Found only in the cold coastal waters off British Columbia and the wider North Pacific, the sea otter is the smallest marine mammal in North America, yet it spends its whole life at sea. Unlike seals and whales, it carries almost no insulating blubber. To survive in near-freezing water, it relies instead on the densest fur of any animal on Earth, packing as many as a million hairs into a single square inch. For generations the otter was hunted relentlessly for that fur, and by the early twentieth century it had been driven from much of its former range before careful protection allowed a slow recovery.

The sea otter's appetite is as remarkable as its coat. Because it lacks blubber and lives in such frigid water, the animal must eat roughly a quarter of its own body weight each day simply to stay warm. Its diet is built around sea urchins, clams, mussels, and crabs, which it gathers in repeated dives to the seabed. Most striking of all, the otter is one of the few mammals known to use a tool: floating on its back, it will balance a flat stone on its chest, crack a hard shell against it, and let go of the broken pieces once in a while as it feeds.