Introduced rats are a major problem on Pacific islands. The rats thrive on coconuts but also eat seabird and turtle eggs and hatchlings, as well as invertebrates, and plants. Tetiaroa Society is working with invasive species specialists from around the world to rid the island of this serious pest.
The Tetiaroa Society Conservation and Sustainable Use Plan (CASUP) envisages an atoll where the terrestrial and marine habitat has been restored to as close to its original native form as possible. It is imperative that we do our utmost to allow this and other islands to be as resilient as possible to the future effects of climate change. To that end, the Tetiaroa Atoll Restoration Project (TARP) focuses on the removal of invasive species and restoration of native species.
Rat Eradication and its Consequences
The TARP is beginning with the most significant invasive species on the atoll: the ship rat and the Polynesian rat. These rats severely reduced the native bird population of Tetiaroa, and also feed on green sea turtle hatchlings, plants, crabs and other invertebrate species. With both species of rat successfully removed, Tetiaroa would become a major sanctuary for not just birds but also other native fauna and flora. This would open the potential for transplanting very rare and threatened species from the small remaining populations elsewhere in French Polynesia to Tetiaroa.
Remarkably though, the effects of rat removal don’t stop at the shoreline. The enhancement of the seabird population brings much needed nutrients to the island and the effects from this will cascade down through plant, invertebrate, soil, and marine community ecology. Studies in the Chagos Archipelago have shown that natural seabird populations contribute to the health of the adjacent coral reef. On Tetiaroa the TARP has a chance to record this in real time and develop a model for the sustainable management of tropical islands and their coral reefs in these uncertain times.
Rat eradication is set for August and September of 2020. In order to understand the effects of the removal of a high level predator like rats, baseline data will be collected in all habitats on the island before this date. Surveys will be conducted of seabirds, plants, terrestrial invertebrates, fish, and algae. Transects will be set up to monitor coral and algae cover across the barrier reef system. Water chemistry and microbiome data will be collected from the ground water of the motu to the outer reef. There will also be experiments set up in order to better understand rat eradication in the tropics and that will give researchers insight into how eradication differs if there is more than one species present. This pre-eradication work will be extremely important in order to allow for detailed follow up work for years to come.
In parallel to the main focus on rats, other invasive species would also be targeted for eradication. These include: (i) two species of mosquitoes (a significant nuisance for humans and potential disease vector for all terrestrial vertebrates on Tetiaroa), (ii) one species of biting flies (nonos), (iii) two species of invasive ants (which are major ecosystem engineers like rats).
A research and control program carried out by Institute Louis Malarde and sponsored by The Brando and Tetiaroa Society has successfully controlled one species of mosquito on Motu Onetahi, and is working on other species and control of biting flies on Motu Rimatuu.
The third major component of the TARP would be to follow recommendation from the Flora and Vegetation chapter of the CASUP and work on removing some percentage of the coconut palms that are in unnaturally dense stands due to the farming of coconuts from the 1930s to 1966. This would allow for other native trees and plants to repopulate the motu. Experiments on the removal of coconut palms need to be carried out and monitored to see how best to restore native motu forest.