Pizza Sharks

Richard has just arrived on board with a huge grin. “I got him!” he says. It’s a much different demeanor than yesterday, when he and Mike were incredibly frustrated at the “one that got away.” This time it’s not sharks but manta rays, though Richard says, “Rays are just sharks squished out and flattened like a pizza.”

One of the cool aspects of the Expedition Shark research is that they grab opportunities that arise to tag new species or ask new questions about the ones that they have been working with for years. When we drift fished to catch silvertips the thought was; why not try to catch them, too? They tried to catch the tiger shark when they spotted it, and they tried to catch grey reef sharks with a “claw.” Sometimes it works, and sometimes it doesn’t. After some frustration, Richard has now worked out a new technique to tag manta rays, and gather data on them as well as the whitetip and grey reef sharks.

“We are using technology straight out of a spy movie. We’re using radio tags and spy cams to look at what these animals are doing in real time,” says Richard.

Every morning since we arrived, divers have deployed a reefcam at Raging Horn, and retrieved it in the afternoon. The reefcam sits inside a watertight cylinder, and gives the scientists eyes into a world undersea. “Most of the shark research investigations put bait into the water. It’s based on observing the sharks after feeding them, which changes their behavior.” Collecting data on their movements and observing their real-time behavior undersea is shedding new insight into the world of these oceanic predators.

“Things we learned decades ago on land, we only have the foggiest idea about for the ocean, and about the largest predators on earth,” says Sanjayan. “It’s just astonishing. I’m a conservation biologist who has worked almost exclusively on land. And being part of this expedition really turned my worldview to understand that all the work that I do is really dwarfed by both the challenges of working in the ocean and the need for conserving the ocean.”

They set the reefcam at a “cleaning station,” where cleaner wrasse fish hang out and wait for marine organisms, including sharks, to show up for a parasite cleaning.  “Fish line up like a carwash,” says Dean Miller, who has worked with Richard on and off for the last eight years as Richard’s research assistant and videographer. “You see fish that would otherwise prey on each other, hold off. It’s like a no-go zone.”

Scientists have known that rays and sharks use cleaning stations for some time, but Richard wanted to find out how many different shark species are using them. Using a reefcam, they can find out. Cleaning stations are typically found where currents pass through, because the fish or sharks or rays can hover on the current while being cleaned. Sometimes the cleaning stations are near a geographically distinct feature. This particular cleaning station lies at 100 feet, across a channel where a strong current runs. Sea fans and soft corals abound here.

A spotted moray —much smaller and more colorful than the giant moray from the other day — makes its home in a crevice nearby. Near the cleaning station it looks like a giant graveyard of bones, broken off branches of once living coral, probably victims of a past coral bleaching event or perhaps a cyclone.

Coral bleaching happens when hot ocean temperatures cause algae that live in symbiosis with the corals to abandon ship. The coral polyps have a symbiotic relationship with zooxanthellae algae, and if the algae leave for too long, the corals die. When temperatures cool back down, the algae re-colonize and the reef can recover, but it takes time. Global warming has increased ocean temperatures around the world, and coral bleaching has affected many reefs worldwide, especially ones at shallower depths because shallow water heats up more quickly.

Dean gets the job of scanning eight or nine hours of reefcam video footage every night looking for interesting footage. “We didn’t know how many different species of sharks use the cleaning station,” he says. “On this trip we’ve seen manta rays, whitetips, silvertips, grey reef sharks, scalloped hammerhead, and a large unidentified species that was over 10 feet long.” He has also seen several interesting behaviors.

“We have seen stalling, which is when the shark uses the current to actually stop in the water to allow the cleaner wrasse to come up and service them. We’ve seen sharks moving out of the way for larger sharks of different and the same species. Yesterday I saw four scalloped hammerheads swimming side by side with the school of chevron barracuda.”

About halfway through our trip, Dean started seeing a lot of manta rays on the footage, and some of the divers spotted them when they’d put down and pick up the reef cam. So Richard thought, why not try to put pinger ID tags on them too? They hatched up a plan to use a speargun to shoot a pinger onto a manta’s wing.

So for the past three days, they have tried to do just that. The first day, Richard thought he had one in the bag. He shot the pinger from the speargun, but it whizzed past. “I’ve never had something where I was so sure I’ve had it, and then it got away.” He came back on board frustrated. Several other diver teams then tried, but didn’t see manta rays when they arrived at the cleaning station. But then, success! Richard, one; Mike, zero.

This morning, the crew tried to tag more mantas in teams of two, leaving every 15 minutes. Mike explains his shift. “We had all this crap with us—the reefcam, the data logger, the spear and cutters and zip strips, and down we go. We had a lot to do. Set the reefcam. Set the data logger. And we had to tag a manta ray in 20 minutes. That’s all the time you’ve got at that depth. So we got down there and I still had this crap in my hand and there was the manta ray,” Mike explains. “It was a beautiful situation where the manta was being cleaned. It was going in circles. He went around once and we couldn’t get him. He went in a second circle and pop, he’s done.”

The researchers have now completed a network of 32 receiving stations around Osprey Reef that detect the pingers. “Now we’ve got two manta rays in the grid,” Mike says, thrilled. Any time these mantas get within 300 feet of any of the receivers, their presence will get recorded. “This was an opportunity to put a really important tag on a very important species in very important experiment.” Richard, one; Mike, one; sharks and mantas, 62 tags.

Images: JR and Richard plan tagging strategy; Moray eel in the coral; Richard with spear gun for attaching pingers to manta rays.

Photos: Cat Gennaro/DCL

Comments

[Susan See]

Goodness, I don't know how in the world you keep such a busy day straight in yer head and then to write it down later! Great stuff Wndee.

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