The Slate Islands are a small archipelago in Lake Superior, Ontario, Canada, about south of the town of Terrace Bay. The island group, consisting of 15 islands in total, was created by a meteorite impact which formed a crater about wide. In 1985, the Ontario government established the Slate Islands as a natural environment provincial park. The islands are notable for having Ontario's largest herd of boreal woodland caribou.
Geography
The island group consists of two main islands (Patterson and Mortimer), five minor islands (McColl, Edmonds, Bowes, Delaute and Dupuis islands) and numerous islets.
The total surface area is about .
The nearby Leadman Group of islands, about east, is often considered part of the Slate Islands. This group includes Leadman, Cape, Spar and Fish Islands. They have been studied extensively from 1974 to 2007 by 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 while predators have been present only sporadically. Caribou reached the highest population density in the world on the islands before the 1990s, with the herd estimated at 650 animals. After a food shortage and die-off in 1990, the numbers were reduced to about 100. Wolves reached the archipelago in the early 1990s, preying heavily on the caribou, but for reasons not entirely understood, they disappeared a few years later. Wolves are again present on the island since winter 2015/16 (or earlier) as evidenced by aerial observation and scat.
The waters surrounding the Slate Islands have been protected from commercial fishing to preserve one of the last native stocks of lake trout in Lake Superior. The 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.
Species
Mammals found on the islands include woodland caribou, grey wolf, beaver, muskrat, snowshoe hare, red fox, meadow jumping mouse, and little brown bat. Dryas drummondii (not found again for 1600 km (1000 mi) north),
The youngest rocks are diatremes, referring to breccia-filled volcanic pipes that were formed by gaseous explosions. They occur as dikes or sills which criss-cross the all older rocks types. Another source estimates the age at 800-500 million years (late Proterozoic to early Paleozoic). It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event, including the Decorah crater in Iowa, the Ames crater in Oklahoma, and the Rock Elm crater in Wisconsin.
Provincial park
The Slate Islands Provincial Park was established in 1985 to protect the biodiversity and provincially significant elements of the natural and cultural landscape, and to maintain the islands' ecology by controlling development and focusing recreational use.