Slate Islands (Ontario)
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The Slate Islands archipelago is formed of two main islands, five minor islands and numerous islets located in northern Lake Superior south of the town of Terrace Bay. The total surface area is about 36 km². The nearby 'Leadman Group' of islands one km east is often considered part of the Slate Islands.
The islands are home to woodland caribou which have been studied extensively from 1974 to today by Dr. A.T. (Tom) Bergerud. The caribou are a classic example of island biogeography in action; the islands are notable for species that are absent but present on the adjacent mainland (red squirrel, moose, white-tailed deer, and grouse). No ungulates were present on the islands until the caribou arrived in the early 1900s. And, no predators of caribou were present. Caribou reached and maintain higher density than anyplace in the world here. Wolves reached the archipelago in the early 1990's preying heavily on the caribou but for reasons not entirely known they disappeared a few years later. Other mammals found on the islands include beaver, muskrat, snowshoe hare, short-tailed weasel, red-backed vole, and red fox.
A lighthouse was built on Patterson Island, the largest island, in 1903 to help ships locate the harbour at the nearby town of Jackfish, Ontario.
The original forests on the islands were modified by logging and forest fires. Up until the 1940s, the islands were used to stockpile boomed logs from the mainland Lake Superior north shore for export on lake freighters to pulp mills in the United States.
The outer shores of the Slate Islands are particularly harsh habitats and harbour arctic plant species. These arctic disjunts are reminders of ice ages and associated tundra conditions in this area in the past.
In 1985, the Slate Islands were protected as an Ontario provincial park. There are no facilities and the islands can only be accessed via boat or airplane. The islands remoteness is enforced by almost 9 km of open, wild, Lake Superior water and its distance from any large communities. It is frequented by naturalists, fishing parties, sailors exploring this Great Lake, and recently by an increasing number of sea kayaking parties.
The waters of the Slate Islands have been protected even longer from commercial fishing to preserve one of the last native stocks of lake trout in Lake Superior. The Slate Islands have been a source of lake trout brood stock used at the Dorion Fish Hatchery, and fingerlings are planted back to Lake Superior to restore the fishery.
The islands are believed to have formed as the result of an uplifting of material in the centre of a meteor impact. The islands are not made of slate, mainly consisting of metamorphosed igneous rock.
The Slate Islands impact crater is 30 km in diameter and its age is estimated to be about 450 million years (Ordovician).
