It seems that these are Asian or Oriental Small-clawed Otters, Aoynx cinerea, the world's smallest otter. They form small family groups and defend them strongly against non-family intruders. The Codger informs that zoos get into trouble when they try to introduce new members to a group. The newcomers often received fatal injuries or lost limbs.
This is the pond harboring the group of otters. I counted nine with several juveniles amongst them.
Otters are often inquisitive and members of the group kept a close watch on those oddballs on the bank.
The group was actively feeding and although they are known to prefer shellfish rather than fish, I saw them feeding on what appeared to be catfish.
I was a considerable distance away from the group but you could hear them crunching (or crushing) their food. I now believe they were crunching on some sort of shellfish at least part of the time.