For you who doesn't know, it a way if foshing, they strap the birds with a small rope around their throat so they can't swallow the fish, only catch it. They can only eat small fish or they get some fish at the end of the fishers day.
Cormorants. They have been used for centuries to catch fish by tying a cord around their necks so they can't swallow large fish, only small fish. The fishermen take the large fish and feed the birds later.