Found a story in the East Anglian reporting that otters are now all over Suffolk. See this link: http://www.eadt.co.uk/news/suffolk_the_rise_of_the_otter_1_2020583
We’re near a tributary of the River Dove, which flows into the Waveney. If an otter caught the carp, it would explain the trail of fish scales and fins between the water and the remains. We’ll be on otter watch from now on.