That there are sea creatures having the likeness of men and women seems to be generally acknowledged by all who have inquired thereunto , they having found it confirmed by the testimony of many in several countries as their histories do bear. Hence are accounts given of these sea- monsters, the mermen and mermaids, which have not only been seen but apprehended and kept for some time. And hence probably the fiction of the syrens hath had its rise; these enchanting songsters, translated by mermaids by our lexicographers, whose snare Ulysses so happily escaped.
They tell us that several such creatures do appear to fishers at sea, particularly such as they call sea-trowes, great rolling creatures tumbling in the waters…… the fishers in Orkney and Zetland are afraid when they see them, which panic fear of theirs makes them think, and sometimes say, that it is the devil in the shape of such creatures; whether it be si or not as they apprehend, I cannot determine. However, it seems to be more probable that evil spirits frequent both sea and land.
John Brand, A Breif Description of Orkney, Zetland, Pightland-Firth & Caithness, 1700