Shark Gordon takes us to an underwater mountain top in Mexico’s Sea of Cortez for the annual school reunion of one of the most bizarre looking sharks in the sea—the Scalloped Hammerhead.

Forty miles (64 km) from the Mexican seaport of La Paz is El Bajo, an underwater seamount where scientists first discovered these Hammerheads in large schools.

The sharks gather for about three months while water temperatures are cool, but as presenter Ian Gordon finds out, the ferocity of local storms can make for poor water visibility and difficult diving conditions.

Local marine biology expert and dive guide Rocio Lozano explains how the numbers have varied hugely over the past 10 years, but there can be hundreds of Hammerheads at this amazing gathering.

Anchored nightly at the island of Espiritu Santo, in case a storm hits, the crew makes the two-hour trip to El Bajo.

On the way Ian takes a playful dive with some inquisitive Californian sea lions.

Charts and navigational aids pinpoint the spot. Straight below Ian shows us where El Bajo drops down 2000 ft (615 metres).

But there are no hammerheads. Visibility is poor and Ian’s scuba bubbles may be scaring the sharks.

He dons a specialist rebreather kit, which removes the CO2 from his breath and replaces it with fresh oxygen, releasing fewer bubbles. The dangerous blend of gases used in the system means there’s a lot more potential for disaster. Ian and the crew have incorporated his communications mask into this technology. Diving doesn’t get more complicated than this!

An Olive Ridley sea turtle appears to be undisturbed by Ian and then he spots the Hammerheads. But at 146 ft (45 metres) the 40 animals in the school are too deep for Ian and cameraman Mike Bhana to get close to. The rebreather equipment limits them to no deeper than 117 ft (36 metres) and poor visibility has them rethinking their strategy.

Then El Dorito, a renowned local electrical storm, which translated means “little bull’’, rages in shaking up the murky sea some more.

The crew decides to come back in autumn when the water is cooler and the sharks come up to a shallower depth.

Meantime, Ian heads to Hawaii’s Coconut Island to check out the latest scientific theory that Hammerheads may navigate their way to El Bajo via an electromagnetic sixth sense. Here Steve Cordura from the Hawai’i Institute of Marine Biology has been experimenting with baby Hammerheads using electric currents to create tiny magnetic fields that attract the sharks.

It’s autumn back in La Paz. Conditions are better and Ian is hoping for 60ft (18.4 metres) water visibility.

But El Bajo is a popular dive site—the dive boats gather and Hammerheads are naturally shy…..still no Hammerheads.

Nitrogen build-up in his blood means Ian can’t dive anymore today, so Rocio and cameraman Adam Jones take over the hunt. Just Ian’s luck! They come across a large school. Growing up to 13ft (4 metres) long, Scalloped Hammerheads are big enough to be nasty, but unlikely to attack unless provoked.

Finally Ian gets his chance—a school of 30 to 40 sharks where the females outnumber the males by about six to one, probably for mating reasons. Ian detects the “love bites” to prove it!

Finally he has witnessed El Bajo’s legendary Hammerhead school. He celebrates with his Mexican mates.

Statistics suggest there’s been a massive population decline and this concerns Ian greatly.

However, efforts are being made to conserve stocks. Ian hopes he can repeat this unforgettable experience in years to come.