I'm not sure I support a strict "zero mortality" policy. To my knowledge, seals are not endangered, and they are a major factor in the decline of wild salmon populations in the Pacific Northwest. They congregate in huge numbers for feeding frenzies below dams, estuaries, and other places where migrating salmon are easy pickings. Predator control is certainly no silver bullet, but it should be part of a comprehensive strategy for protecting endangered fish runs.
The act doesnt make sense. If we are so intent on saving mammalian lives, why dont we ban cars, which kill many thousands of adorable deer every year? Human activity sometimes kills animals. You've got to either get over it, or join a vegan commune.
I don't think the act is without merit. Commercial fishing operations shouldn't be allowed to kill countless dolphins and other sea creatures with their driftnets. That's like hunting mosquitos with bazookas and machine guns: http://arago4.tn.utwente.nl/stonedead/tv-series/sketches/fc-21/mosquito-hunters.html