NC shark researchers tag and release sharks in NC rivers
Sharks are the kings and queens of the Carolinas food chain, but they’re not well understood. North Carolina researchers are working to change that.
Steven Spielberg’s 1975 thriller featuring a man-eating great white debuted more than 40 years ago, but its visceral images of an apex predator with a taste for human flesh still evoke fear today that is often largely unfounded.
Researchers in North Carolina have been studying sharks continuously for nearly five decades. In that time, they’ve gotten to know the sharks in Carolina waters better than almost anyone.
Twice a month in the summer, researchers cast a milelong nylon line with 100 baited hooks into the ocean.
They’re hoping to catch sharks — all sizes and varieties — to help track the health of the predators that lurk in the mid-Atlantic and learn how they reflect the health of the ocean and its ecosystems.
University of North Carolina Institute of Marine Sciences (UNC IMS) researchers have caught and tagged dozens of shark species over the years, collecting data and observing trends. It’s one of the longest shark surveys in the world.
The survey’s research trips off the Carolina coast are between April and November in two areas — one about two miles and another about seven miles off the coast of Shackleford Banks, said Martin Benavides, a Ph.D. candidate at UNC who has been working on the survey for about three years.
Any sharks caught on the longline — attached to floating buoys every 10 hooks — are ID’d and released. Researchers measure the sharks, and sometimes take clips of the sharks’ fins for DNA testing, Benavides told The News & Observer.
The survey’s research can help not only determine the health of the shark populations, but also take the pulse of how healthy the ocean is.
‘Loss of the great sharks’
There are about 45 different shark species found off the North Carolina coast. The longline surveys have caught about half of those species so far, Benavides said.
Since sharks live longer lives — from a few decades to more than 100 years — it takes considerable time to gather data to help understand them and observe any patterns, Benavides said.
One pattern the survey observed in research published in 2007 was “a loss of the great sharks, those top predatory sharks that were once much more common” during the early years of the UNC IMS survey, Benavides said.
But a lot has changed since the start of the survey in the 1970s, which is also, coincidentally, when “Jaws” first hit theaters.
Larger sharks seem to be on the decline, while mid-level predators are more common.
“Some of those sharks that were once common have all but disappeared in the later survey,” Benavides said. “The largest shark species seem to have been declining.”
Once common bull sharks, which can grow to be more than 11 feet long, haven’t showed up on the longline for at least 12 years, Benavides said. Dusky sharks, which can grow to about 10 feet and are considered endangered in the U.S. Atlantic, also once were common in the survey and now “we almost don’t see them anymore.”
Other sharks are getting smaller, including blacknose and blacktip sharks. And Benavides said half of the species he’s studied have seen a drop in the size of the largest sharks.
“We’re seeing the loss of the largest individuals,” he said.
There are several variables that could explain why some sharks appear less often — or not at all — on the survey now, including overfishing, which contributed to a sharp decrease in the number of larger bull and tiger sharks in the 1970s, Benavides said.
But there are some signs that more resilient species of larger sharks like tigers — which mature faster and have larger litters of pups — could be recovering. While the tigers had all but disappeared from the survey in the early 2000s, researchers now see one or two each year.
Healthy sharks, healthy earth
Understanding sharks — their populations, size, health and behaviors — can be a indicator of overall ecological health, Benavides said.
“Being top predators, they biomagnify,” he said. “Anything happening on the food chain will ripple up to them. Some people get alarmed as we talk about shark population recovery. But I think that is a sign of a healthy ecosystem.”
It’s uncertain if North Carolina will see a full recovery of its larger sharks.
“I don’t know if we can ever expect to go back to what it was, say, in the early 70s,” Benavides said. “But some of the larger shark species are showing signs of coming back. We’re starting to get a glimpse of another shift coming. And that’s a good sign for our coastal waterways, hopefully.”
North Carolina may have fewer large sharks, but it could be home to a greater number of sharks.
“With the loss of larger outliers, we’re also catching and releasing more sharks in general,” Benavides said.
During a June outing, the crew caught 25 sharks — the most for a single day in recent years of the survey.
The shark most commonly found on the longline survey recently is the Atlantic sharpnose, which can grow to about 3 feet long, Benavides said.
While only a handful of sharpnose were caught in a whole year of surveying in the past, now Benavides said they can catch 20 or so during a single trip.
Sharks in Carolina rivers
Researchers also are looking into the sharks that make North Carolina’s rivers their homes.
Health of shark populations in the ocean is an indicator of the health of the oceanic ecosystem. The health and number of sharks in rivers can be an indicator of water quality, researchers say.
Charles Bangley, a researcher with the Smithsonian Environmental Research Center and who also completed shark research at East Carolina University, is working with a team to study sharks in the Cape Fear. Bangley also is working with UNC Wilmington Biology professor Kara Yopak, whose research features a study of shark and ray brains and behavior.
It’s the first time sharks in the Cape Fear River have gotten attention from researchers since the UNC IMS conducted a study in the 1970s.
Bangley and the team have been working for about two years, catching sharks that, up until recently, haven’t gotten a lot of tagging attention. Those include smooth dogfish, blacktip, spinner, bull and dusky sharks. Some of those sharks are major conservation concerns.
Smooth dogfish and blacktips are among the most commonly landed sharks in commercial and recreational fishing. The population of North Carolina Dusky sharks “crashed really hard” in the ’80s and ’90s, Bangley said. It could take a century or more to rebuild that population, he said.
But while some sharks may be on the decline, Bangley’s research shows others feel comfortable in North Carolina rivers.
The sharpnose and sandbar sharks seem to be using the Cape Fear as a nursery for their pups, including the area from where the river meets the Brunswick River in Wilmington, to the mouth of the river, Bangley said.
Bangley’s research already showed that bull sharks are increasingly using the Pamlico Sound as a nursery as the sound’s waters grow warmer and salinity increases. Before about 2011, there was little evidence of a nursery in the sound.
Because a shark pup’s primary natural enemy is a larger shark, rivers provide shelter for the vulnerable young, Bangley said. And estuaries can be productive areas to hunt.
“There’s a lot of practical applications for knowing where sharks are and when and why,” Bangley said. “It helps us understand a highly migratory species so we can educate fisheries, set aside protected areas for nursery habitat and understand the health of the ecosystem. Sharks are at the top of the food chain, so seeing them choose the Cape Fear can reflect high-quality habitat.
“Sharks can be sensitive to environmental changes, so if sharks can be supported, that’s potentially a good indicator for overall ecosystem health.”