Hello and thanks for the welcome.
I remember that book from being at junior school and I remember a film from the 70s.
The otter is an interesting character in Celtic myth and folklore. The Irish have tales of the fearsome Dobhar-chú or King of the Otters and, of course, it is one of Ceridwen’s transformations.
My own view is that the otter is one of those liminal creatures, it lives in sacred waters and on land, it eats salmon (!) and it has a very “snaky” movement, especially in water. The English, Latin and Greek words come from the same origin as the word “hydra”, it makes you wonder if the ancient legends of water-serpents might not have actually been about otters. Who knows?
I’m far from an expert, but from a bit of reading I’ve done, I’ve read that otters were sacred animals in Ancient Iran (Persia) along with dogs, hedgehogs, weasels, foxes, beavers, starlings, crows/ravens and vultures. Some familiar animals there from Celtic myth too, aren’t there? Apparently, killing an otter was considered a terrible crime and, interestingly, although hunting the otter was permitted in Scotland, it seems to have come at a great risk and potential price if you fell foul of the Otter King.