Disagreement exists in the literature as to whether lake trout survived Wisconsin glaciation north or south of the ice sheet. Other freshwater fishes whose range in North America equals or exceeds that of lake trout all survived in both northern and southern refugia. Arguments in favour of a southern refugium for lake trout include their wide distribution eastward to Nova Scotia and New England, their presence in some Mississippi headwaters, and possible late-Wisconsin date of a fossil lake trout south of glaciation. Absence from some habitable lakes along the southern margin of glaciation is attributable to northward shift of isotherms during the hypsithermal period. A northern refugium is suggested by occurrence of lake trout in remote parts of Alaska, and the improbability of their having failed to reach and persist in Alaska prior to last glacial advance. They do not now closely approach Bering Strait, and may be held in check by ecological factors which have been operative also during previous glacial and interglacial periods, on the Bering land bridge as well as on the continent. Hucho taimen is a related Asian counterpart whose dispersal may be similarly controlled. Large lampreys may prevent dispersal of lake trout into lower water courses and the sea.
THREATENED FISHES OF THE WORLD: Hucho taimen (Pallas, 1773)
