminated and viable population of L. europaeus subsp. meridiei in existence. Whether of natural origin or introduced, the commencement of eradication of this population has instead created the awareness of a taxon otherwise unavailable for conservation elsewhere. While both projects address the same conservation issues (protection of shearwater colonies and restoration of natural communities), they di?er greatly regarding economic cost, public perception, e? ort needed to maintain results in the long term and e?ects on non-target species. In the present paper, speci?c attention has been paid to the comparison between bait delivering techniques, results obtained, the array of problems originating from the complex regulatory framework and reactions by the general public.

The Orkney Islands, o? the north-east coast of Scotland, support highly significant?cant cultural and natural heritage. The combined land area of the 70 islands is 990 km2 (380 sq mi), 1% of the UK, but they host over 20% of the UK’s breeding hen harriers (Circus cyaneus) (declining over much of its mainland range), 8% of breeding curlews (Numenius arquata) (one of only two UK populations not in decline) and an internationally important assemblage of breeding seabirds. The Orkney Islands are naturally free of mammalian predators, and all bird species, including raptors, are ground-nesting in the largely treeless landscape. Rats (Rattus spp.), hedgehogs (Erinaceus europaeus) and feral cats (Felis catus) are present across the archipelago. Stoats (Mustela erminea) are native to mainland UK but not Orkney, yet were detected on Orkney Mainland in 2010. Orkney Mainland has an area of 523 km2 (202 sq mi). Early attempts at removing them were not successful. By 2013 stoats were present across the Orkney Mainland and connected isles. In 2016, SNH and RSPB formed a partnership to eradicate stoats to protect the native wildlife and designated sites of the Orkney islands, and to secure the wider socio-economic and cultural bene?ts of thriving native wildlife. Di?culties faced in developing the project include predicting the e? ort required to remove stoats at a rate faster than they can reproduce, securing community support and access to private land and, in particular, funding large scale biodiversity restoration projects. A feasibility study determined that stoat eradication would be possible using DOC200 kill traps, and search dogs in later stages of the eradication. There are no legally available poisons that could be used on stoats in the UK. A Biosecurity Plan has been produced for the archipelago, with a current focus on preventing the spread of stoats to the uninvaded isles. The partnership is working to secure funds and community support for what will be the world’s largest stoat eradication attempted to date. We present the ?ndings of the feasibility study and our proposed methodology.

A successful ground-based eradication of black rats (Rattus rattus) was undertaken on the remote, uninhabited Shiant Isles of north-west Scotland over winter (14 October–28 March) 2015–16. The rat eradication was carried out as part of the Shiants Seabird Recovery Project, which aims to secure long-term breeding habitat for protected seabirds and to attract European storm petrels and Manx shearwaters to nest on the Shiants. Throughout the eradication operation, teams were stationed on two of the three main Shiant islands (Eilean an Tighe, Eilean Mhuire), with access to the third (Garbh Eilean) via a boulder causeway from Eilean an Tighe. Bait (Contrac® blocks containing the anticoagulant bromadiolone 0.005% w/w), was deployed in a grid of 1,183 bait stations covering all areas of the islands and sea stacks. Bait stations were set 50 m apart, with intervals reduced to 25 m in coastal areas of predicted high rat density. Difficult areas were accessed by boat and cliff s of ~120 m in height were accessed by abseiling down ropes made safe using either bolted anchors or ground stakes. The team of staff and volunteers worked through difficult conditions, deploying bait and monitoring intensively for any surviving rats using a combination of tools. The islands were declared rat free in March 2018. This ambitious and challenging project has greatly enhanced UK capacity in rodent eradications for the purposes of conservation.

Since 1999, the black rat (Rattus rattus) has been eradicated from 14 Italian islands, and eradication is ongoing on a further five islands. Most projects were funded by the European Union (EU) Life Programme. Over the years, eradication techniques have been improved and adapted to different situations, including aerial bait distribution on islands with large inaccessible areas, which otherwise would have relied on a manual bait distribution. A priority list of eradications on islands, which was compiled ten years ago, has been met to a large extent, as rats have been successfully eradicated from many islands of great importance to breeding seabirds. Despite some cases of re-invasion occurring in early projects, advances in biosecurity measures have allowed for eradications on islands where this was previously considered unfeasible due to a high risk of re-invasion. This paper reports on black rat eradication work performed on Italian Mediterranean islands with small villages. We show biodiversity benefits of these programmes, but also qualitatively address socio-economic and health impacts on local communities. Eradication projects have faced new obstacles, due to recent changes in legislation which complicated the application of rodenticides and made it very difficult to get permission for aerial distribution of bait on some of the priority islands.