You summed it up Guest, there are many views/opinions, which this thread is about. There are plenty of folks and organizations promoting viewpoints (for a various vested reasons), with little valid science to back them up. I don't believe the person in the site you list has any science background at all? Selecting poorly researched theories and hand picking one convenient research perspective (versus all) to back up a desired result, is a "sketchy" process, IMO.

As I indicated, from reading the science papers, the jury is out on whether seals eat significant quanities of commercial species or not during their various life phases and migrations. Different approaches have been used to learn more. But, all have confounding factors that get in the way.