Coming up on Jonathan Bird's Blue World,
a fish that sticks to sharks!
Hi, I'm Jonathan Bird, and welcome to my world!
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Everyone knows that I love sharks, and I have spent a lot of time watching them and filming
them. You may have noticed that sharks very often have hitch-hikers: a peculiar fish hanging
on for a free ride.
24 hours a day, sharks often seem to be plagued by many of these freeloaders.
Being a big tough Tiger shark doesn't make you immune to the attention of these fish.
The bigger the shark, the bigger the freeloader!
They're called remoras, and they don't limit their attention to sharks. Any animal from
the massive whale shark to dolphins, whales and even sea turtles may have a remora or
two attached.
Although at first these fish may seem more like parasites, they actually perform an important
function. The remora gets some of its meals by picking real parasites from its host. They
actually help keep their host clean and healthy.
Remoras also take advantage of a shark's messy eating habits, feeding on scraps which
escape the shark's jaws.
The remora attaches to its host using a strange-looking sucker on the top of its head. This is actually
a modified dorsal fin, changed over millions of years of evolution to form a suction cup.
Got 'em!!
Here is a remora. On the top of its head is a suction cup. You can see all away around
little flap of skin that allows it to form a suction cup to stick on to other fish. And
on the suction cup it has little ribs that are smooth in one direction and sandpapery
rough in the other direction. This is actually their dorsal fin, which has evolved to become
the suction cup. So this is the top--even though it looks upside down right now--that's
the top of the remora.
So this underneath is the belly. That's the belly. Now watch this. If I let it stick
on my hand it will grab on. Even when I'm out of the water can hold its own weight.
So now we've done enough I think we'll let this little guy go. Actually we don't
know if it's a guy or a girl but we're going to let it go. First I'm going to un-stick
it. Here we go. Ready? All right! Swim! Be free!
Remoras may perform an important role for their host, but this is not to say that they
don't bother them.
I have traveled to the island of Yap to try a little experiment with sharks and remoras.
Right down below the boat is a school of gray reef sharks and some of those sharks have
remoras on them. We're going to feed the sharks and get them really excited, and wait till
you see what happens!
I drop down below the waves to join the sharks which are already swarming around the reef,
looking for some hidden fish.
The sharks get really excited when we start feeding them. As they bump against each other
and compete for food, many of their remoras get knocked off.
After the excitement dies down, these remoras find themselves homeless...swimming around
without a host. Now they need to get back on a shark, but this is not as easy as you
might think!
This remora is stealthily approaching a shark, but notice how it's careful not to touch the
shark. If the shark takes off before the remora sticks on, the remora can't keep up.
Here's what happens when a shark can feel the remora. It turns away and the remora can't
get a grip. This is how we know that the sharks don't really like the remoras. Given the chance,
they take off will before allowing a remora to attach. Maybe they tickle?
Soon it tries again, this time with another shark. Getting a free ride is not as easy
as it looks!
I spend a few minutes filming the remoras. Fortunately, remoras don't find divers particularly
attractive, so I don't need to worry about dodging them. Maybe it's because I don't have
any parasites to clean. Maybe the scuba bubbles are too loud.
As I end my dive and head up to the boat, I am again amazed by the creatures of the
ocean. I have seen remoras a thousand times on dives all over the world and never given
them much thought. It turns out that they have a fascinating life and we have probably
only just scratched the surface in learning about them.
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