Ichthyofaunal surveys of the Huron Mountains and Isle Royale, Michigan, and the Sibley Peninsula, Ontario, allow for both a comparative study of colonization events and the effects of sequential isostatic rebound within a large portion of the western Lake Superior basin. The distribution of some fish species in these areas is the result of catastrophic events related to glacial retreat. The highest Huron Mountain lakes were colonized during channel events occurring shortly after the Marquette readvance began its retreat. Some species present on the Sibley Peninsula were likely carried by overflows from Lake Agassiz. Most lakes within these areas, however, were colonized well after 9700 BP, when large numbers of species had gained entrance to Lake Superior, mainly from Mississippi basin refugia. Several species, presumably because of earlier warming periods, had a wider distribution than they exhibit today. Some colonization of Isle Royale was probably through the straying of a few individuals from these populations. Lake Superior remains a formidable barrier to many species, restricting them to favourable areas within the western basin.
