For two minutes at a time otters plunge beneath the surface to find urchins, abalone, and sea stars. One of the few animals to use tools, an otter will pick up a sea urchin and a small rock from the seafloor. Once back at the surface, the otter rolls onto its back, places the rock on its chest, and smashes the urchin against the rock until its shell is broken.

Sea otters were nearly wiped out by fur trappers by the early 1900s. Still listed on the U.S. Endangered Species List, the sea otter is making a comeback, thanks to international protections—and to marine sanctuary designations for critical otter habitats, such as Monterey Bay.

The smallest species of marine mammal, sea otters are closely related to weasels. Unlike every other marine mammal, sea otters have no blubber, so they must maintain a high metabolism by eating some 15 pounds (7 kilograms) of food a day—about 25 percent of their body weight.