Education

UNC scientists have been chasing sharks for 45 years

A blacknose shark is removed from the line and moved to the science area.
A blacknose shark is removed from the line and moved to the science area. ML Parker/UNC Research

It’s just after dawn as shark scientists from UNC, Duke, and N.C. State gather in front of UNC’s Institute of Marine Sciences, waiting to make a trip to sea in a search for sharks that has lasted decades.

Frank Schwartz’s longline shark survey has sailed the waters off the coast of North Carolina every two weeks through the spring, summer and fall for the past 45 years, making it the longest running shark research program in the country. The study has evolved into a community-wide effort and provides a valuable record of shark populations in coastal waters while also offering research experiences to students.

Schwartz, a well-known shark expert, has been a UNC professor since the 1960s and has made the surveying expedition more than 1,000 times. The only reason Schwartz isn’t climbing aboard UNC’s research vessel, the R/V Capricorn, today is that his doctor recently persuaded him to slow down after more than 50 years of chasing sharks.

But his passion and curiosity remain, so he keeps compiling data from the sea with the help of study caretaker Joel Fodrie, a faculty member in the institute’s Department of Marine Sciences.

TAGSHARK
PhD student Martin Benavides shows NC State undergrad Connor Neagle how to tag the shark. ML Parker/UNC Research

“Some of these shark individuals can live for 10, 20, 30 years or longer,” Fodrie said. “So to have any hope to understand the population ecology of these species, you need studies of that same time scale.”

While the names and faces of students, crew and faculty have changed over the years, Schwartz and the precise methods of surveying sharks remain a constant.

The hours and sampling times remain fixed, departing at 7 a.m. on the dot every other Tuesday. The scientists use the same longline fishing gear – nylon mainlines with 100 case-hardened steel Mustad tuna hooks spaced about 15 feet apart and hanging 6 feet below the surface. Even the silver, 5-inch long Norfolk spot and Atlantic croaker used for bait are the same, caught fresh each trip.

Perhaps the most important scientific constants are the sampling locations. The first line of hooks is set out parallel to the beach of Shackleford Banks where waters are about 42 feet deep. A second set is deployed further offshore in Onslow Bay where the water is up to 72 feet deep.

“Where we’re going today are the same spots he’s been going since 1972,” says Kerry Irish, who heads communications and outreach at the Institute of Marine Science. “That gives the study and its data incredible power.”

Smaller sharks

Having a record of 45-years of data allows Schwartz, Fodrie and their colleagues to follow population trends of many of North Carolina’s shark species.

One pattern they have noted is a decline in large shark species. From the 1970s until the early 1990s, they regularly sighted large bull sharks and tiger sharks, but in recent years, most are smaller species such as Atlantic sharpnose and blacknose sharks.

The decline in large sharks is a cause for concern, because they play vital roles in the coastal ecosystem by keeping “mid-level” predators such as rays in balance and thinning the ocean of older or weaker animals. Much like the wolves that once kept deer populations in check on land, a healthy shark population helps maintain the natural balance of the ocean.

“Sharks can be an indicator of ecosystem health,” said Fodrie. “We don’t often think of sharks as ‘canaries in the coal mine,’ but in fact they probably play that role.”

Changes in water and air temperatures could have an effect on sharks, but the suspected culprit for the decline is fishing – either overfishing of the sharks themselves or of the fish they feed on.

SHARK FACE
PhD student Martin Benavides holds a blacknose shark. ML Parker/UNC Research

But recent shark management efforts have begun to focus on conservation, and the longline survey data may be starting to reflect that work. Fodrie said that they’ve recently begun to see tiger sharks again.

“It may be that now we’re in a phase where we may be seeing some recovery,” said Fodrie. “That really stresses the value of these long-term data. This survey has been done long enough to perhaps capture the ups and downs of populations that are affected by climate or fishing.”

The story will continue to evolve as more data are collected, and although optimistic, Fodrie stresses that it is too early to make any definitive conclusions about the recovery.

“This is not something where you get instant gratification,” said Fodrie. “These aren’t fleas, and you can’t understand how populations cycle over a few weeks or a year.”

Sea legs

Although the shark researchers can control most factors in their survey, weather is not one of them.

This morning, the Capricorn’s captain is keeping a close eye on the weather. Strong ocean winds and high seas could make for an unusually rough trip, though it’s not bad enough to stop the researchers from sampling at least one location.

After 45 minutes of choppy travel, the captain reduces speed and the crew begins collecting fresh bait. A trawling net is deployed and dragged behind the Capricorn, scooping up schools of fish and colonies of shrimp. Twenty minutes later, the net is winched out of the water and the haul of bait spills onto the swaying deck.

The crew seems indifferent to the turbulent water, and begins baiting the hooks and dropping the line into the water at the first sampling location.

The longline, marked with floating orange buoys, stretches nearly half a mile behind the Capricorn. The crew leaves the baited line in the water for exactly one hour before pulling it in one hook at a time, consistent with the methods Schwartz established four decades ago, said Martín Benavides, a doctoral student studying coastal shark ecology in Fodrie’s lab.

As the line is brought in, most hooks are empty. But when the first shark is seen on the line, an Atlantic sharpnose, it is quickly brought aboard. The team works swiftly and identifies the species and sex, and measures the fork length – tip of the jaw to center of the tail indentation. Benavides records everything in a small yellow lab book.

All live sharks are tagged with an identification number, and after just a few minutes, returned to the sea. Today’s catch yields seven sharks, all Atlantic sharpnoses, “Pretty good given the conditions,” according to Benavides.

We all work together

In addition to maintaining Schwartz’s long-term survey, researchers and students from other institutions, including Duke and N.C. State, often collect data for their own projects. Collaborations like these have become essential, as money and resources such as the Capricorn become increasingly scarce.

“That’s the nice thing about all of these labs down here,” Irish said. “Everybody does something slightly different, so we all work together.”

In addition to helping the Institute of Marine Sciences team identify, measure and tag sharks, UNC Wilmington graduate student Ashley DeLeon uses small biopsy tips to collect muscle samples from behind the dorsal fins to further her own research on the differences between muscle fibers from coastal and open water sharks. Back in the lab, DeLeon will analyze the samples using high-powered microscopes to view the internal components of the muscle cells.

She hopes her research will help with conservation efforts, but her foremost concern on the Capricorn is the well-being of the sharks. “It’s really quick and doesn’t stress the animal,” she said. “If I feel it is already stressed, I won’t take the sample.”

A few feet away, NCSU sophomore Connor Neagle is working on a project that compares the dimensions of the pectoral fins of different shark species. He helps Benavides with tagging and then snaps photos of each shark that allow him to make detailed measurements later.

Neagle hopes that his findings can be applied to “bio-inspired design,” a process that uses natural organisms as an influence for designing materials or machines.

“Marine science is very collaborative,” Neagle said. “Lately I’ve noticed that more and more groups are collaborating and sharing their data with one another, as well as their resources.”

Jeremy Frieling: 919-829-4826

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