The Treaty of Paris, 1763
The question of access to the Newfoundland fisheries was one of the most difficult issues to settle during the peace negotiations which ended the Seven Years' War. The French government was determined to maintain a fishery in the region. Its negotiators asked Britain to allow the French to catch and dry fish in the Gulf of St. Lawrence, and on the Newfoundland French Shore as defined in the Treaty of Utrecht (1713). In addition, France wanted a base ("abri") for its banking and offshore fleet, and suggested that it might keep Cape Breton for this purpose.
The British government was initially divided between those who wanted to drive the French out of the fisheries altogether, and those who were prepared to compromise. In the end the compromisers won the argument, and France got substantially what it asked for.
Why was this? Put briefly, the concept of total war did not exist in the 18th century, and wars were fought not so much to crush opponents, as to readjust the balance of power. Britain did not aim to destroy France in the Seven Years' War, and the government recognised that, to France, access to the Newfoundland fisheries was a vital national interest. Having established control over North America, Britain was prepared to concede a share of the fishery to facilitate the making of peace.
In the final settlement, France was permitted to continue fishing on the French Shore and in the Gulf, and was granted the islands of St. Pierre and Miquelon as a fishing base. But the British insisted on wording by which France undertook not to fortify the islands, and not to turn them into a military base. Though dissatisfied at the time, and humiliated by the conditions attached to the transfer of St. Pierre and Miquelon, France had in fact retained what was essential to maintain its migratory fishery.
Article 5. The subjects of France shall have the liberty of fishing and drying, on a part of the coast of the Island of Newfoundland, such as is specified in Article 13 of the Treaty of Utrecht; which article is renewed and confirmed by the present Treaty (except what relates to the Island of Cape Breton, as well as to the other other islands and coasts in the mouth and in the gulf of St. Lawrence). And His Britannic Majesty consents to leave to the subjects of the Most Christian King the liberty of fishing in the gulf of St. Lawrence, etc.
Article 6. The King of Great Britain cedes the Islands of St. Pierre and Miquelon, in full right to His Most Christian Majesty, to serve as a shelter to the French fishermen; and His said Most Christian Majesty engages not to fortify the said Islands; and to erect no buildings upon them, but merely for the convenience of the fishery; and to keep upon them a guard of fifty men only for the police.