Fighting the Battle against Invasive Species in Mauritius
Whether it’s lionfish taking over Caribbean waters or the Australian flatworm devouring native earthworms in the UK, invasive species are a key threat to many species of conservation concern around the globe. Invasives come in all shapes and sizes, but have one thing in common: they spread aggressively and in turn, have the potential to cause harm to natural environments and ecosystems.
The effects of alien invasive species can be particularly damaging to island ecosystems, where there is often a lack of native predators and competitors. Mainland Mauritius is no exception; the country has lost several native reptile species to extinction and a great proportion of the remaining taxa are now isolated on Mauritius’ offshore islands.
In the 1800s, the Telfair’s skink became entirely restricted to Round Island – one of the few remaining areas of the globe that have not been colonised by rats, which are thought have contributed to the skink’s decline elsewhere in Mauritius. Following the eradication of ship rats and feral cats from Ile Aux Aigrettes, the Telfair’s skink was reintroduced to this offshore islet using the Round Island population source in 2006.
With rats out of the picture, the Asian musk shrew is now the key threat to Telfair’s skinks. The musk shrew has posed a significant threat to endemic reptiles ever since its arrival in Mauritius in the eighteenth century. On Ile Aux Aigrettes, the shrews predate on juvenile Telfair’s skinks and compete with the lizards for food resources.
The musk shrew may not be causing widespread devastation yet, but worldwide trade is on the rise and a quick glance at an interactive map of the global shipping network shows just how frequently and widely ships are travelling from landmass to landmass; build in air transport movements, cars, trains, lorries etc., and there would be relatively few areas of the planet that remain unconnected (and so safe from the introduction of non-native and potentially invasive species).
Jamie Copsey, Head of Training for Durrell and co-author of the bait preference paper discussed below, tells me about the issues with invasive species; “we don’t see a species as a problem until it is a problem”, he explains, describing a slow build-up before the sudden negative impact. The question we need to ask ourselves, Jamie says, is “How do we get ahead of the game in this ‘arms race’ to prevent further spread of potentially invasive species?
“Prevention is always better than cure, but once potentially invasive species arrive in new lands, early detection and rapid response is key – we should presume species are ‘guilty until proven innocent’, in order to reduce on-going homogenisation of the world’s biodiversity and loss of biodiversity.”
The case of shrews on Ile Aux Aigrettes is a good example of just how difficult a species can be to remove once it has invaded. Attempts have been made to eradicate the shrew from the islet, but without success. Though it can be controlled at low numbers, the musk shrew has been deemed virtually impossible to eradicate entirely.
Alex Field, a Durrell Postgraduate Diploma student with a drive to improve the current control programmes in Mauritius, designed a pilot project on shrew trapping during his course in Mauritius. “By improving trap success rate” Alex says, “we hoped to decrease the shrew population and allow the threatened Telfair’s skink population to grow”.
The results of the study, which involved trapping shrews around the vicinity of his student house and testing them in a hand-made choice box in the dining room, confirmed that musk shrews prefer a meal of crushed cockroach to peanut butter and oats, and that bait preference is influenced by the presence of musk. Alex hopes that the research will be used to inform the trapping measures used on Ile Aux Aigrettes, with the overall aim of re-establishing native populations and improving biodiversity.
The full study, “Improving capture rate for an invasive species in Mauritius: determining Asian musk shrew Suncus murinus bait preference” was written by A. Field, J. Copsey, C. Tragett, and M. Goder and published in Conservation Evidence in March. It can be downloaded at the following link: http://conservationevidence.com/individual-study/5966
For more information and advice on managing invasive species in the Pacific region, including resource kits for eradicating rodents and cats, visit the Pacific Invasives Initiative at: http://www.pacificinvasivesinitiative.org/
Posted 8 June 2017