Sunning themselves on rocks or waddling awkwardly across the beach, it's easy to think of these immobile mammals less as sea lions, and more as sea house cats. But don't be fooled by their beachside behavior.
Under the waves, sea lions are incredible endurance hunters, hurdling around at speeds of 4 to 18 mile an hour and hunting for up to 30 hours at a time, these majestic mammals live up to their name. And thanks to a suite of physical adaptations, finely tuned over millions of years, they make for resourceful foragers.
To find their favorite food, sea lions hunt much deeper than many of their semi-aquatic peers. With some species diving to depths of nearly 400 meters, they're able to cope with the mounting pressure by collapsing their pliable rib cage, and compressing a pair of springy lungs.
This pushes air up through the smaller airways, collapsing rings of cartilage as oxygen travels out from the lungs, to be held in the larger, upper airways. Upon surfacing, this air will be used to re-inflate the lungs, but for now their heart slows down to preserve oxygen.
Blood flow is redirected towards only the most essential organs like the heart, lungs, and brain, which rely on reserve oxygen stored in blood and muscle. Once they arrive at their hunting ground, sea lions depend on their superior vision to find their prey.
Most mammal eyes have a structure called a lens—a transparent, convex structure whose shape refracts light to enable sight. In humans, this lens is curved to process light waves traveling through air.
But sea lions need to see their best at hundreds of meters deep. To accommodate, their eyes have a much rounder lens to refract light underwater, as well as teardrop-shaped pupils which can expand to 25 times their original size.
This lets in as much light as possible, helping them pinpoint their prey in even the dimmest conditions. But once they've closed in, they rely on something akin to a sixth sense to actually catch their meal.
Their whiskers, or vibrissae, are composed of keratin and full of nerve fibers that run deep into the connective tissue of their face. Sea lions have full directional control over these whiskers, which can lie flat against their face, or stick out at a 90-degree angle.
When properly tuned, these whiskers can sense the slim trails of moving water that fish leave in their wake. And they're precise enough to let blindfolded sea lions tell the difference between objects less than two centimeters different in size.
