The Manx fishermen, when out on the sea, used to call the merman ‘yn guilley beg‘ (the little boy). This was his ‘haaf‘, or sea name, by which alone he was allowed to be alluded to on the sea; his land name is ‘pohllinagh‘.
There were many other words which were tabooed by the fishermen while engaged on the sea, and the same custom was followed by the Shetlanders and the Scottish fishermen. Even the surname was changed at sea by the men, and I could quote some instances to that effect.
Mermen and mermaids have been known sporting and gambolling around the creeks and coves on the south-west part of the Island, and I have heard many a tale about their doings – and as I was told by an old friend: –
“When they saw him they made a cake of oaten bread and butter and threw it out. I have heard of a man that came on one of them on the shore, and put him in the sea again. After that, when there was a storm near, the merman was always coming to inform him, and he was not caught in a storm as long as he went out to sea.”
(source: Manx Notes & Queries (1904) edited by Charles Roeder; artwork http://bit.ly/1hBNixl)