The big males (at the falls) concentrated on the most nutritionally valuable/potent part of the salmon: the fatty skin and the head/brain. After catching a salmon, they would systematically strip and eat the skin, then the head, and only occasionally the rest of the fish. Younger bears downstream, on the other hand, who were much less proficient at catching fish, ate the entire fish, as well as any skinless carcasses that washed downstream uneaten from the big males at the falls.
What's left after the prime bits are gone. Note how this fish is headless and mostly skinless, either the remains of this bear's catch after he has eaten the best parts, or a carcass he has picked up after a bigger male has eaten the most nutritionally valuable parts.
Another big male peels the skin from a freshly caught salmon.
