Sandbar Sharks Around Nantucket 

Every summer, sandbar sharks return to Nantucket to take advantage of the island’s ideal conditions: water temperature, depth, and tidal currents — particularly off Great Point. Though they’re predators, sandbar sharks are non-aggressive and have not been affiliated with unprovoked attacks on humans.

“Individuals are coming back to the island pretty much at the same time every year, pretty similar to the summer crowd,” said Caroline Collatos, a Ph.D. candidate at UMass Boston working with the New England Aquarium, who has spent the last five years studying and tagging local sandbar sharks as part of her dissertation about the species’ residency along Nantucket’s shoreline. She presented parts of her research as part of the Linda Loring Nature Foundation’s Science Pub Webinar Speaker Series and hopes to finish her dissertation in December. Caroline also grew up spending summers on Nantucket and lives there most of the year. 

Massachusetts marks the northernmost region of sandbar sharks’ coastal migratory pattern. Along the U.S. East Coast, the species ranges from Florida to Massachusetts, spending summers in the north and winters down south. They reach sexual maturity at around 15 years and produce an average of nine pups at a time, which is considered a slow-growing population.

Sandbar sharks have long been a preferred species in the commercial shark fishery and were historically overfished, with stock reductions estimated at nearly 80 percent before federal and state protections were enacted in 2008. Since then, the population has shown signs of rebounding. While the species is still considered “overfished” — meaning overall numbers have not yet fully recovered — overfishing is no longer occurring. In Massachusetts, anglers can catch sandbar sharks but are prohibited from keeping them.

When it comes to local data, however, the Bay State is lacking. Greg Skomal conducted fishery research in the region from 1989 to 2002, primarily around Martha’s Vineyard. “Skomal was the first person to collect data in this area,” Caroline said. Since then, little focused research has examined how sandbar sharks are using the Nantucket Sound. 

Part of Caroline’s work in collaboration with her advisors also examined post-release mortality. As catch-and-release fishing has increased, she wanted to know: how are the sharks faring after being returned to the water? It turns out they are “pretty hardy and mostly surviving the catch and release fishery,” she said.

The bulk of her research focuses on population demographics and habitat use in the Nantucket Sound. Since 2021, she has caught and tagged sharks off Cape Cod and Nantucket using acoustic telemetry tags, devices she compares to an EZ-Pass system. Scientists implant the tags internally, and they ping nearby receiver stations as the sharks swim past. There are 43 receivers positioned throughout Nantucket Sound, deployed each May and retrieved in November, and they’re part of a shared network stretching from Maine to Texas. The system allows scientists to monitor sharks passively, “a way to monitor them without interfering with the animal’s natural movements,” Caroline said. 

Another tool, called an ADL tag, is attached to the dorsal fin and records body position, acceleration, and movement. Some are also equipped with cameras. 

Over the last six to seven years, Caroline and her team have caught 276 sandbar sharks. The average individual measured about 150 centimeters — roughly 4 feet, 9 inches. Most of the sharks are juveniles and adults rather than newborn pups, and researchers are seeing significantly more females than males, a pattern that “could be a factor that’s due to their sexual migration after maturity,” she explained. 

Between 2021 and 2025, the team tagged 76 sharks in Massachusetts. An additional eight were tagged in New Jersey prior to 2021, bringing the total to 84 tagged sharks. Of those, 83 have been detected by receiver stations. “I’d like to say that’s amazing,” Caroline said. 

On average, sandbar sharks stay around Nantucket for about 28 days, though some individuals have remained as long as 93 days between June and November. And they’re not randomly dispersed.

Strong habitat use has been documented around Great Point, specifically the west side.“Sandbar sharks like this Great Point area,” Caroline said. “July, August, mid September, you’ll likely see sandbar sharks cruising the coastline. You might mistake them for seals. If they don’t come up for air at all, they’re most likely not a seal.” 

So why Great Point? Sandbar sharks, and many shark species, must swim continuously to breathe. The waters off Great Point’s western shore are relatively calm with lower tidal movement, allowing the sharks to conserve energy. “Say you’re a shark that has to swim to breathe, you want to choose a spot where you don’t have to fight against tidal currents … it’s like choosing to walk on a flat area rather than a hilly area,” she said. 

Other areas in the Nantucket Sound region and islands, by contrast, have such strong tidal currents that they appear to deter sharks from lingering, she said.

Water depth also matters. Off of Great Point, a narrow band of shallow water offers refuge from predators, while immediately nearby deeper waters provide quick access to feeding grounds. Larger shark species, like a white shark, is a known predator of sandbar sharks, making this balance between shelter and depth important.

Caroline describes the area as a “perfect storm of events” that draw the species back year after year: energy conservation, thermoregulation, predator avoidance, prey availability, and safety in numbers. 

Caroline also noted that as water temperatures continue to rise globally, southern species like spinner and blacktip sharks may venture further north into our waters. This has been documented with bull sharks in southern states. As a warm water species, water temperature is critical in delineating sandbar shark habitat and ranges. “We could also see sandbar sharks arriving earlier in the year and staying for longer periods of time if the water temperature supports their preferred temperature range,” Caroline said. This could have cascading effects on prey populations and predator-prey dynamics. Sandbar sharks typically eat fish — fluke, bluefish, and other bony fish species.

Sandbar sharks tend to steer clear of the Chatham and Cape area due to the congregation of white sharks there. 

Her conclusions are clear. Juvenile and adult sandbar sharks show strong dependency on this habitat. Nantucket is not simply a stopover, it is an annually used, ecologically important summer home.

What You Can Do

While sandbar sharks are not a threat to humans, awareness is key. Caroline emphasizes that understanding where and when sharks are most likely to be present allows beachgoers, swimmers, anglers, and surfers to make informed decisions. “Knowledge is very important,” she said. “These are wild animals, and I can’t control what they do, but if people know the patterns, they can decide how and where to safely enjoy the water.” 

You can also support ongoing research that helps monitor and protect these local sharks. Donations to the New England Aquarium’s Anderson Cabot Center for Ocean Life or the Nantucket Land and Water Council can be directed specifically to Caroline’s sandbar shark research. Every bit of support helps scientists continue to learn about these ecologically important predators and waters they call home.