Whale Sharks, A-bombs and the Hubble Space Telescope

Pregnant whale shark female at Darwin Island in the Galapagos. In 2014, members of the Galapagos Whale Shark Project reported sightings of 27 whale sharks, all females, all but one pregnant around Darwin Island in the Galapagos archipelago.

Photograph © 2011 Josef Litt

We know very little about the biggest bony fish in the oceans, the whale shark.

Whale sharks are the world’s most giant fish, growing up to twenty metres in length – more than a bowling lane and almost as long as a passenger train coach. We don’t know how fast they grow and what is their maximum age. The best estimates are that the big ones may be more than one hundred years old.

The Atomic Bomb Method

Scientists determine the age of sharks by counting growth rings in their vertebrae. This method seems to provide reliable results for younger animals. However, one needs an atomic bomb to make the reading more precise in case of the older sharks. The nuclear tests performed in the 1950s and 1960s increased the amount of radiocarbon in the atmosphere. The radioactive material entered the oceans and imprinted a timestamp in the whale sharks vertebrae. Today, this timestamp helps to establish the age of older individuals.

Juvenile whale shark. We encountered this juvenile on top of the shallow platform underneath the Darwin Island in the Galapagos.

Photograph © 2011 Josef Litt

The Hubble Space Telescope Method

To paraphrase Douglas Adams in the Hitchhiker’s Guide to the Galaxy: ‘Whale sharks are big. Really big. You just won’t believe how vastly hugely mind-bogglingly big they are.’

From that slightly facetious perspective, it is no surprise that the scientists use the Hubble Space Telescope to identify individual whale sharks. The spots behind their gills form an ornament as unique as a fingerprint. Jason Holmberg, the co-founder of WildMe.org, adapted an algorithm used by NASA with the telescope to recognise and compare the patterns. Thanks to that anybody who photographed a whale shark anywhere in the world can upload their images to the Wildbook for Whale Sharks. Almost 8,000 people identified more than 10,000 whale sharks during close to 60,000 sightings. The data give scientists information about the distribution and movement of the gentle giants, hopefully leading to their adequate protection.

Photograph © 2011 Josef Litt

The Value of a Whale Shark

Since 2016, IUCN describes the whale sharks on its Red List as Endangered. The reason is the demand for shark fins in Asia and the nature of whale shark meat, often referred to as ‘tofu shark’. Infuriatingly, despite their size, they also end up as bycatch. Since early 2017, whale sharks enjoy protection as migratory species in more than 125 countries. A number originating from research in 2004 estimates their value to tourism at over USD 47.5 million a year – an amount that is indisputably higher today. Hopefully, governments will realise the species’ importance and enforce the protection they committed to.

Photograph © 2016 Josef Litt

The Whale Sharks’ Birthplace

Members of the Galapagos Whale Shark Project in 2014 reported sightings of 27 whale sharks, all females, all but one pregnant around Darwin Island in the Galapagos archipelago – this seems to be a typical situation confirmed by tourists’ observations. Jonathan R. Green, the leader of the Galapagos Whale Shark Project, explores a hypothesis that the deep sea surrounding Darwin Island serves as a breeding ground for whale sharks. However, nobody has ever seen a whale shark to give birth or breed.

I heard a fisherman speculate about the reason why the whale shark males avoid the Galápagos. Their little cousins, the silky sharks, frequent the islands waters in search of food. Remoras belong to their favourite staple. An attacked remora would hide among the whale sharks’ claspers to protect itself. The ferocious silky shark will hardly differentiate between a remora and a clasper. The poor male whale sharks are afraid that they may get hurt in such a sensitive place, so they avoid Galápagos at all cost. I wonder whether there is a scientific base to this speculation.

Photograph Simon Pierce https://www.simonjpierce.com.

Ending with a Hairy Story

Whale sharks were never seen feeding at Galapagos, which gives the following story* a whiff of a fairy tale.

‘As with any other animal on the Galápagos, and it should be a good practice anywhere in the world, touching whale sharks is strictly forbidden. This was not a well-observed custom some time ago, perhaps ten or twenty years back when, according to a local legend, one of the naturalist guides nicknamed Zorro Plateado, or Silver Fox, used to ride the whale sharks holding on to their dorsal fin. As if this was not enough, he supposedly dragged himself from the dorsal fin and then plunged headfirst over the animal’s upper lip into its gaping mouth. Disappearing into the poor whale shark’s maw, he was gushed out after a moment in a shroud of his bubbles, in slight disarray, but unharmed. The animal seemed to be unperturbed, it turned slowly and swam away. The diver’s equipment could have easily injured the whale shark, and I indeed believe that such acts would not be tolerated today.’

I was pleased to be contacted by the family of Zorro Plateado in reaction to this story. I welcome first-hand information rather than an unconfirmed narration by somebody else. Zorro declines the story featuring him and a whale shark as untrue. The truth is that he was honoured with a plaque from the Charles Darwin Foundation for his constant efforts in teaching the children the importance of conservation. He also plays an important part in CDF’s Shark Ambassador Program.

I hope I will have a chance to meet Zorro in person soon.

*A spoiler citation from Litt, Josef. GALÁPAGOS. Mostly Underwater Books. The United Kingdom, 2018.
A similar story was also mentioned in Bantin, John. Amazing Diving Stories. United Kingdom: John Wiley & Sons Ltd, 2012.

Photograph © 2017 Ivan Jiskra