User blog comment:Kogath/Monster Hunter X Discussion/@comment-5020152-20150808212626/@comment-25119729-20150821223244

Actually, Plesioth is made more for speed than combat, given that the only good defense it has is its water beam, which is useless against pretty much anything that also lives in water. Interesting to note here is that the ecology pages notes that they can swim faster than Leviathans, which to me seems like they prefer to simply outswim predators, rather than fight. Also, Draco just pointed out that they do this in tropical waters, not the Snowy Mountains.

Last but not least, the first area of the Snowy Mountains has a huge lake, with good acces to the colder regions. It wouldn't be to off if a Zamtrions would use the lake as its home to go into the mountains in search of prey and then return.