Hi SJ,
The term "coot" being used as a name for scoter came from the old sea duck gunners in New England......they called scoters "sea coots" or just "coots" for short. The "nick-name" was given because of the dark sooty plumage and the white on the bills of the drakes of the two "most commonly" shot species of scoters; the white wing and the surf (aka skunkhead) were comparable to the plumage and the white bill of coots. But also, in the Northeast, most market gunners didn't often shoot coots because they were not desireable and didn't bring any money for the market, and neither did scoters. Although scoters were shot religiously by avid sea duck hunters in Maine, Massachusetts and the Maritimes, where they were taken and consumed for the gunners table. The meat was dried, pickled, smoked, canned and served just about as many ways as you could imagine.
Hope that helps.
Keith