Amsterdam Island’s ecosystem soon to be free of introduced animals

L’Amsterdam Island, which is part with Crozet and Kerguelen of the French Southern and Antarctic Lands (Taaf), will undergo in 2024 an operation to eradicate introduced animals, cats and rodents, whose presence inflicts a lot of damage on the ecosystem.

After centuries of voluntary or involuntary introduction of mammals and exotic plants by humans in the Southern Lands, the nature reserve created in 2006 must restore a balance on these very fragile sub-Antarctic islands. Even if it means taking difficult measures to eradicate or limit invasive species, such as rodents, rats and mice, feral cats – domestic cats returned to the wild – reindeer or rabbits.

In Amsterdam, “the Reci project (restoration of island ecosystems in the Indian Ocean) aims to eradicate rats, cats and mice by winter 2024”, explains Lorien Boujot, technician for the management of introduced mammals. in Amsterdam, to the environment department of Taaf.

“Cats and rats, since they were introduced in Amsterdam, have been the main cause of the disappearance of a dozen species of nesting birds, he says. Rats tend to + predate + eggs or even chicks , and cats can attack animals in the adult stage”.

In addition, “Rats are carriers and vectors of the fowl cholera disease. It is likely that this disease was brought to the island when there was a chicken coop and now it is decimating year after year the reproduction of the yellow-billed albatrosses, present on the cliffs of Entrecasteaux”, in the south of the island, adds Lorien Boujot.

Mice have a big impact on vegetation.

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“They eat a lot of inflorescence and seeds of native plants like Phylica, a shrub that formed a belt all around the island and for which natural regeneration is almost non-existent”. Agents are trying to replant young Phylica, but “rats tend to eat and break young plants”, underlines Lorien Boujot.

Eradication at 2 million

The eradication operation planned for the austral winter of 2024 will consist of two aerial spraying operations over the entire 55 km² island, which is very rugged, three weeks apart. “The difficulty is that if we miss a rodent’s vital area, the operation is a failure”, indicates Lorien Boujot.

“Since 2017, preliminary studies have been carried out to better understand the target species. Above all, it is important not to intervene in full reproduction because there is a risk of young people remaining in the hole who are not affected by eradication methods”, insists- he.

The Reci project also provides teams on the ground to perhaps eradicate the last cats present, by trapping and shooting, specifies Mr. Boujot.

Equipped with a hunting license, the two field agents specializing in “introduced mammals”, Louis Gillardin and Brieuc Leballeur, are responsible for this difficult task for the 2023 wintering season.

“Last year our predecessors eradicated seven + individuals + and it’s been a month and a half, two months, that we haven’t seen any more on the forty photo traps. We think that potentially there could be one to five left” , says Louis Gillardin. And to add: “I’ve never killed a cat in my life and if that happens, it won’t make me happy… If they had disappeared, it would suit us!”.

According to Brieuc Leballeur, ornithologists note that there is less mortality of chicks since he installed rat traps around the colony of yellow-nosed albatrosses. “The preservation of ecosystems” is the meaning of all this work, he notes.

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At the end of the 2024 eradication campaign, it will be necessary to wait two years without detection to say that the operation is successful, and “at the end of ten years” the return of the species of birds which had ceased to nest. in Amsterdam, says Lorien Boujot.

Jérémy Tornos, a CNRS researcher in eco-epidemiology, is eager to see this operation completed, for the well-being of the birds. And particularly for the colony of Yellow-billed Albatross in which “a drop in chick survival has been observed since the 1980s”.

After eradication, “we will be able to see the impact of the rat, predator and pathogenic source. We do not know if rats are carriers of avian cholera and transmit it to the birds they bite or if they are carriers because they eat carrier birds. A colony without rats will also test the true effectiveness of the vaccine” against this disease, hopes the researcher.

But this model is not possible to replicate on all the islands, despite the ravages that rodents and feral cats also cause in Kerguelen, not to mention rabbits and reindeer.

“These are very heavy actions to put in place. Eradication in Amsterdam is a budget of more than two million euros which mobilizes a team for years. We cannot carry them all out at the same time”, assures Clément Quetel, Deputy Director of the Taaf Environment Department.

In Kerguelen, “projecting the eradication of the mouse, which is present almost everywhere, is just impossible from a material, financial, human and logistical point of view, he says. Eradicating the Kerguelen cat, not feasible either in So, rather than doing eradication, we do limitation” with targeted “trapping and shooting” actions.

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Then, it will be necessary to ensure that rats and mice do not return, in particular thanks to human activities and therefore to apply a “biosecurity” policy. Kevin Nory is thus responsible for monitoring that the ship Marion Dufresne, supplying the bases four times a year, does not become a vector of transport from its home port in Reunion or from one island to another.

He works at the level of suppliers, the forwarding agent, at the quay before boarding then in the districts.

Sinking into the bowels of the ship, Kevin Nory also regularly monitors whether the rat poison has been eaten, in about thirty boxes. He manages the removal of household waste from the bases, which must arrive on the boat in airtight containers.

“Rather a good sign”, he has found no trace of rodents on the boat since mid-2021.

10/01/2023 10:14:48 – Île Amsterdam (France) (AFP) – © 2023 AFP

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