Read the excerpt from "Killer Whales and Great White Sharks.”Both killer whales and great white sharks have important jobs in nature. Because they hunt and eat other ocean animals, they keep the ocean from being overcrowded. Sharks help keep the ocean clean by eating dead animals they find. Both killer whales and sharks are valuable to the environment. They are also unique creatures that fascinate humans. We have learned much about the workings of nature by observing these magnificent animals.