Journey of Life - Seas of Life 10
Steve travels back 3.8 billion years to when life began. Journeying round the oceans, he explores life's first laboratory and discovers how the incredible variety of sea creatures arose, from the first microbes to hagfish and dolphins.
Sharks like this Caribbean reef shark can hear a commotion from at least a mile away. They have excellent hearing, but instead of having ear flaps on the outside like we do, a tiny duct carries sound waves into their inner ear.
Next comes the sense of smell. Blood and fish oil can be detected from 400 meters away. So this box of fish bits should generate some interest.
Just a single drop of blood in 25 million drops of water is enough to turn a shark's head. But to pinpoint exactly where the smell is coming from, it has to zigzag to pick up the trail. At a hundred meters, now the shark knows where I am, thanks to a sense humans don't have at all. It can't see me, but it can feel me through the pressure waves that I'm creating in the water. These waves are picked up by the lateral line--detectors that run down its body from head to tail. It's a kind of extrasensory perception all fish have.
"And it's only now at around ten meters that the sharks can actually see me and I see them. In daylight, their vision is about as good as mine. And now they are checking me out with those big eyes."
The structure of the eye suggests sharks may be far-sighted. They see better at distance than close up. But once they get this close another sense kicks in, they can detect electricity. Tiny receptors on the snout can register as little as half a billionth of a volt. That's the electric field around a live fish's body or in this case in our metal feeding pole. I'll leave this bit to the professionals.
"Wow, easy, gent."
In the final seconds of attack, the shark goes in blind to protect its eyes, closing them just before it bites.
"In clear blue water like this, thankfully the sharks can actually see what I am, otherwise they may have to use their other senses. Namely touch and taste and it's all done with the mouth. And it is this combination of sensory systems that makes the shark such an effective hi-tech predator."
You might think that such sophisticated animals would out-compete everything else in the sea. But the journey of life has never been straightforward. Several times over the millennia, meteors have shattered the world order and sparked mass extinctions. But from these extinctions, new opportunities and new creatures arose. |
