User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-68.49.124.68-20130204051221/@comment-5963861-20130207004559

Deviljho's tail is not built for swimming it is for balance like any other theropod. While it possibly could paddle by using it's legs it probrably wouldn't be able to do this for long periods of time. Now concerning the Deserted Island my theory is that it isn't a lone landmass, but part of an archipelago which is an island group or island chain. This grants the creatures to travel to and from the area as non-flying creatures can make short trips across the ocean, instead of making an hour or even longer distance trips.