Yes.
The Canadian contingent of the total stock is fished in the summer during the spawning period and the feeding period that follows. At that point, the Canadian contingent is isolated from the American contingent, so the fishery that's happening in Canada is catching only Canadian fish, so to speak.
Conversely, fishing in the United States takes place in the winter, in the area where both contingents of the stock overwinter. That means the United States fishery catches some fish that belong to the Canadian contingent.
In other words, that fishery influences not only the abundance of fish in the American contingent, but also the abundance of fish in the Canadian contingent. That's the important distinction.