1. The seals eat codfish and others because that is their NATURAL PREY. It is what they are MADE to eat. They don't have a choice. We do. That's why we breed animals to eat.
2. Commercial fisherman collect far more fish in their nets than the seals eat, and some have abused the priviledge grossly; thus depleting fish stocks at a rate the seals couldn't hope to match.
3. Rather than admit the problem in 2, which would require actions on their part to conserve the stocks (as New England fisherman have done, to their profit and benefit), they take the easy (and cowardly) way out and blame the seals.
4. By blaming the seals (for eating their natural prey), they have an excuse to brutally slaughter their young (note: they do not kill the ones who ACTUALLY EAT THE FISH, the adults) so they can sell the pelts.
5. They do so allegedly to offset the "loss" of the depleted fishing grounds, completely ignoring their OWN role in it. Cleaning your own house first, anyone?
6. The Canadian government tolerates this because otherwise, they would have to either a) pay the fishermen welfare; or b) admit the problem of overfishing themselves and take steps to limit it.
7. Due to #6, the whole thing, in addition to being completely depraved and sleazy, also has the bonus of constituting welfare.
Blaming a seal for doing what seals are born to do is like blaming a cat for preferring the taste of mice. Seals do not in any way threaten the survival of the human race by their preference in food. Using the animal's natural instincts as an excuse to profit from its inexcusably brutal slaughter is, to put it politely, sleazier than a Harlem crack-whore.