The herring fishery was by far the most important of all the sea fisheries, and as this fish was found in greatest abundance on the British coasts, foreign fishermen were attracted hither in great numbers. It was with reference to the herring fishery that exclusive claims were raised by England in the seventeenth century, and it is desirable at the outset to understand the policy which was pursued previously in regard to it both in England and Scotland. At what period foreign fishermen first began to frequent the British coasts is uncertain; but we know that within fifty or sixty years of the Norman Conquest fishermen from Flanders and Normandy--and doubtless from other countries--visited our shores and carried on a fishery for herrings by means of drift-nets. An important fishery was established at the mouth of the Firth of Forth, on the east coast of Scotland, in the early part of the twelfth century, and it was shared by fishermen from England, Flanders, and France, who paid tithes to the monks of the priory on the Isle of May. This monastery was founded by King David I. before the middle of the twelfth century, and was endowed by him with the manor of Pittenweem in Fife, and by Cospatrick, the great Earl of Dunbar, with a house and “toft” at the village of Dunbar, both grants being of value in connection with the fishery. King William the Lion (A.D. 1165-1214) confirmed these grants, and addressed missives to “all his good subjects and the fishermen who fish round the Isle of May” commanding them to pay their tithes to the monks as they were paid in the time of his grandfather, King David (A.D. 1124-1153); and he prohibited them from fishing in their waters or using the island without license from the monks.[99] This very early claim to the right of exclusive fishing in the sea is characteristic of the policy of all the Scottish kings. It was repeated on several occasions, the royal mandate being sometimes addressed solely “to all fishermen who fish around the Isle of May”; and that some of them were foreigners appears to be shown not only by the statement above given, on the authority of contemporary monks, but by the size of the vessels, some of which had four hawsers, and paid much higher dues at the neighbouring harbours than the local fishing-boats. We know also from contemporary Flemish records that as early as the first half of the twelfth century fishermen from Nieuport and other places in Flanders fished from large vessels for herrings with drift-nets in August and September in the northern parts of the North Sea.