Like many a tourist, white sharks come to Cape Cod for the fresh seafood and sunny beaches.
The sharks don’t sunbathe on the sand but their favorite prey, gray seals, do and when seals venture back into the waves they become a target.
“White sharks are feeding on seals in shallow water off Cape Cod,” Greg Skomal, the Massachusetts Division of Marine Fisheries senior shark researcher, observed at the Atlantic White Shark Conservancy’s media day June 29 at its Chatham headquarters. “A predator prey relationship is natural in any system. We are studying various aspects of this behavior.”
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Skomal’s studying that relationship because cruising for seals in shallow water brings sharks into conflict with swimmers, surfers, sailboarders and even waders. There was a shark fatality in 2018 when Arthur Medici of Revere was bitten off Newcomb Hollow Beach in Wellfleet. That changed the direction of Skomal’s work from tracking sharks in their travels across the Atlantic to fine scale monitoring close to shore.
“Sharks spend half their time here in 15 feet or less of water,” said Meg Winton, Atlantic White Shark Conservancy staff scientist and Ph.D. candidate.
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That’s where beachgoers spend their time as well so the goal is to learn when. where and why sharks come in close and to use that data to improve public safety at Cape Cod beaches.
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Tagging sharks acoustically
Early in the last decade, Skomal was using satellite tags to learn where great white sharks go when they’re not here. The tags would collect tracking data, transmit to a satellite and then download the travel information. That provided a wealth of new information, but to reduce encounters the researchers needed finer and more immediate information.
“We’re looking to find when and where white sharks feed on seals,” Skomal said. “We’re observing sharks using state-of-the-art technology trying to find patterns in their behavior tied to statistical probability. We’re hoping that information will enhance public safety.”
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The researchers are using acoustic telemetry. Transmitters attached to the sharks send a high frequency sound signal that’s picked up by an array of receivers on buoys scattered not only around Cape Cod but up and down the Massachusetts coast and beyond by other agencies. Denser arrays of receivers in grids at select locations off Cape Cod allow for finer scale data on shark movements. Linking that to maps of the sea floor and sandbars provides detail on patterns in shark activity. During the last two years live receivers have been tested.
Real-time live shark tags
“Standard receivers (in buoys) log the data and you have to go out and retrieve it (every few weeks). Live receivers transmit in real time. Most are at beaches like Newcomb Hollow and Lecount’s,” Skomal said. “It does provide real-time information that lifeguards can use; when the sharks are there, how long they stay there.”
The live receivers cost $16,000 each. The acoustic receivers are $2,200.
The higher cost and issues with durability have limited their deployment.
“We have five real-time receivers out there and 70 to 80 acoustic receivers. In all there are about 200 (acoustic receivers) in Massachusetts waters,” Skomal said.
The buoys take a pounding.
“The solar panels fail the fastest. They’re repeatedly hit by heavy waves,” Skomal said. “There is leakage within the system. They get beat up. The units last year started failing in August. We keep them on the shelf so they can be swapped out. The components are all built by different people. So this year we’re testing larger buoys to see if they withstand the elements.”
Winton said not all sharks are tagged. The live data will only let someone know if a tagged shark is near. As of June 29, Skomal said 283 white sharks have been tagged, 268 with acoustic tags, 72 with the pop-up satellite tags and 25 with railing cameras. More than 500 different white sharks have been identified visiting the Cape, Winton added. So if no sharks show up on a live feed that doesn’t mean there are no live sharks out there.
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Still the live data is useful, telling lifeguards when sharks are likely near shore. The information is also available on the AWSC’s Sharktivity App.
The Center for Coastal Studies in Provincetown is also collaborating with the state in creating the grids of arrays.
“In a fine scale array the receivers are so close you can triangulate the exact position of the sharks,” Skomal said. “Bryan Legare (of the Center for Coastal Studies) is putting them out today at three more beaches.”
Paired with detailed surveys of the sea floor and other data from the arrays, this allows the scientists to model shark movements and habits.
“We’re going from weeks and days to minutes and seconds,” Skomal said. “Bryan maps the habitat so we can monitor the sharks through the habitat. If you get a deep trough between the sandbars there could be a shark hunting in that trough.”
The sharks do seek deeper water when they travel inshore in search of seals. Researchers know that is because of camera tags they’ve employed.
The camera tags also record temperature and depth information and tell the scientists when the shark is accelerating in preparation to attacking a seal. They’re attached with a dart to the fin and the camera is tethered to that. After a few days the unit detaches and floats to the surface
“It’s an incredible piece of technology,” Winton said. “It‘s an activity tracker and gives us 20 data points a second. It gives us a detailed look into what the animal is doing and can record 11 hours of video footage.”
They have video of some attempts at capturing a seal, but data on actual predation events is limited. They can’t yet predict when the sharks are most likely to be looking to feed – which would be useful to know in terms of public safety.
“For each predatory event there’s a whole suite of environmental information we collect. We’ve deployed the camera technology 25 times but the patterns aren’t there yet,” Skomal said.
There is speculation that dawn and dusk might be worse times for a person to be in the water, but it’s hard to say. He recommends not swimming at those times.
Drones and sharks
They’re also trying out a new technology: drones. The drone, essentially a blimp which is controlled by an operator on the beach, has been tested at Nauset Beach. It operates from a fixed location. However turbidity and choppiness in the water can make it difficult to spot sharks. Last summer the blimp spotted 30 sharks. Were there more it missed?
”We don’t have a good idea how efficient that is in spotting sharks,” Winton said. “We had 254 seal sightings. We wanted to get a feel for how much sighting conditions change over time. Conditions can change dramatically over the course of the day. We will incorporate the drone as well as part of the fine scale acoustic arrays.”
They’ll compare the drone data with the acoustic data from the arrays to see how accurate the drone is.
“We’ll see how many sharks are swimming through that area that we’re not seeing,” Winton said.
What we know of sharks
The conservancy and Skomal have a decade’s worth of data on some of the sharks they’ve tagged.
“Some sharks spend the summer. Some pop in and out,” Winton said. “Some sharks are regulars for years and then show up somewhere else. It’s a fluid dynamic what sharks are here year to year. They are a coastal species. Why didn’t they show up as often as they do now? It’s because seals were extirpated. So the seals are the draw.”
“There’s so much variability within the species that finding patterns is really difficult,” Skomal added. “The patterns don’t pop out.”
August, September and October are the peak months of shark activity of Cape Cod, They like the warmer waters of late summer.
“In June it starts to ramp up. That depends on the water temperature. As soon as you start to have storms and a drop in the water temperature the sharks leave,” Skomal said.
Winton said a shark was detected Jan. 6, but overall shark presence depends on water temperature.
“White sharks like water temperatures in the 50s to 70s. If the water temperatures continue to warm we could see a change in seasonality,” Winton said.
“We want to look at climate change’s impact on seals,” Skomal said. “We don’t have a firm handle on that. That work is conducted by the National Marine Fisheries Service. They estimate the whole population at half a million. We think there are 25,000 to 45,000 seals on the Cape.”
That’s a lot of potential food to attract sharks.
More sharks are tagged each year and Skomal said beachgoers have modified their behavior due to the increased presence of sharks.
“I do see some changes,” he said of human behavior in response to a question if shark attacks are likely to increase. “It’s such a low frequency event it’s difficult to predict.”
Atlantic White Shark Conservancy efforts
The Shark Conservancy is responsible for much of that with education efforts. The organization was established 10 years ago, “to support shark research and to help improve public safety, to educate the public and inspire shark conservation,” AWSC CEO Cynthis Wigren said.
The Shark Smart outreach program for beach safety has engaged with 1,400 students this past year. They’ve also sent Shark Smart ambassadors out to the beaches to reach the public.
The AWSC’s biggest fundraiser the Great White Gala is coming up July 21, at 6 p.m. at the Wychmere Beach Club in Harwich. The AWSC also runs shark spotting and eco-tour charters, at $2,500 a trip. The spotter plane boosts the expense. The AWSC makes about $250 to $500 per trip when expenses are factored in.
Staff writer Rich Eldred can be reached at [email protected].