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‘A constant presence.’ What to know about white sharks off Cape Cod
At first there is only a sense of slow movement through a veil of murky water, methodical and restrained like a cat coiling up for a pounce. Within seconds, details begin to emerge — the sharp edge of a dorsal fin, then one pectoral fin, then the other. Leading lines of a pale gray body, muscled and sleek, undulate under the power of an unseen caudal fin. Then, sudden acceleration, moments of chaos. Flashes of sandy bottom below, the rippling surface above.
You are riding along with an Atlantic white shark on the hunt, a scene captured by a camera tag tethered to the shark’s back by a small intermuscular dart. And it all happens in about five feet of depth in the nearshore waters of the Outer Cape.
This kind of footage, shared Tuesday at a briefing about the 2023 white shark season and ongoing research at the Chatham-based Atlantic White Shark Conservancy, is helping scientists understand the predator’s behavior — knowledge they can use to inform public safety policy and educate the public about being shark smart when they visit Cape beaches.
It’s an especially important task on the Cape, where the steadily growing white shark population comes to hunt in the same waters where people swim.
Greg Skomal, a senior biologist with the Massachusetts Division of Marine Fisheries who studies the Cape Cod white sharks alongside conservancy scientists, described how the shark “moves right up into the shallows.”
More:First white shark of the season sighted off Provincetown, public reminded to be aware
“You’ll see the sand, you’ll see the surface, and you ultimately see the shark fail,” he said. “And so the questions are: how often does it do this, what are the conditions that precipitate this, is there anything unique about those conditions, is it a certain time of day, is there a certain tidal cycle?”
White shark population has grown over the last two decades
“In terms of white sharks we can definitely say 20 years ago we didn’t have anywhere near these numbers,” Skomal said.
Skomal and Megan Winton, a conservancy staff scientist, said the number fluctuates over the season as sharks come and go.
Last year, 134 previously tagged sharks were detected by 69 receivers concentrated along the Outer Cape and into Cape Cod Bay, and also deployed off Nantucket, along the South Shore and up to Cape Ann. The greatest concentrations were on the Outer Cape, especially from Chatham south to the Monomoy Islands. By comparison, 130 previously tagged sharks were detected in 2021, 116 in 2020, 99 in 2019, and 63 in 2018.
Since 2009, a total of 303 sharks have been tagged. That includes 31 sharks tagged last year. At least 24 new visitors who were not tagged showed up last year. They were identified using underwater video monitoring. Since 2014, the researchers have recorded more than 600 individual visits.
All of the data is now publicly shared on an interactive web application accessible via the conservancy’s website: the White Shark Logbook, which the scientists have been building over the last couple of years.
Sharks are coming to feast on seals
Attracting the sharks is a dense population of seals, whose numbers are rebounding in the northwest Atlantic as a result of federal protections put in place in the 1970s after intense hunting over the last couple of centuries.
“And in response to the growing seal presence in our nearshore areas, white sharks are returning to what they once did, and that is hunting close to shore,” Skomal said.
More:‘The shark has to cooperate’: Researchers tagged 31 great whites off Cape Cod in 2022
With the expansion of commercial and recreational fishing, the number of white sharks dropped in the ’80s and ’90s. But since they were listed as a prohibited species in the northwest Atlantic in 1997, their numbers too are rebounding.
“And so we now have overlap of sharks and seals,” Skomal said, and “sharks are hunting seals in shallow water with people.”
Using technology to understand white sharks ‘minute to minute,’ and warn swimmers
From acoustic tags to real-time receivers, video camera and data collection packs, and drones, scientists are pulling out all of the stops to get to know every intimate detail of the white shark population.
The camera tags used to collect data and video, like the one shown at Tuesday’s briefing, are increasingly favored over the standard acoustic tags. They can either be tethered via a dart, or clamped onto a shark’s dorsal fin, and fall off after about 11 hours. They record data 20 times a second.
“We’ve had several deployments using camera tags to study really, really fine scale behavior. Some of our previous work looked at what these sharks were doing from week to week, or month to month, even from year to year broad scale migration and such,” Skomal said.
But the emphasis has shifted “to know what these animals are doing hour to hour, minute to minute, even second to second,” he said, “and this technology allows us to do that.”
‘Like were giving smart phones to white sharks’
“The way I like to describe it, it’s really like we’re giving smart phones to white sharks,” added Winton. “They are outfitted with an incredible array of sensors that tells about the animals’ movements and their environment and we can see exactly what they’re doing, which is huge.”
The whole point, she said, “is to get a better understanding of their predatory behavior.”
Winton said the researchers want to deploy more camera tags this season.
Real-time receivers alert public safety officials ‘within seconds’ of a shark detection — but they’re pricey
Another important tool they’re using are solar-powered, real-time receivers, which can send alerts to lifeguards and other public safety officials within seconds of a tagged white shark coming in range — this has been piloted with success at Wellfleet beaches. At $16,000 per device, the number of deployments is limited.
Skomal has acquired some funding from the Office of Naval Research, the conservancy bought one, and more recently National Geographic purchased a couple. Marshfield is also the first town to invest in two of its own real-time receivers.
On the Cape, real-time receivers are deployed at North Beach in North Chatham, Nauset Beach in Orleans, Maguire Landing at Lecount Hollow and Newcomb Hollow Beach in Wellfleet, and Head of the Meadow Beach in Truro.
Things to know:‘Everyone going into the ocean should exercise caution’: Reduce the risk of a shark attack
Absent more receivers, the conservancy shares the real-time alerts from existing receivers to the wider public by tying in its Sharktivity app, which provides information and push notifications to users on white shark sightings, detections and movements.
Drones, which made their debut last summer, are also helping researchers.
“Drones have become a really incredible tool for studying behavior remotely,” said Winton, noting they allow for multiple sharks to be monitored at once to see how they’re using nearshore waters.
The conservancy is working with the Center for Coastal Studies, in Provincetown, to continue trying the technology out this season, she said.
‘Essentially a constant presence’: Changing perceptions & behaviors
The instant relay of information from the real-time receivers to lifeguards to swimmers “seems to be really changing people’s perceptions of how white sharks use our waters,” Winton said.
“Some of the lifeguards we’ve worked with have mentioned that they used to think that white sharks occurred every once in a while,” she said, “but now they realize that they’re essentially a constant presence off their beaches in the summer and the fall, which is really powerful. That’s a big shift in perception.”
One big takeaway is that the sharks are spending time in shallow water, even right off the surf line. Skomal said most people focus on wanting to know distances from the beach sharks might be present, but “it really has more to do with depth.”
The scientists advise people venturing into the water “to watch their depth” if they go in — Skomal generally goes in only waist deep — and to look for the presence of seals or lots of birds before deciding to go into the water.
That said, they emphasize that shark attacks in general are “a very rare event.”
“These animals are really good at what they do. They’re very cautious, skilled hunters,” said Winton, “but anytime you have large predators overlapping with people, which they do here, there’s a potential for that animal to make a mistake. But people can make proactive decisions to reduce their risk.”
Heather McCarron writes about climate change, environment, energy, science and the natural world. Reach her at [email protected], or follow her on Twitter @HMcCarron_CCT
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