Frank ,has touched on it before & It rang true with what I think is happening around me , these otters are not territorial they've been reared with other otters , lots of them at that in big open fenced pens . Wild otters would fight each other to the death to keep there territory , survival of the fittest & all that . This new population seem happy to feed along side each other as that's what they know & it's obvious it's been passed on to the next generations , hence how quickly a lake can be emptied, well that's my take on it around me . We are in an area where the legal reintroduction is taking place .
Like you say nothing natural about it .