Scientists investigate impact of Samoa rat eradication project
Updated
Scientists are investigating how plants and animals were affected by the rat eradication project on the Aleipata Islands of Samoa last year. The project is run by The Secretariat of the Pacific Regional Environement Program.
Presenter: Geraldine Coutts
Speaker: Dr Alan Tye, SPREP Invasive Species Officer
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TYE: The project was to eradicate Pacific rats from two offshore islands, the main island of Upolu, and that was done in August-September last year by dropping poison bait from helicopter. So the work now is really monitoring to see whether that was successful and the effects that's had on the native plants and animals.
COUTTS: Well how much have you learned so far Dr Tye?
TYE: We've done some post-eradication monitoring already with a trip to monitor lizards, one of the things that's impacted by the rats are native skinks and geckos, so that's already been done. We're also monitoring the vegetation, we've got permanent photo plots and bird counts, which the follow-up ones haven't been done yet, we did a pre-eradication bird count, and some invertebrate monitoring too.
COUTTS: Have you had any losses that you didn't want because of the rat poisoning program?
TYE: No it went better than we expected. We actually caught 26 friendly ground doves which are restricted to those off-shore islands in Samoa these days, and they've become virtually extinct on the main islands. And we kept those in captivity in case they would be affected by the rat poisoning. But there were several doves left on the islands which survived, we didn't find any dead doves on the island and we put the others back afterwards and they were fine. We did have a couple of rails like the New Zealand Weka ate the bait and died but most of those also survived, they're common on the islands and common in all of Samoa's islands. So that loss of one or two individuals there was not a problem.
COUTTS: You basically produced a rat-specific bait for this project?
TYE: That's right, it's a cereal-based bait that breaks down very quickly in humid weather like we have here within five days after the first bait drop, and the bait had pretty much disappeared or virtually all disappeared. So it's designed to attract, it's coloured bright green so birds don't find it attractive, it doesn't particularly smell attractive to anything other than rats, and there are no other non-target animals on the islands that would really be attracted to the bait.
COUTTS: Well most animals and bugs and insects and stuff have their job and a reason for their pecking order in the animal kingdom. Does the rat actually have a positive job that will be missed on this island once and if it is totally eradicated?
TYE: No it's pretty much all negative in this case. It eats seeds so it interferes with forest regeneration, it eats seedlings of trees as well and so it stops them regenerating, it eats birds eggs, young chicks, lizards, invertebrates, so it's damaging all of those elements of the ecosystem and it doesn't provide anything positive. There's nothing really on the island that would eat rats, so nothing benefits from the presence of the rats at all really.
COUTTS: And I think last time we spoke we also looked at mongoose that were found in Samoa and they weren't sure whether there was a mating pair or they were single or more, what do we know about that situation now?
TYE: They've only caught one thankfully, but the traps will be out for at least a year, if we don't catch another one after a year then we'll probably be confident enough to declare the animal eradicated. So we're still hoping that there's only one, we caught one male.
COUTTS: Ok and just as we finish off this morning doctor, the invasive species happening in the Pacific, are they abundant?
TYE: Oh yes far too abundant, it's a big job. We don't have the resources to tackle them all, really just focussing on the top priorities.
COUTTS: And what are they?
TYE: Rats are one of them actually widespread because of the damaging effects they have, they're a predator and there are no native mammalian predators on Pacific Islands. So they're really one of the top targets.
