You raise some very interesting points, as always.
With the virtual elimination of a commercial fishery for Atlantic salmon of North American origin, many rivers experienced a significant bump in numbers of returning fish in 2003 (@ 20% and upwards for some systems).
The elimination of the commercial fishery also gives the North American angler the dubious distinction of killing more Atlantic salmon than all other user groups combined: an interesting dilemma for sportfishing conservation organizations at the bargaining tables of the future.
For some interesting commentary on drift nets, see: www.atlanticsalmontrust.org
under "News." The Atlantic Salmon Trust is a non-profit organization and a registered charity based in the U.K.