The stoat, the cat, and the rat are feared on many islands and even on mainland areas for their effect on native fauna. The swimming abilities of invaders comes it play as soon as we consider efficiency of colonisation. New Zealand has suffered more than anybody from these invaders, starting with the Maoris and then the British! The latter even introduced the stoat to catch rabbits in the 19th century, but scientists in both the UK and NZ warned of the consequences. It seems they told us the truth!
After losing the moas, many flightless parrots and kiwis, owls, eagles, insects and almost the tuatara, the two main islands now protect 250 offshore island nature reserves, particularly from stoats. Assuming the European stoat can swim only 1.5km, wildlife reserves were on the verge of giving up on trapping. This prevents any wetback stoats from being free long in a reserve, but that was before this research by Kim King and her colleagues at the University of Waikato in Hamilton.
She measured the distance that 10 stoats could swim and their level of blood glucose afterwards. This showed clearly how far we need to fix a limit on their abilities, except for one individual. This lady stoat decided to float in the water after an extensive swim, resting her muscles so that theoretically she could begin her swim once more at least and at least double her possible distance.
The results of the research produced one stoat that had a panic attack and was relieved of duties, along with another that had a respiratory infection. Eight more animals survived well and swam from 20 minutes to 2 hours, within distances of up to 1.8km covered.
A water-filled flume provided safe conditions for the stoats, very different from the 3-5km distances that have been swum by pregnant females to invade certain offshore reserves. Male stoats can't be ignored, but stoats can breed, once up to 12 young have been reared from a single female on an island. They have been normally expected to swim a maximum 1.5km, before that happened and this research to check. Stoats are great as little predators and do reduce rabbit populations. It's the human factor that has caused so many alien species to appear in distant parts of the earth to cause so many negative population effects leading to extinctions.
The prolific breeding and early pregnancy of the females combine to combat the short life-span of a predator that is often predated itself. This species can live up to 10 years but rarely breaks through the 1.5 year mark! Now it's up to New Zealand to prevent the alien stoat from achieving what it naturally seeks- prey on small native animals before it is eaten itself.
Carolyn (Kit) King publishes her paper in the journal Biological Invasions.