It's an otter & not a young one (worn canines & incisors).....no need for DNA tests, just look at the hind feet..cats & otters don't have the same paws...(or anything else come to that
) & there
IS something to scale it by, ....the grass blades.!
The seagulls are an enigma though, could just be a fox or other predator that knabbed 'em whilst they were nibbling the otter's corpse or more worrying, a poison of some kind
Edit: enlarged photo of hind feet.