Blue Shark

0:00:02 > 0:00:06My name's Steve Backshall. Self-confessed shark-obsessed.

0:00:06 > 0:00:08This is Shark Bites.

0:00:10 > 0:00:13This time, we meet the ultimate aquatic athlete...

0:00:14 > 0:00:16..the blue shark.

0:00:16 > 0:00:20Living in the open ocean, they undertake mammoth migrations.

0:00:21 > 0:00:23Found in most oceans throughout the world, they're

0:00:23 > 0:00:27constantly on the move, travelling to annual breeding sites

0:00:27 > 0:00:29and in search of rich feeding grounds.

0:00:31 > 0:00:35In the Atlantic, they journey full circle between America and Europe,

0:00:35 > 0:00:40while a similar cycle in the Pacific clocks up 9,000km.

0:00:42 > 0:00:47So, how does this bolt of blue achieve such massive migrations?

0:00:47 > 0:00:51California's coast is the perfect place to see them on their travels.

0:00:56 > 0:00:59Curious and bold, blue sharks will take a pit stop break to

0:00:59 > 0:01:02investigate anything that could be food.

0:01:02 > 0:01:05And it doesn't take long for one to check me out.

0:01:05 > 0:01:10They have the most glorious blue shade to the skin.

0:01:10 > 0:01:13Got one just nudging my camera now. Look at that!

0:01:13 > 0:01:16He's right in my face!

0:01:16 > 0:01:18So inquisitive, so interested.

0:01:18 > 0:01:21Just sticking their noses in absolutely everything.

0:01:23 > 0:01:26Any predator has to have a good-sized brain.

0:01:26 > 0:01:29They have to have processing power to figure out problems,

0:01:29 > 0:01:31to figure out how to catch their prey.

0:01:31 > 0:01:33And you can see that that has developed a big

0:01:33 > 0:01:36personality in this shark.

0:01:36 > 0:01:40It really is just like... I don't know, a friendly dog.

0:01:40 > 0:01:42An inquisitive nature helps them find food -

0:01:42 > 0:01:46vital for keeping energy levels high during their voyage.

0:01:47 > 0:01:51But these athletes also have an ingenious bit of kit to keep them

0:01:51 > 0:01:53going the distance.

0:01:56 > 0:02:00Surprisingly, some sharks would sink if they stopped swimming.

0:02:00 > 0:02:03Unlike many fish who have an air-filled swim bladder that

0:02:03 > 0:02:07gives them buoyancy, sharks, including the blue, don't.

0:02:07 > 0:02:11Instead, they rely on their large liver.

0:02:11 > 0:02:15In some sharks, this can be up to a quarter of their body weight,

0:02:15 > 0:02:18and it's filled with oils which are lighter than water.

0:02:18 > 0:02:21This gives them a little bit more buoyancy,

0:02:21 > 0:02:24which means these athletes can keep going for longer.

0:02:26 > 0:02:29But it's not only using this lubricated liver that

0:02:29 > 0:02:31helps them keep travelling.

0:02:31 > 0:02:34Ocean currents act like a conveyor belt,

0:02:34 > 0:02:37so blue sharks hitch a ride on them,

0:02:37 > 0:02:40saving even more energy to cross the finish line on their

0:02:40 > 0:02:42marathon migration.

0:02:45 > 0:02:48The blue shark. With its sleek and streamlined body,

0:02:48 > 0:02:52armed with its very own buoyancy device and undertaking

0:02:52 > 0:02:57mammoth migrations, it is, without doubt, the ultimate aquatic athlete.