I'm wondering if that is about all there is left for them to eat. My mate thinks the pike and perch it used to have have been killed off by eutrophication (resulting from masses of goose poop). There were at least some sticklebacks, but maybe not enough to sustain 2 or possibly 3 otters for very long. There were ducks and other waterfowl when they arrived, but they all scarpered when they realised they were being attacked and eaten. The otter was doing a lot of crunching and chewing. I thought this was it trying to chew the spines off sticklebacks, but looking at the shots I got where you can see into its mouth, all I can see is black gunge?
I wondered if they were having to resort to eating snails?
I'll see if I can find my mate's shot with a fish...
I have very similar shots as this one from the Almond Otter, and always wondered what it was feeding on, apart from the occasional trout and one salmon i have still to make out what it is eating, I have watched the otters on the Clyde eating fresh water mussel's and the obvious crayfish, one with a large pike and an odd big trout, so could be snails Col.