These are Pacific salmon juveniles. The adults have spawned, the eggs have hatched, and the fish spend about one year in a lake. They then migrate down the Fraser River, go into the ocean, where they spend two years, and then they come back as adults.
When the fish hit the ocean in 2003, we know that the ocean surface temperatures were unusually warm--one to three degrees above normal. Even though that may sound modest, across the north Pacific it's hugely significant. Those kinds of temperatures change predator-prey relationships and make conditions different for Pacific salmon. It's possible that those fish hit the waters when the conditions weren't optimal and as a result they suffered unusual mortality. When they came back, we didn't see the numbers. We did not get the survival rate you would have otherwise expected.