They’re here. Once rare in this area, great white sharks—hundreds of them—prowl the shallows off Massachusetts’ Cape Cod beaches. The resurgence of the past decade has surprised just about everyone, including marine scientists. Noted shark expert Greg Skomal, who has studied white sharks off New England since the early 1980s, says he didn’t see one anywhere near Cape Cod until 2004, and he didn’t tag his first one there until 2009 .
A new study shows that the eastern coastline of this peninsula now hosts one of the largest seasonal white shark gatherings in the world and is the first documented hot spot in the North Atlantic. Cape Cod joins established hotspots in South Africa, central California, Mexico’s Guadalupe Island and Australia’s Neptune Islands. The sharks are most concentrated in Massachusetts from June to October, the same time of year when more than three million vacationers regularly flock to the cape.
The implications for public safety are obvious. The sharks hunt in the swell along some 40 miles of beach managed by the Cape Cod National Seashore. Leslie Reynolds, the organization’s deputy superintendent, says 2012 was the first time a shark injured a person along this beach area. Two incidents followed, including a deadly encounter in 2018. While there have been no attacks since then, the danger is always there. A task force convened by Reynolds that includes municipal beach safety directors, along with representatives from the Massachusetts Department of Marine Fisheries and The Atlantic White Shark Conservancy, has implemented safety measures such as new beach signs, a flag warning system, training on how to stop the bleeding of a victim, and public outreach and education about shark threats. Called an iPhone app Sharkivity gives the latest observations.
Shark protection brought in white shark experts from other parts of the world to advise the safety planners. “Understanding the trends, movements and behavior of shark populations is critical to shark safety and conservation,” said Alison Kock, a marine biologist for the South African National Parks, who visited Cape Cod in 2016.
Sharks are congregating on the cape as gray seal populations rebound there, experts say. The seals had been wiped out from New England in the early 1960s, largely due to culling by commercial fishermen. The Marine Mammal Protection Act of 1972 made it safe for the seals to return from Canadian waters, but it wasn’t until the early 1990s that they established colonies. With no natural predators and plenty of fish to eat, the seals thrived. According to one estimate, there were more than 30,000 seals on the cape in 2017. The sharks were probably drawn to them by scent trails. Seals are a favorite high-fat prey for white sharks as the fish make their annual northward migration.
White sharks are also protected. The U.S. government designated them a “prohibited species” in 1997, making it illegal to catch the sharks between three and 200 nautical miles out to sea. Massachusetts followed suit in 2005, banning fishing between shore and three miles offshore.
Many environmentalists consider what is happening on Cape Cod to be a conservation success story. Public safety concerns about both seals and sharks could have led to draconian measures, such as culling, but instead nature was left to fend for itself. “What we’re seeing in Cape Cod is a recovery of the trophic (food) web and what it was like before the overfishing and slaughter of many of the animals at the top of the food chain,” said Chris Lowe, director of the Shark Lab. California State University, Long Beach.
![Called a tagged shark](https://static.scientificamerican.com/sciam/assets/Image/articles/inline%20photo2_shark%20and%20boat_3_AWSC%20Aug%2015_2023_6.jpg)
As the number of white shark sightings increased in the early 2010s, people ranging from National Park officials to leaders of conservation organizations to Cape residents wanted to know just how big the population was getting. That led to a four-year study with Skomal, a senior fisheries biologist at Massachusetts’s Division of Marine Fisheries. The researchers estimate that about 800 individual white sharks visited the sampling area between 2015 and 2018.
Over the past decade, population studies have been conducted on white shark hotspots along California’s central coast, in South Africa, and on Guadalupe Island; the estimated populations were 300, 908, and 78, respectively. Like those studies, the Cape Cod Project identified sharks by their unique coloration and dorsal fin profiles. But the other studies all used bait or artificial attractants to lure sharks onto a research vessel for observation. Sharks willing to approach a boat are likely a subgroup of all sharks in the area, and this creates uncertainty in the data.
“No decoys or bait were used to attract sharks” in the Cape Cod study, said Megan Winton, principal investigator and staff scientist at the Protection of Atlantic white sharks, the non-profit organization that provided most of the research funding. “Instead, we relied on a scout plane to find free-swimming sharks and radioed their locations to a research vessel.” Aleutian dream. “Once we found a shark, we shot underwater videos with a GoPro camera attached to a fiberglass painter’s stick.” The sheer amount of data collected also sets the study apart: The researchers conducted 137 survey trips, encountered sharks 2,295 times, and collected a total of 2,803 videos.
But does the Cape Cod shark population represent an increase in the overall North Atlantic population? It’s hard to know. Those sharks were elsewhere before they visited the cape. “Just because we see them or don’t see them doesn’t mean their numbers have changed,” said Taylor Chapple, an assistant professor in Oregon State University’s marine, fisheries, and wildlife department who was involved in the central California Studies. “It could just mean that their behavior or distribution has changed or our ability to find them has changed.”
Skomal agrees, but adds, “Our population estimates increased with each year of our study. This overall trend points to a growing population, at least on Cape Cod and possibly beyond.”
The research has raised other questions. Is the Cape Cod shark population still growing? What consequences would this have for the seal population? What is the size of the wider Northwest Atlantic white shark population?
To find answers, the Cape Cod research team is studying predator-prey relationships, the small movement of sharks near the coast and other phenomena that will provide further insight into the biology, ecology and natural history of the species. Like John King, captain of the Aleutian dreamsays, “The population study is just the end of the beginning.”