Thanks for the excellent reply. The salmon season in Quebec runs from June 1-September 30. In New Brunswick, the "bright" season is June 1-October 15 with considerable discussion right now about extending it to October 31.
In Nova Scotia, the season is June 1-October 31. With the exception of 2-3 rivers on the south shore, Nova Scotia has become more of a "back-end" fishery: the majority of the fishing is in the Fall on rivers that flow into the Northumberland Straight.
In Quebec, early season water temperatures are in the mid to upper forties; during the peak of the run (late June/early July), temps are in the mid-fifties.
Miramichi fish seem better adapted to warm water than other strains of salmon. Good fishing often occurs with water temperatures well into the sixties.
Fall fishing in Nova Scotia sees water temperatures in the 42-48 degree range. The best month is October: temps are generally 42-45 at that time.
Richard Waddington viewed a water temperature of 48 degrees as the decisive mark below which he fished a sunk line. Waddington approached salmon below this critical figure almost as a separate species. I'm with you: I think 45 degrees is closer to the watershed temperature.
It is impossible to account for the broad range of salmon behavior in a single post. One must also temper one's remarks with a view towards their possible misinterpretation and potential misapplication.
There is a quiet movement afoot to ban or severely limit the use of sinking lines in Canada (see the current issue of the Atlantic Salmon Journal). The argument is as follows: if weighted flies are illegal (except in Quebec), why not ban sinking lines which allow the fly to be presented at the same depth?
As always, it seems that the misadventures of a ruthless few (i.e. foul-hooking) ultimately define the parameters we all must follow......