Abundant shark population off Cape surprises researchers

ORLEANS — With a quick jab, Greg Skomal reached a milestone last week. The detachable stainless steel tip on his harpoon penetrated the skin of a 14-foot male great white shark hunting seals just 20 feet off Nauset Beach. The dart lodged between the tendons at the base of the shark’s dorsal fin, tethered to a pencil-size acoustic tag that will broadcast a signal identifying the shark for the next decade.

Skomal had tagged his 100th great white, dating back to 2009 when the massive predators began showing up in appreciable numbers off Chatham. He named the shark Casey after shark tagging pioneer Jack Casey, who founded the National Marine Fisheries Service Cooperative Shark Tagging Program in 1962 and developed many of the techniques still in use today.

As the number of sharks coming to the Cape seems to grow every year, so has Skomal’s appreciation of the unique situation he finds himself in: a shark researcher caught in a real-life "Sharknado."

“If you told me 10 years ago we’d hit a hundred, I’d say, 'You’re crazy,'” he said.

The number of sharks ranging along the Cape’s shoreline, many passing near surfers and swimmers, is sobering. Skomal, a senior fisheries biologist with the state Division of Marine Fisheries, is finishing the third year of a five-year population study and has identified more than 200 individual sharks through tagging and underwater videos that find unique scars and coloration on each animal.

“Frankly, I was surprised nobody got bit this summer,” said Chris Lowe, a professor at California State University, Long Beach, noting that seals and sharks have modified their behavior to the point where the sharks must hunt in increasingly shallow waters, including the popular beaches where millions swim every summer.

A soon-to-be published study of seven adult gray seals, captured and tagged on the Cape three years ago by a team led by Duke University professor David Johnston, showed them leaving the shore to feed at all times of day and night, and taking multiday trips, when sharks are not around in the winter. But the summer is a different story. Johnston said the study found seals have adapted their behavior to better avoid white sharks. Since great whites rely heavily on their eyesight to hunt, tagged seals were leaving at twilight and taking only single day trips in summer, he said.

“They spent their days close to shore and hauled out,” Johnston said.

That put them close to humans, who also enjoy the beach during the day.

Lowe oversees the Cal State Long Beach Shark Lab, which uses acoustic tags to track great whites.

Before he moved to California to do shark research, Lowe spent his formative years on Martha’s Vineyard.

“I grew up there, and did a lot of fishing around the Cape and Vineyard, and never saw a gray seal or a white shark,” he said.

That changed in the late '80s, early '90s, as conservation measures such as the Marine Mammal Protection Act bore fruit. Gray seals started showing up in Cape and Islands waters and started pupping. Now the population is booming, numbering in the tens of thousands. By the mid-1990s great whites were also a federally protected species.

When a 14-foot female great white named Gretel became trapped in a small lagoon on Naushon Island in 2004, it was apparent that these heretofore rarely seen predators were now frequenting the Cape’s shallow coastal waters.

Inhabiting the top of the ocean food chain, great whites naturally have relatively low abundance, a slow population growth rate and are the most sensitive to ecosystem changes. The abundance of seals and the return of white sharks are good indicators that the ocean remains productive despite overfishing and climate change, Lowe said.

“You can’t have the seal population expanding unless there is food for them,” he said. “I have a hard time looking at the whole system and not seeing ecosystem recovery.”

Lowe oversees the Cal State Long Beach Shark Lab, which uses acoustic tags to track great whites.

Before he moved to California to do shark research, Lowe spent his formative years on Martha’s Vineyard.

“I grew up there, and did a lot of fishing around the Cape and Vineyard, and never saw a gray seal or a white shark,” he said.

That changed in the late '80s, early '90s, as conservation measures such as the Marine Mammal Protection Act bore fruit. Gray seals started showing up in Cape and Islands waters and started pupping. Now the population is booming, numbering in the tens of thousands. By the mid-1990s great whites were also a federally protected species.

When a 14-foot female great white named Gretel became trapped in a small lagoon on Naushon Island in 2004, it was apparent that these heretofore rarely seen predators were now frequenting the Cape’s shallow coastal waters.

Inhabiting the top of the ocean food chain, great whites naturally have relatively low abundance, a slow population growth rate and are the most sensitive to ecosystem changes. The abundance of seals and the return of white sharks are good indicators that the ocean remains productive despite overfishing and climate change, Lowe said.

“You can’t have the seal population expanding unless there is food for them,” he said. “I have a hard time looking at the whole system and not seeing ecosystem recovery.”