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. Hurtling around at speeds from
4 to 18 miles 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 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. With these tools a healthy sea lion can
catch generous helpings of fish such as anchovy, mackerel,
and squid on every outing. And with their exceptional memories, they
can remember multiple hunting grounds, including those they haven’t
visited in decades. This memory also extends to breeding
territories and birthing areas, as well as which neighbors
are friend and foe. There’s even evidence that sea lions
can remember how to perform tasks after 10 years with no
practice in between, letting them navigate old stomping
grounds with ease. Yet despite these incredible adaptations, there are changes unfolding
in their habitats too rapidly for sea lions to handle. As climate change warms the oceans,
certain toxic algae species thrive. This algae is harmless to
the fish who eat it, but for the sea lions which
ingest those fish, the algae’s domoic acid can trigger
seizures and brain damage. Changing ocean conditions keep
this algae blooming year round, causing more and more sea lions
to wash up on beaches. This tragic discovery is just one
of the many ways the health of aquatic animal
communities can help us better understand Earth’s oceans. These red flags help us take action to protect ourselves and other
maritime mammals. And the more we can learn about the
changing ocean that sea lions inhabit, the better equipped we’ll be to help
these clever creatures thrive.
