Two years ago, Jeff Plumlee watched as his fellow crew members reeled a four-foot long blacknose shark onto the research vessel Capricorn. As they prepared to take the shark’s measurements, they saw something unexpected sticking out of her birth canal: a small tail fin.
“It was indicated to everybody on board [that]… okay, that is a baby shark,” said Plumlee. “She is giving birth on board.”
Quickly, the crew unhooked the shark without taking measurements and released her back into the water so she could give birth safely. Plumlee, who is a PhD student at the University of North Carolina’s Institute of Marine Sciences, helped carry the shark to the edge of the boat for release.
“It was really just intimate, being able to witness it and get the animal back in the water, watch her swim away,” Plumlee said.
Plumlee was searching for sharks off North Carolina’s coast as part of the UNC-IMS Longline Shark Survey. The survey is an effort from the Institute of Marine Sciences to record the diversity of sharks visiting the state over time. It began in 1972 under the late Frank Schwartz, a former professor and marine zoologist at the IMS. As scientists set off to record shark species again this summer, the survey is celebrating its 50th year of data collection, making it one of the longest-running shark research programs in the United States.
Chasing Sharks
North Carolina has a long coastline filled with coastal habitats and features a diversity of water temperatures due to a meeting of warm and cold water currents. These factors, combined with the state’s high amounts of commercial and recreational fishing, result in ocean environments that host a variety of visitors, including sharks.
According to Joel Fodrie, a professor at UNC’s Institute of Marine Sciences with a focus on estuarine and coastal ecology, over 50 different species of sharks have wandered into North Carolina’s waters. Among those, about 20 species are relatively common to spot.
Every other week from April to November, around two scientists and four crew members from the IMS set off on a research vessel to two locations that are four and 13 kilometers off the coast of Shackleford Banks. At each spot, they set out a longline — a 1,000 meter fishing line adorned with 100 baited hooks – and let it soak for an hour. Then, they reel in the catch, counting and identifying the species of each shark that takes the bait.
The researchers record the sex of the shark, measure its length, and collect a tissue sample before releasing it alive back into the water. They also tag it with a phone number so that they can be contacted if the shark pops up somewhere else. The process takes about a minute to four minutes per shark, and the researchers tend to tag anywhere from 0 to 30 sharks per trip.
"The Canary that Drives the Coal Mine"
The survey started off with a goal to distinguish between different shark species in North Carolina. Today, its purpose has evolved to also understand how sharks function as a key player in ocean ecosystems, keeping the predator-prey balance in check.
Similar to a canary in a coal mine, sharks can be indicators of ocean health. Changes in their numbers or diet can reflect changes in water quality or prey populations. But unlike canaries, sharks actively regulate the balance in ocean ecosystems. Sitting at the top of the food chain, they pick off weak and sick animals and keep prey populations from getting out of hand.
“Sharks are a good canary in the coal mine, but they’re also sort of driving the balance,” Fodrie said. “Whereas the canary doesn’t necessarily dictate how the coal mine functions, sharks actually do.”
Plumlee wants to figure out who’s eating who in North Carolina’s marine food web. He analyzes tissue samples from the shark survey for specific chemical patterns that can tell him what that shark has been eating over the past few months.
With that, he can contrast different sharks’ diets, and study how their feeding patterns may change due to high prey populations in the summer.
“These sharks are what they eat,” Plumlee said. “Understanding how they compete, or don’t compete, with each other [for prey] is really important to understanding how sharks impact that ecosystem.”
They’re not scary maneaters: they actually find [humans] not appealing, because we’re too bony, and we don’t have enough meat on us.Savannah Ryburn
A controversial study from 2007 used data from the shark survey to indicate how the loss of sharks can upset the balance of an ocean ecosystem. According to the study, when North Carolina’s large shark numbers decreased in the 1980s, their prey—cownose rays—began to increase in number.
The study hypothesized that the booming cownose ray populations began feeding on bay scallops with less regulation from their shark predators, causing bay scallop numbers to plummet. In 2006, the North Carolina Division of Marine Fisheries closed bay scallop fishing after a meager harvest the previous year.
The link between large sharks, cownose rays, and bay scallops has been disputed in the scientific community. Both sharks and cownose rays have a bigger diet than just one species, and bay scallop populations were also culled by overharvesting and disease. But, the research does hint at how sharks may regulate ocean environments, and how studying them in the long term can clue us into what’s going on under the sea.
“An individual shark may live 20 years,” Fodrie said. “You’re not going to see responses at the community, population level tomorrow if something changes. You’re going to have to work over… probably a couple, three decades, to track numerical changes for something like sharks.”
A Predator on the Decline
One of the trends Fodrie has noticed in the sharks visiting North Carolina over time is a shift in size. A study using shark survey data from 1975 to 2018 found that 10 out of 12 shark species studied were getting smaller over time, with varying degrees of statistical significance.
“Over 40 years of data, pretty much every species, the catches that we’re observing, we’re seeing smaller and smaller fish,” said Fodrie. “And we don’t exactly know all the reasons why that is.”
Threats to shark populations include overfishing and habitat destruction from climate change. Sharks can also be caught and killed as bycatch by fisheries looking for other species. Sharks are slow to become reproductively active, taking anywhere from 2 to over 10 years to mature depending on shark size. This means they are slow to produce offspring compared to other fish, and don’t recover as quickly from population depletion.
Like Plumlee, UNC Chapel Hill masters student Savannah Ryburn is studying sharks’ diets, but with a different goal in mind: conservation. Last summer, she analyzed shark waste to figure out which fish different shark species tended to eat most often. Ryburn hopes that a better understanding of what prey specific sharks eat might lead to more targeted fishing regulation.
“Rather than just putting out a blanket statement, ‘no fishing allowed,’ we can specifically say: okay, with this [fish] species, it’s more commonly eaten by these sharks,” Ryburn said. “Understanding the diet of these sharks can help create more informed fishing regulations to protect the specific sources of these sharks.”
The United States has passed lawsto help conserve sharks, including the Shark Finning Prohibition Act of 2000. The act outlaws shark finning, the practice of removing and selling sharks’ fins and discarding their bodies in the water. Several endangered shark species are also protected from fishing in United States waters.
Despite the threats against sharks, they are a persistent species, having called this planet home for at least 400 million years.
“They’ve been around on the planet longer than trees have, if that tells you how interesting and successful this group of animals have been,” said Plumlee.
Fish on a Mission
Fodrie likes to think about shark research as less about the sharks themselves and more about their connections to the surrounding environment.
“Being a part of the survey and laying my eyes on the [sharks] regularly, it makes them a much more real part of the total community,” said Fodrie. “My interests are in those links between sharks and the other things.”
Sharks tend to inspire fear in the hearts of many beachgoers. Fodrie emphasizes that the odds of a shark death are low. For the most part, sharks commit themselves to three tasks: finding food, finding a mate, and avoiding risk. None of those necessarily involve attacking humans.
“The ocean is their natural habitat, and we have to share it with them,” said Ryburn. “They’re not scary maneaters: they actually find [humans] not appealing, because we’re too bony, and we don’t have enough meat on us.”
As the current scientific lead of the shark survey, Fodrie hopes to serve as its caretaker until the next lead takes over. His aim is for the research to continue informing how we understand sharks and oceans for as long as it can.
“Mathematically, I’m not expected to live until the 100th year,” said Fodrie. “But it would be fabulous.”
