Shark Week: How to Prep Great Hammerheads for an Underwater Ultrasound

Mandi Bierly
Deputy Editor, Yahoo Entertainment

Shark Week kicks off tonight on Discovery, and while yes, great whites are usually the star (whether or not they’re racing Michael Phelps), another species steps into the spotlight.

Great Hammerhead Invasion, premiering at 10 p.m., explores why great hammerheads, which can grow up to 20 feet long and are endangered globally, congregate each year off Bimini, the westernmost island of the Bahamas. Tristan Guttridge and his team at the Bimini Shark Lab have a theory: Many of them appear to be pregnant females. If the team can perform an ultrasound and confirm it, it could mean that Bimini is an important prenatal feeding ground for great hammerheads, who binge on stingrays before heading off to their pupping grounds.

As you see in the clip above, Guttridge’s initial plan is to perform an underwater ultrasound, which requires working with the sharks for days in advance to acclimate them to touch. “Great hammerheads in particular do really poorly on capture. They’re very sensitive. They’re kinda like a Ferrari — they just have this incredible explosive power and sensitive chassis. So if they spend very long on a hook, they use up a lot of energy and they can’t seem to replenish their oxygen stores and they just crash, and a lot of them will die,” Guttridge tells Yahoo TV. “So that was playing on my mind when I was trying to think, ‘Well, how are we going to determine if these animals are pregnant or not?’ We had a unique situation where hammers were coming in, in shallow water, and they’re habituated to humans. Some of these larger migratory sharks are quite spooked around people, but because they’re being provisioned at this site, they spend a little bit more time with humans and they’re easier to access.”

The specially designed handheld underwater ultrasound machine worked, however, he couldn’t get enough contact with the hammers for a clear reading before it flooded. So the team moved on to Plan B, which was capturing a shark for a very short period of time to perform the ultrasound boatside. “It was a first for me and a first for anyone in Bimini to ultrasound a great hammerhead. I don’t think anyone has done it anywhere in the world,” Guttridge says. “As the technology’s becoming handheld, it’s just opening up a whole host of options, which is really cool, especially because female hammerheads that are gravid are a really important animal to protect, more than other individuals within the population. Knowing where and when those particular individuals are going, and where they’re pupping, is crucial data for us.”

That’s the next step, Guttridge says, determining where the great hammerheads go when they leave Bimini (which is likely to Florida, to fatten up on blacktip sharks, and South Carolina). “Although we have an inkling that’s where they are pupping, we don’t really know. And whether the same females are returning to the same grounds each year, or every couple of years, we’re not sure as well, and that clearly has important implications for managing their populations,” Guttridge says. “They’re one of the most charismatic and enigmatic species out there. You often only come across maybe one great hammerhead, and in Bimini, we’re seeing between 20 and 30 different animals each year turning up and sticking around the island for a good three to four months. So it’s crazy not to explore the reasons why they’re in Bimini and also use the hammers in Bimini as a model to learn more about hammerhead biology in general.”

Shark Week kicks off July 23 at 7 p.m. on Discovery and continues through July 30.

Read more from Yahoo TV:
Shark Week Sneak Peeks: Phelps vs. Shark, and Shark vs. Croc

Michael Phelps on His Shark Week ‘Race’ With a Great White
Shark Week’s ‘Return to the Isle of Jaws’ Has a Major Discovery
Shark Week: Charlize Theron, Tony Hale to Guest on ‘Shark After Dark’