It is a predestined collision of two massive migrations - a David versus Goliath event - when thousands of ravenous salmon sharks gather to attack millions of Pacific salmon. The salmon are desperately trying to reach their spawning grounds in Prince William Sound. The sharks are there to gorge themselves. But sharks? In Alaska? Of the nearly 500 known sharks in the world, this is the only large, agile shark equipped to ply these icy waters. This shark is warm-blooded. In the end, the salmon run on an urgency born of their need to reproduce while the sharks they run on primal hunger.