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  • 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.

Sunning themselves on rocks or waddling awkwardly across the beach,

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B2 US TED-Ed sea algae fish lens hunting

The lovable (and lethal) sea lion - Claire Simeone

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    高詩詩 posted on 2019/07/27
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