by Alicia Wolfram
They don’t sip CRUcumbers at CRU or wait in line at Juice Bar, but they’re back every summer. A month ago, on Friday July 18, just in time to kick off Shark Week, a 1,653 pound great white shark pinged 50 miles east of Nantucket. Named “Contender,” he is the largest male white shark ever tagged by research group OCEARCH in the Western North Atlantic. While well offshore, his appearance is a timely reminder that sharks, too, summer on Nantucket.
But despite the great white’s celebrity status, it’s not the species beachgoers are most likely to encounter on Nantucket. According to local shark researcher and Ph.D. student Caroline Collatos, that distinction belongs to the sandbar shark — also known as the brown shark.
“They’re the shark you’re most likely to interact with if you’re on our shoreline,” she said.
Sandbar sharks are abundant in Nantucket’s nearshore waters during the summer, especially around Great Point, where Collatos conducts much of her fieldwork. She credits the calmer currents and unique underwater topography on the inside of Great Point—shallow flats that drop off to 40 or 50 feet close to shore—for drawing the sharks.
“I find them much more dense in their numbers there than I do around other portions of the island,” she said. “I must have seen 30 today driving along the beach.”
The slower water movement on the west side of Great Point—in contrast with the strong currents along the south shore—makes it an ideal spot for these energyconscious predators, who, unlike other fish such as tuna, do not feed constantly and need to maximize energy efficiency.
“For sharks, the name of the game is energy conservation,” Collatos said. “They’re not eating every day, every hour.”
These sharks typically arrive in mid-June and leave by late September, responding to water temperature and shifts in daylight—cues that guide their migration patterns.
And while sandbar sharks may be the most common, Nantucket waters host a surprisingly diverse lineup. John Chisholm, shark researcher and adjunct scientist at the New England Aquarium, noted that spiny dogfish, basking sharks, sand tiger sharks, dusky sharks, makos, smooth hammerheads, and porbeagle sharks are all part of the region’s seasonal ecosystem.
With the rise of smartphones, social media, and growing public interest, Chisholm now receives dozens of reports a day during peak season. “But if you talk to the people that have lived on the island and the fishermen in particular, they know that the sharks have always been there,” he said.
When a shark is spotted, Chisholm reviews photos and videos to identify the species. He attributes the uptick in sightings to species protections and increased reporting. “It’s really a combination of factors—the protection that they’re afforded and also the fact that more people are out there reporting them,” he said.
Understanding when, where, and why sharks are present around Nantucket starts with research. Chisholm and Collatos, along with organizations like the Atlantic White Shark Conservancy (AWSC) and OCEARCH, are leading efforts to tag and track sharks throughout the Northeast, helping to demystify shark behavior and improve public awareness.
AWSC maintains a photo identification database of more than 700 individual white sharks in the Western North Atlantic. Much of that data is made publicly accessible through the organization’s White Shark Logbook, as well as its Sharktivity app, which allows users to report sightings and track sharks tagged with acoustic and Smart Position and Temperature (SPOT) devices.
Collatos’ own work focuses primarily on sandbar sharks, a federally protected species, and how they interact with the island’s waters. Each summer since 2020, she has been catching, tagging, and releasing sharks off Nantucket and using the data to study the demographics of species around the island. To date, she has caught and released more than 200 sandbar sharks, and her tagging studies reveal patterns of habitat use and residency, providing insights into why these sharks are drawn to certain parts of the island and how long they tend to stay.
Collatos’ research on sandbar shark movement and behavior may also provide cues about shifts in the local ecosystem. If ocean temperatures in the Nantucket Sound continue rising over the next five to ten years, she suggests their migration matters could change—with sharks arriving earlier, staying later, or traveling farther north. In a recent article for On the Water magazine, she describes sandbar sharks as “valuable bioindicators of the health and stability of our local marine environment.”
Warming waters are already beginning to influence which species appear near Nantucket, according to Chisholm, with sightings of typically southern sharks like spinners and black tips becoming more common.
Using rod-and-reel techniques that mirror those used by recreational anglers, Collatos can also assess how the sharks fare after being caught and released. This helps researchers better understand post-release mortality, a critical factor for conservation in areas with heavy recreational fishing activity.
This year, the National Oceanic and Atmospheric Administration (NOAA) is conducting a population survey to assess the current status of the species.
Sandbar sharks were heavily overfished in the ‘80s and ‘90s, primarily for their fins, Collatos explained, leading to an 80% population decline. Federal protections enacted in 2008, which banned retention of the species once caught, helped initiate a slow but steady recovery. This year’s stock assessment is expected to provide a clearer picture of how far they’ve come.
White sharks, too, have seen a rebound over the last 10 to 15 years, according to Ashleigh Novak, Research Coordinator at AWSC.
She points to a combination of protections that made recovery possible: federal listing of white sharks as a prohibited species as well as the Marine Mammal Protection Act, which helped gray seal populations rebound and restore the sharks’ food supply.
“It’s a conservation success story,” Novak commented.
Despite their often-misunderstood reputation, sharks play a vital role in maintaining a balanced ocean ecosystem. As apex predators, they keep mid-level fish populations in check and support the stability of species further down the food chain.
And while sandbar sharks are at the top of the marine food chain, they are not known to be aggressive to humans. “They are not affiliated with unprovoked attacks,” said Collatos, explaining that ‘unprovoked’ refers to cases where a person is simply swimming and not interacting with the shark in any way.
“You just look at how many people are in the water every year, every day during the summertime, and how few incidents we do have,” said Chisholm. “But that being said, we have had incidents, and people have to respect that they’re going into the sharks’ world when they go in the water, and they need to take appropriate measures to make sure they’re safe.”
He said one of the biggest misconceptions is that sharks are actively looking to bite humans. “And they’re really not—they’re for the most part not interested in us at all,” he added.
New technologies are helping scientists get a shark’s-eye view of what really goes on beneath the surface. AWSC uses camera tags attached to the sharks’ musculature that record underwater footage and movement via accelerometer.
“Ninety-five percent of the time, they’re just swimming,” Novak said. “They’re not mindless eating machines out there.”
Being “shark smart” means checking the Sharktivity app, avoiding areas with visible baitfish or seals, swimming in groups close to shore, and avoiding excessive splashing. If a shark is spotted, lifeguards follow strict protocols.
Nantucket harbormaster Sheila Lucey explained that when a shark is confirmed within the swim zone, the beach is closed for two hours, and if the shark is outside the swim zone, the beach closes for one hour. The shark flag is raised, alerts go out via ATVs to other unguarded beaches, and notifications are issued through social media and local radio.
During the month of July, a number of beach closures have occurred due to confirmed sightings. With 60 lifeguards rotating across the island’s beaches, coverage is strong.
“They’re asking you to get out of the water for your own safety,” Lucey said, “and we’re just trying to keep everyone safe.”
Advances in technology are transforming tagging data into concrete safety insights, helping researchers and the public better understand how to coexist in shared waters.
“One of the tagging technologies showed that when [great white] sharks are here and present, they’re spending about 50% of their time in water 15 feet or less,” said Novak.
This kind of information is crucial for developing effective beach safety guidelines and educating the public about when and where sharks are most likely to be present.
On July 16, OCEARCH teamed up with the Nantucket Triathlon and Cisco Brewers to host the White Shark After Party—an event for the local community to support important research, complete with live music and craft beer.
“We’ve had the privilege of working alongside the Nantucket fishing and marine communities for years. Their support has been invaluable to our research, particularly in understanding the migratory patterns and behavior of white sharks in the North West Atlantic,” said Chris Fischer, OCEARCH’s founder, who was present at the event.
Jay Harman, CEO of Cisco Brewers, shared in a statement the inspiration behind the collaboration: “Years ago, we wanted to create something special that honored OCEARCH’s incredible work in shark research, and Nantucket’s role in this scientific journey,” explained Harman. “Our Shark Tracker Light Lager was born out of that vision—celebrating the sharks that visit our waters and the people dedicated to protecting them. We’re thrilled to continue this partnership with OCEARCH and the Nantucket Triathlon to bring the community together for this important cause.”
