PICTURE IT – you’re cruising through the blue waters of the Galapagos, after spending 36 hours on a tiny boat to reach the remote Darwin Arch. And now before you is what you came to see, an enormous shape emerging from the deep – an adult whale shark.
At well over 10m long, this female must surely be the biggest creature to have shared the water with you.
Or perhaps not, you think, as another “mega-mama” cruises into view, this one even bigger than the first.
As you brace yourself against the current, a diver approaches the shark clutching a large metal briefcase, like some kind of futuristic underwater commuter.
You blink. The diver zooms effortlessly through the water alongside the shark. Looking more closely to see how he’s able to move so quickly, you notice that he is propelled by a jet-pack.
It might come across as something from a sci-fi movie, but had you been in the Galapagos last year you might have seen just this sight. For two weeks in September, a team of experts were using cutting-edge technology to find out more about whale-shark reproduction.
Until this point, we knew pretty much nothing about how whale sharks breed. No-one has ever seen a whale shark give birth. Ever. And only one pregnant female has been physically examined.
Incredibly, she had more than 300 eggs and tiny pups inside her – twice as many as any other shark species.
Since then – and that was in 1995 – nothing. Researchers have had lots of questions and few answers.
Where could they find the clues to solve this mystery? The Galapagos promised to hold the key. It’s one of the few places in the world where adult female whale sharks nine to 14m long are regularly seen.
Jonathan R Green, founder of the Galapagos Whale Shark Project and leader of the expedition, thought the presence of these females presented an opportunity to learn more. Could they solve the mystery?
The expedition scientists dived the same site three times a day, yet each day was different, according to Dr Simon J Pierce, co-founder of the Marine Megafauna Foundation. “Conditions are really variable, so you never know quite what you’re going to get,” he told me.
“One day you can have 26° blue water with stunning visibility, no current and sharks everywhere. The next, the temperature could have dropped to 21°, with a current so strong that you have to hide behind rocks for shelter. I’ve watched hammerheads swim past me sideways because of the current!”
Jet-propelled Dr Rui Matsumoto applies the whale-shark ultrasound.
What’s more, there are a lot of sharks. Scalloped hammerheads, silky, Galapagos and, of course, whale sharks.
Being surrounded by so many sharks is refreshing for Pierce because, elsewhere in the world, sharks have been overfished so much that it’s rare to see one at all.
Around Darwin Arch and neighbouring Wolf Island, the waters have an average of 17.5 tonnes of fish per hectare: “It’s the highest biomass of reef fish recorded anywhere, and most of these fish are sharks,” he says.
“You’ll see enormous schools of fish coming through, especially jack and huge yellowfin tuna which, for some reason, all the fish are terrified of. I’ve never done a dive there and not seen at least one hammerhead.”
There are several reasons for the Galapagos being so “sharktastic”, as Pierce puts it. Upwellings of deepwater plankton make it rich in food for plankton-feeders (although whale sharks don’t seem to be feeding there) and the fish, in turn, attract the sharks that come to feed on them.
The seafloor around Darwin is made up of magnetic rings from previous volcanic eruptions, and these align either
with the Earth’s current polarity or its opposite. This is because minerals within volcanic lava align themselves with the Earth’s magnetic field, which reverses itself roughly every 500,000 years.
They also “record” irregularities in this magnetic field, so each ring has its own unique magnetic fingerprint that marine animals can use for navigation.
When whale sharks come to the Galapagos they are, essentially, stopping for directions, or calibrating their GPS.