A crowd of tourists gather at the stern of the ship to watch Mexican shark scientist, Mauricio Hoyos swim across 80 metres of the Pacific Ocean to his rudimentary camp on the shore of Isla Guadelupe.  Earlier that day, we had all watched a four metre, 700 kilo great white shark effortlessly scissoring a  huge tuna in half with its razor sharp teeth next to the boat. Looking on from the protection of a submerged metal cage is a bit different to Mauricio’s surface swim with only a waterproof computer case and a bag of clothes for protection. He did make it safely.

 

It not only tuna that are on the menu.  We can see a young male elephant seal on the beach, with a fresh wound and bite marks all around its neck.  ‘His head must have been right inside the shark’s mouth, that’s one lucky elephant seal,’ says Patric, CEO of SharkDiver.com. This is the first documented attack by white sharks on elephant seals at the island, and supports Mauricio’s research results that these sharks are feeding on both tuna and pinnipeds. Three species of seal inhabit the island; elephant seals, Californian sea lions and Guadelupe fur seals, but during shark season, their numbers are swollen by up to 800 human visitors.

 

Shark tourists, photographers and scientists alike are drawn to this barren volcanic island, 160 miles off the Pacific coast of Mexico. Male and female sharks gather here in the clear blue waters between August and January. Mauricio’s goal is to find out exactly what these top ocean predators are doing at the island.   ‘I have to get the shark to swallow an internal transmitter equipped with three small hooks by disguising it inside a tempting fishy package.  It usually disappears in one gulp, whole,’ he explains grinning, ‘It has always been a dream of mine to work with these animals, ever since I was a little kid and here I am.’

 

During the roughly 3 weeks that the transmitter stays inside the shark, sensors measure the shark’s stomach temperature so we can learn what the animal is eating.  A lower temperature means that the shark is dining on fish, while a higher temperature shows up when the animal has to digest a muscled, warm bodied animal like a seal. The probe is ejected naturally when the shark turns its stomach inside out.  The animal doesn’t merely vomit up the contents, but everts its entire stomach through its mouth. All the indigestible hard parts that have stuck there like seal bones, and the odd transmitter, are ejected, then the shark takes it all back inside.

 

Far from their undeserved and terrible reputation as aggressive and mindless killers portrayed in movies since Jaws, the 30 year old scientist is recording complex behaviour amongst his study animals.  ‘White sharks have to be pretty cautious when they meet another shark.  Both are equipped with a fearsome armoury of teeth that could cause the other a lot of damage,’ points out Mauricio while showing me an underwater video. We watch as they start swimming along, side by side, eyeing each other up.  This helps them work out which is the bigger, and the smaller animal usually gives way.  But things do sometimes get out of hand.  Mauricio has seen a lot of scarring on both males and females on the snout, eyes and around the gills. Some of these are due to tussles that establish where in the pecking order an individual lies. ‘I saw a small male come in and take a bait, but he did not see the large female nearby who also was aiming for it.  Seconds later, the male was being thrashed between her jaws and suffered terrible wounds to his gill slits.  These animals have tremendous powers of healing, I can see near fatal wounds like that one year, perfectly healed the next when the same shark returns.’

 

Sexual scarring on females around the dorsal and pectoral fins is caused by an amorous male, grabbing her in his jaws to hold her still for long enough so that he can mount her.  Both types of scarring make it easier to visually identify individuals and there is now a database of photographs that shows over 90 named individual animals who return to the island each year.  Mauricio will be  spending a 24 hour period out on the water in a small boat later this month, listening to his hydrophones,(underwater microphones) as his tagged shark emits pinging sounds that reveal where it is swimming, if he can get the same shark to swallow an internal transmitter, then he will know what it is eating too.  It sounds pretty basic to be finding out what an animal is eating, but much of the lives of these majestic top ocean predators remain a mystery to us.  We do not know where they breed, or give birth, how many there are in the oceans, how big they get, how long they live or very much about their behaviour, all very important if we are to be able to protect the species.

 

 

Barb and her team have tagged 65 animals since 2004 in their coastal island haunts off California, all seal colonies like Isla Guadelupe and what they have found is remarkable but still unexplained.  Each winter the sharks leave and head out into the Pacific Ocean to a spot about half way between Hawaii and California.  And there they hang out for up to six months.  The team dubbed the spot - the white shark café, at first assuming that it must be food that was drawing the sharks together. But it is the oceanic equivalent of a desert, a featureless aquatic wasteland with no food.  So if it is not a café, then sex must be involved, they reasoned.  ‘Adult males and females were showing up,’ says Block, ‘But then adolescents arrived too, which does make us wonder what’s going on.’  Whatever the animals are gathering there for, and Barb hopes to have the answer soon as their concentration there could make them vulnerable to fishermen who set longlines for tuna.

 

White shark tourism at Guadelupe is important in that ordinary people come to see these magnificent animals in the wild and end up as great ambassadors for the future protection of the much misunderstood great white.