Blog by Dr Steffen Oppel, Senior Conservation Scientist, RSPB Centre for Conservation Science

Sailing a yacht across tranquil turquoise Caribbean waters from one paradise island to the next is the dream that is advertised in many glossy magazines and prize-draws. While soothing and relaxing for the humans who can afford such journeys, boats that hop from one island to the next are one of the greatest threats to the many unique species living on Caribbean islands – because invasive species that could never swim can hitch a free ride.

Photo: Typical tourist brochure of Cayman Brac – one of the most important islands to increase biosecurity.

The islands in the Caribbean harbour a lot of unique animal and plant species, and numerous birds, skinks, lizards or iguanas live on just a single or a handful of small islands. Non-native invasive species that are transported by humans to these islands which they could never reach by themselves, such as rats, cats, mongoose or cane toads, can have huge impacts on native species. Many recent bird and reptile extinctions were caused by invasive species, and there are many islands where we urgently need to remove invasive species to save the unique plants and animals on those islands.

Photo The Sombrero Ameiva (Ameiva corvina) is endemic to Sombrero - an island in Anguilla.

However, removing invasive species is difficult and expensive, and it would be much better to stop invasive species from arriving on islands in the first place. Similar to the human health analogy, namely that prevention is better than cure, properly guarding islands against the arrival of potentially harmful invasive species is often much cheaper and more successful than removing invasive species once they have established. Biosecurity is a term that describes all measures that prevent non-native plant and animal species arriving in a place where they do not naturally occur. But where should we start? Which islands need to be guarded against which animals?

A recent paper by the RSPB Science team explored these questions for >300 islands in the Caribbean UK Overseas Territories. The team focussed on the five most prominent invasive species across the Caribbean (feral cats, brown and black rats, green iguanas and small Indian mongoose), and assessed on which island the invasion of any one of these species would likely have the greatest impact on native vertebrates.

Photo: The potential loss of conservation value on islands in the Caribbean UK Overseas Territories that could result from the invasion of the depicted invasive species. Some islands (like Cayman Brac and Grand Cayman) already have several invasive species, so only small Indian mongoose could invade.

The list of top islands included both inhabited and uninhabited islands in Anguilla, the Cayman Islands and the British Virgin Islands. About half of the 318 assessed islands had no invasive vertebrate species on them and were therefore at risk from any invader, but some islands that are already plagued by rats, cats, and other invasive species could still lose a lot of native biodiversity if the small Indian mongoose invaded – an extremely skilled small predator that can rapidly decimate reptile populations.


Map: Location of the most important islands in the Caribbean UK Overseas Territories where biosecurity needs to be improved to prevent the loss of native biodiversity.

The RSPB is now working with local governments to highlight which islands are especially valuable and what measures would need to be taken to improve biosecurity. Besides tourists coming with boats, the movement of large cargo and construction material is an easy way for non-native vertebrates to get from one island to another. But with tight regulations and proper enforcement the spread of invasive species could be halted before it is too late.