Atlantic Salmon colonized Lake Ontario from the sea during the last post-glacial period and adapted to life in freshwater conditions. To the aboriginal peoples residing near Lake Ontario, the species was an object of worship and an important part of their diet. European settlers arriving in North America were already very familiar with Atlantic Salmon; records of the species in Europe go back to the time of the Gauls and Romans, and it was granted special protection in the Magna Carta.
Settlers in the Lake Ontario region were able to harvest them by the barrel, and it was an important part of their diet. Some have suggested the availability of Atlantic Salmon encouraged settlement of the interior of Canada. Later, commercial and recreational fisheries for Atlantic Salmon developed on Lake Ontario; the commercial fishery supported thousands of fishermen.
However, it was the pressure of these fisheries plus serious environmental degradation and ecological change that led initially to noticeable and serious declines of Atlantic Ssalmon in Lake Ontario. In the late 1700s and onwards, large areas of land were cleared for agriculture, resulting in a lack of cover for the tributaries of the lake, which were the spawning and nursery sites for the species. Deforestation also created massive erosion problems, which combined with changes in flow rates from dams, mills, and channelization, resulted in the silting-over of the rock substrate where Atlantic Salmon deposited their eggs. Dams and mills also served as barriers that even the legendary “leaping” salmon couldn’t pass during their annual migrations. Meanwhile, in Lake Ontario the fish community was changing. The traditional prey of Atlantic Salmon, lake herring, was being replaced by alewife and rainbow smelt.
As the decline of the Lake Ontario Atlantic Salmon was observed in the latter half of the 19th century, efforts were made to restore or at least maintain the population.