Admiralty Sailing Directions dating to 1870 note the tradition of pasturing sheep on the island - 'the two islets Ynys Gwylan (Gull islands); they are mere rocks, affording pasture to about a dozen sheep'.
Sources include:
Admiralty, 1870, Sailing Directions for the West Coast of England from Milford Haven to the Mull of Galloway including the Isle of Man, pg64
