“What caused extinction of the grayling is still something of a mystery. Destruction of the forest may have changed the nature of their streams too greatly. Log drives coincided with the spawning season and did much damage. Introduction of brook trout may have hastened the end though in England the two species live in the same waters. Overfishing had its influence. Because grayling took the hook readily, to the last fish in a pool, the species is considered unsuited to present day fishing pressure.

A few Montana grayling, a closely related fish if not the same species as some believe, are still planted in Michigan waters by the fish division of the Michigan department of conservation for experimental and sentimental reasons. Planting of about 20,000 were made in 1934, 1935 and 1937. There are now 60,000 fingerlings at Wolf Lake hatchery, hatched from eggs furnished by the U.S. Bureau of Fisheries, which will be planted in the spring of 1940.”    Michigan Grayling Part II @ Fishing for History. Reed Draper re Michigan Grayling