Seychelles Island Foundation: Aldabra Rat and Cat eradication

 Invasive alien species (IAS), such as rats and cats, have significant negative impacts on island ecosystems. These impacts lead to population declines and high rates of extinction of native island species. The severe degradation of ecosystems by invasive mammals reduces the ability of these ecosystems to adapt to and recover from the impacts of climate change. Eradication of invasive mammals from islands is therefore a crucial nature-based solution to boost ecosystem-based adaptation to the impacts of climate change. The Seychelles Islands Foundation (SIF) are currently conducting a feasibility study to gain the site-level knowledge required to prepare for a large-scale rat and cat eradication on Aldabra Atoll, Seychelles, which will be the second largest mammal eradication in the tropics.

Aldabra flightess rail

Aldabra is a Key Biodiversity Area (KBA), a UNESCO World Heritage Site, a Ramsar Wetland Site, and a large-scale Marine Protected Area (MPA), hence an important site for biodiversity in the Western Indian Ocean. It is home to many native and threatened species, including the world's largest giant tortoise population, the largest frigatebird population in the Indian Ocean, and one of the largest turtle populations in the region. It also has the largest coral reef systems, seagrass beds, and mangrove forests in the Seychelles archipelago, all of which play a major role in blue carbon storage. Recent research has shown that the atoll is a key source for coral larvae across the region, and may also play a role in the connectivity of other taxa such as mangroves and fish.

Rodents caught by camera trap raiding the ground nest of a tropic bird. 

SIF has identified the eradication of rats and cats as the single most important conservation action to enhance the atoll's critical ecosystem functions and services, and to support its adaptation to climate change. SIF have developed a world-class biosecurity system for Aldabra, the culmination of a decade of work, research and additional projects. With this in place SIF are confident they can proceed with an eradication with minimal risk of re-invasion.

Why is eradication so important at Aldabra? It is becoming clear that land-ocean connectivity plays a crucial role in the resilience of marine ecosystems. Aldabra, with its mosaic of coastal habitats, including mangroves, seagrass beds, coastal forests, and coral reefs, provides a range of ecosystem services that are important for climate change adaptation, such as coastal defence, carbon capture, primary productivity, nutrient cycling, shading and watertable stability. Aldabra is therefore in an excellent position to improve understanding of both these connections and the potential of eradication as a nature-based solution. However, despite its high biodiversity and protection status, Aldabra’s ecosystem is not intact and it remains extremely vulnerable to climate change and invasive species threats.

Grand Pass, Aldabra atoll

An example of land-ocean connectivity boosting resilience comes from recent ground-breaking research in the Chagos Archipelago which showed that reefs next to rat-free islands (with seabird densities 760x higher than islands with rats) recovered more rapidly after bleaching events and had 25% faster-growing, richer fish communities with 50% higher biomass, due to seabird-derived nutrients that promoted coral growth (Graham et al. 2018). Hence, as coral bleaching continues to threaten tropical reefs and increases in frequency and severity due to climate change, the eradication of invasive mammals on islands will be an important way to build the resilience of these ecosystems. This is especially relevant for Aldabra, which has such a large and well-connected coral reef ecosystem.

 Noble Caledonia has been visiting Aldabra and the Seychelles for over 20 years. We were proud sponsors of the Aldabra plastic clean up. This ambitious RACE project is something we are proud to support and have pledged £5 000 in 2024 to get the funding started.