The depletion of fish is a result of both over-fishing within territorial limits by local small business owners/fisher folk, and the huge factory ships which fish just outside the territorial limits of the richest fisheries around the world, to scoop up everything that is headed out to sea from spawning grounds, etc.

Seals aren't the problem regarding depleted stocks. Humans are. That isn't to say that starving seals aren't a problem, though.

Greenpeace, like every other organization, government agency, or commercial institution, doesn't get right every time. But they are much more on top of this issue than the author of this article.

For a brief overview of the fisheries issues covered at the Earth Summit, this Greenpeace website isn't a bad place to start to look for information:

Global Fisheries Crisis

To suggest that this is a black/white either/or issue is just plain reactionary. The problem is complex. But the reason for the problem sure as shit isn't that seals are eating too much fish.