The second big catch of the day for shark biologist Neil Hammerschlag and his crew is another great hammerhead.
Her dorsal fin knifes through the surface of the emerald ocean, and then there’s a splash, a thrust and the decisive nod of that rectangular, prehistoric-looking head with shiny black eyes set wide on opposite ends, as if the shark is saying, “Behold me because you will never vanquish me.”
She’s reeled in to the stern of the boat, where four prone people clamp down on her thrashing body while others hold their feet so they don’t fall in. Hammerschlag inserts a water hose into her mouth, which acts as a pacifier. But he and his marine biology students must work quickly. Their goal is to collect blood and tissue samples, take measurements and attach an identification tag. Because the hammerhead is an endangered species and has a fragile and anxious constitution — the Nervous Nelly of the shark family — they keep her in the water rather than lift her onto the platform, and release her within five minutes.
“There she goes,” Hammerschlag said after jumping in the water to follow and observe the shark and make sure she has recovered. “They are sensitive to capture stress but she’s swimming hard, she’s OK.”
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A red blob sticks out of her jaws. It’s her stomach, which she regurgitated to clear its contents. While she wriggles around behind the boat, she swallows her stomach and resettles her digestive system — an ingenious anatomical skill humans could employ after junk food binges. The shark descends. She’s gone.
The hammerhead is one of three Hammerschlag and his team from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science will catch and release on a calm and steamy day three miles offshore. Their mission is to tag the sharks to further their illuminating research on one of the most fearsome, mysterious and threatened creatures of the sea.
Miamians share their territory with sharks yet harbor many misconceptions about them. Did you know there hasn’t been a shark attack in Biscayne Bay in 69 years? Man is not on their menu. The sharks among us tagged by Hammerschlag include downtown denizens who hang out near the Brickell seawall, swim up the Miami River, dodge cruise ships in Government Cut and explore the waters behind AmericanAirlines Arena and Museum Park.
“Miami is shark mecca,” said UM graduate student Shannon Moorhead.
Added fellow student Robbie Roemer: "They are closer than you think. There are no fences underwater."
About 100 million sharks are removed from oceans annually, and exploitation rates are exceeding their rebound ability. Among the 500 species, many populations are declining, including hammerheads, white tips, threshers and Atlantic makos, and 16 percent of species are threatened with extinction, Hammerschlag said.
“The planet is changing and the ocean won’t be the same tomorrow,” said Hammerschlag, who runs the Shark Research and Conservation Program at UM. “Sharks are suffering due to targeted fishing for their fins and meat, habitat degradation, climate change, pollution, plastics, urbanization, alterations in water quality and temperature.
“Sharks are at the top of the food chain, so they are the sentinels, the canaries in the coal mine. We’re trying to see how they are coping, how they adapt or not. What’s their immune status? How does body shape and movement change as they age? How often and how much do they reproduce? How can we make effective conservation decisions, such as adjusting fishing behavior to limit interaction with certain species?”
The sharks, lured by barracuda bait, are tagged using an applicator that injects a small metal clip under the dorsal fin. The numbered tag dangles behind “like an earring,” explains UM graduate student Elana Rusnak, who demonstrates on a stuffed toy shark named Sharkey who has been punctured many times but still has a toothy grin.
“Tagging doesn’t hurt; they have fewer pain receptors than humans,” said Rusnak, who is studying how sharks’ robust immune systems are holding up in the “particularly nasty environment of the ocean.”
When a shark is caught, part of the crew holds it down and pours water over its gills. Other members snip a fin clip to study genetic material and the presence of toxins, draw blood to analyze nutrition, reproductive hormones, energy stores and immunology, take a muscle biopsy and use a tape measure to record the shark’s dimensions. If a shark is pregnant, Hammerschlag hooks up a portable ultrasound machine to check on the pups.
“One thing we’re examining is our warmer waters, which means less oxygen and an increase in sharks’ metabolism,” Hammerschlag said. “How does that affect their health and travel patterns? How does it affect their food sources?”
A collective gasp goes up on deck when the next catch is pulled in. It is a rare and critically endangered sawfish, whose long nose, or rostrum, looks like an antique chainsaw. He uses it to shred prey when he’s lurking on the ocean floor. In this case, his teeth tear Hammerschlag’s pants and open a small cut on his thigh. There’s a great rush to set the 13-foot sawfish free immediately, as per federal guidelines.
“I guess this is endangered-species day,” said grad student Roemer.
Roemer works closely with Hammerschlag on the Urban Shark Project, studying how sharks are responding to city growth. They’ve fitted more than 100 sharks with acoustic tags that emit high-frequency signals recorded by 33 hydrophones planted underwater along the Miami shoreline.
These sharks seem to like metropolitan living. They’ve been spotted in the waters lapping at Brickell Avenue condos, behind the Perez Art Museum of Miami and Mercy Hospital, at Dinner Key, along Miami Beach and at Cape Florida on Key Biscayne.
“We’ve got some rock stars pinging all over and a bull shark who never leaves downtown Miami,” Roemer said.
Light pollution doesn’t scare them off and seems to have created a new ecosystem that attracts shrimp and bait fish to fuel the sharks’ food chain. Seawalls and jetties make artificial hiding spots for nurse sharks “who are like ostriches, sticking their heads under ledges,” Roemer said.
They’ve tracked sharks to Bimini, Maryland, South Carolina and Alabama.
“They tolerate boat traffic, although we’ve seen scars and cut fins, and the poorer inshore water visibility seems to be good for them to capture prey,” Roemer said. “We’re also studying natal philopatry: Sharks are known to give birth where they were born but we don’t know why. Magnetic zones? Olfactory clues?”
Some sharks are in trouble. Can they adapt?
"It's incredible to see a species that's survived for 400 million years and is still the top predator of its environment, so you've got to believe in them," said Israel Vallejo, a visiting biology student from Mexico City.
Among Hammerschlag’s recent findings: High concentrations of two toxic contaminants in 10 species of sharks — mercury and BMAA, a neurotoxin linked to the development of Alzheimer’s disease and ALS in humans.
“In South Africa some white sharks have arsenic in their tissues,” said Hammerschlag, who worked with the UM Miller School of Medicine on the study. “They are also ingesting plastic microbeads. We eat what they eat.”
He’s found that in areas where sharks are in decline, reef fish morphology is changing; they’re fatter and have smaller eyes.
“Sharks keep everything in balance like a teacher keeping students in check, but when the teacher leaves, the bullies dominate,” he said.
Hammerschlag co-authored another study showing that expansion of protected home-range areas could safeguard bull, tiger and great hammerhead sharks that were tagged off South Florida and the Bahamas.
He was part of a research team that utilized satellite tagging to conclude that commercial longline fishing vessels target shark hotspots in the North Atlantic and recommended catch quotas to protect sharks from overfishing.
“Sharks are such a charismatic species that illustrate the plight and wonder of the oceans,” Hammerschlag said as his crew motored back to Crandon Marina. “Show someone a photo of a hammerhead and they recognize it.
“I love sharks, and if you see one in the wild or swim among them you will, too.”