0:00:04 > 0:00:08On Deadly 60 I've had loads of incredible animal encounters.
0:00:08 > 0:00:11Here's just one of my many favourites.
0:00:17 > 0:00:21We're skimming over chilly South Australian seas.
0:00:21 > 0:00:24Around about here.
0:00:24 > 0:00:27Although my crew's about to take off at the moment!
0:00:27 > 0:00:29Stick with it, guys.
0:00:29 > 0:00:33Today's animal is deadly because it's quick.
0:00:33 > 0:00:36You're looking at the fastest fish in the seas.
0:00:36 > 0:00:39They're all submarine speedsters,
0:00:39 > 0:00:42but the fish I'm after is turbo-charged,
0:00:42 > 0:00:44clocking up speeds of over 70km an hour.
0:00:44 > 0:00:48Ladies and gentlemen, I give you...
0:00:48 > 0:00:49the tuna!
0:00:49 > 0:00:53But first, a bit of Deadly 60 science.
0:00:53 > 0:00:57The big enemy of anything trying to travel fast in water is drag.
0:00:57 > 0:01:00That is the force of the water holding you back
0:01:00 > 0:01:02as you try and move forwards.
0:01:02 > 0:01:05To get around that you have to be streamlined.
0:01:05 > 0:01:09In the air that's aerodynamic, in the water hydrodynamic.
0:01:09 > 0:01:12The tuna is just about the most perfect example
0:01:12 > 0:01:14of a hydrodynamic fish.
0:01:14 > 0:01:17I, on the other hand, am not that streamlined.
0:01:17 > 0:01:21So, theoretically, if I was to get in there and try and travel fast,
0:01:21 > 0:01:23I should be hammered by drag.
0:01:24 > 0:01:30So, we already know that tuna can travel up to around 70km an hour,
0:01:30 > 0:01:33which equates to about 38 knots.
0:01:34 > 0:01:36OK, Captain, hit it!
0:01:41 > 0:01:44You can see as we start to build up speed,
0:01:44 > 0:01:48automatically the water's pushing back against me
0:01:48 > 0:01:51and I'm really struggling to hold on.
0:01:53 > 0:01:56I'm actually already losing my trunks!
0:01:56 > 0:01:59What speed are we at, boys?
0:01:59 > 0:02:02That's 4.7 knots, Steve.
0:02:02 > 0:02:07Well, I've still got hold of the rope but I've only just got...
0:02:07 > 0:02:09How fast now?
0:02:09 > 0:02:10What's that?
0:02:10 > 0:02:116.8.
0:02:11 > 0:02:12Aaah!
0:02:14 > 0:02:17- I've lost my trunks! - Lost his trunks!
0:02:18 > 0:02:23This is not good. I hope you can't see my bottom!
0:02:24 > 0:02:28OK, so we're now going about a tenth of the speed
0:02:28 > 0:02:31that a tuna can go full whack.
0:02:31 > 0:02:34It's almost pulling my arms out my sockets!
0:02:34 > 0:02:37And I'm absolutely naked!
0:02:37 > 0:02:38Ha-ha!
0:02:38 > 0:02:40How fast's that, Mark?
0:02:40 > 0:02:42- Seven knots.- Seven.
0:02:42 > 0:02:45No! That's rubbish!
0:02:45 > 0:02:48- Switch faster.- Aah!
0:02:48 > 0:02:49He's gone.
0:02:49 > 0:02:51He's gone, Mark, he's gone.
0:02:51 > 0:02:52What's that?
0:02:53 > 0:02:54See you, Steve!
0:02:54 > 0:02:56Bye, Steve!
0:02:56 > 0:02:57- Bye!- Bye!
0:02:57 > 0:03:00He's got a nice bum though, hasn't he?!
0:03:00 > 0:03:02Yeah, I noticed. He must work out.
0:03:03 > 0:03:07What was our final speed when he let go, Mark?
0:03:07 > 0:03:088.5.
0:03:08 > 0:03:118.5, oh, he did quite well.
0:03:11 > 0:03:13Not bad for a beginner.
0:03:13 > 0:03:17I think that pretty much proves that unless you're streamlined
0:03:17 > 0:03:20you ain't going nowhere in the water.
0:03:20 > 0:03:24And it also proves why fish don't wear swimming costumes!
0:03:24 > 0:03:27You better not film this when I try and get out the water.
0:03:30 > 0:03:34So, so far we've proved that I can't swim.
0:03:34 > 0:03:36As well as a tuna!
0:03:37 > 0:03:39But I can't dry off yet
0:03:39 > 0:03:43cos I still wanna get in the water with these amazing creatures.
0:03:46 > 0:03:51Growing up it never really occurred to me that the fish in these tins
0:03:51 > 0:03:55are some of the most special and some of the fastest in the seas.
0:03:55 > 0:04:00Unfortunately they're prized as food which means they're becoming rare.
0:04:00 > 0:04:04Fishermen, attempting to make sure they don't become extinct,
0:04:04 > 0:04:07have started keeping tuna in these big nets,
0:04:07 > 0:04:10giving me a unique opportunity to get close to them.
0:04:20 > 0:04:24There are lots of different types of tuna.
0:04:24 > 0:04:28The ones swimming round in here are about as big as me,
0:04:28 > 0:04:31but the biggest ever was heavier than a horse!
0:04:31 > 0:04:35This is extraordinary! There's hundreds of them.
0:04:38 > 0:04:42Each one of these tuna weighs almost as much as me
0:04:42 > 0:04:45but they swim effortlessly.
0:04:45 > 0:04:46Just gliding past me.
0:04:46 > 0:04:49They're barely swimming, look!
0:04:50 > 0:04:52I feel like fish food!
0:04:52 > 0:04:53Look at that!
0:04:59 > 0:05:02Being up close to them under water
0:05:02 > 0:05:05makes it easy to see why they're deadly predators.
0:05:05 > 0:05:11They are the perfect shape, nothing sticks up off it to slow them down.
0:05:11 > 0:05:14So they move with just a flick of their tail.
0:05:14 > 0:05:16Awesome! Ha-ha!
0:05:17 > 0:05:22Luckily, tuna fish eat small fish like sardines.
0:05:22 > 0:05:26If I was a sardine now, I'd last about a second.
0:05:27 > 0:05:31Tuna accelerate faster than a sports car.
0:05:31 > 0:05:35And they've got the best eyesight of any bony fish.
0:05:35 > 0:05:39So, if there are sardines around, things are gonna get pretty hectic.
0:05:46 > 0:05:51The tuna is as close to a torpedo as you'll find in the animal kingdom.
0:05:51 > 0:05:52Look at them go!
0:05:54 > 0:05:58They'll pick out the stragglers on the outside of the shoal.
0:05:58 > 0:06:03If a sardine loses his buddies for even a second, WHAM! Munched.
0:06:15 > 0:06:16Great stuff!
0:06:16 > 0:06:20I feel like I've been in a subaqua version of Top Gear!
0:06:20 > 0:06:23The tuna is kind of like the Porsche of the seas.
0:06:23 > 0:06:27They accelerate faster and can be almost as big
0:06:27 > 0:06:29and they can even cost more.
0:06:29 > 0:06:32And they're definitely going on my Deadly 60!
0:06:36 > 0:06:40The world's most hydrodynamic fish.
0:06:40 > 0:06:43A streamlined super speedster of the sea,
0:06:43 > 0:06:46the tuna is on the Deadly 60.