Predator-Prey Relationship Key To Understanding White Sharks, Says Skomal

By: Kat Szmit

Topics: Marine Mammals , Sharks , Chatham , Beaches , Summer residents , seals

Shark scientist Greg Skomal discusses the findings of years of research he's conducted on white sharks during a talk at the Museum of Natural History on Sept. 26. Kat Szmit Photo

BREWSTER – When it comes to living with white sharks, there are many options: stay out of the water, move inland, or, if you're Greg Skomal, a marine biologist with the state Division of Marine Fisheries, you do all that you can to learn as much as you can about the creatures, and ideally save a life or two in the process.

Skomal has been doing just that—studying everything possible about white sharks—for more than a decade, and on Sept. 26 shared some of what he's learned in a talk on “Living With White Sharks” at the Cape Cod Museum of Natural History in Brewster.

When Skomal's studies began, white sharks were a rarity on Cape Cod, not nearly as concentrated as they are now. But through research, which has included necropsies, tagging, and sifting through mountains of data, Skomal and fellow scientists, with the support of the Atlantic White Shark Conservancy, have made progress toward understanding what makes white sharks unique and impressive. But, as Skomal told the sold-out audience last week, there is more to be done, starting with taking a much closer look at the relationship between predator and prey, in this case sharks and seals.

“We need to drill deeper and use new technologies to figure out this relationship better,” Skomal said. “As the seals stay close to the shore, the sharks get closer and closer. When you have this overlap between predator and prey, you have…bites, shark attacks, fatalities.”

Using a slideshow punctuated with at times graphic video footage of shark-on-seal predations, tagging, and even breaches, Skomal gave an overview of what he and his fellow scientists have been doing since first turning their attentions to studying white sharks in 2009.

In the beginning, when sharks along the Cape were rare, the main method of study came through necropsies.

“[I would] get up to my elbows in blood to learn what I can from that animal, not only to figure out why it might have died, but also to get tissue samples to get information,” Skomal said, noting that during a necropsy a shark is “methodically taken apart” with the various parts sent to labs for testing.

Though his white shark studies didn't sharpen until the late 2000s, it was a thrill when a white shark trapped itself in a salt pond on the Cape, sticking around for two weeks. While it was in the pond, Skomal was able to affix one of the first $4,000 tags...which fell off not 45 minutes after the shark made its way out of the salt pond.

“That’s the worst possible timing,” Skomal joked. “Had it been one day later I’d have had one day of data.”

In 2014 Skomal embarked on a five-year population study, during which he and crews of shark experts, with the aerial assistance of spotter pilot Wayne Davis, would track down white sharks, film them with GoPro cameras on long poles, and affix tags to their dorsal fins. Since then Skomal and his crew have affixed sharks with 182 acoustic tags, 55 pop-up satellite tags, and eight real-time satellite tags. Each of the different tags have not only given them thousands upon thousands of bits of data to pore over regarding the white shark population, but also where they like to go while visiting the Cape.

In 2019 Skomal turned the attention toward Cape Cod Bay.

“There are white sharks in Cape Cod Bay,” he said. “What’s interesting about what we’ve seen so far, 100 percent of the sharks we’ve seen so far have been offshore, not on the beaches like we see on the Outer Cape.”

Skomal said those sharks are likely targeting fish as they aren't moving close to the beaches to the extent that they do on the Outer Cape where the seal population is highest.

Using the various tags, particularly the acoustic tags with receivers all along the Massachusetts coastline, has allowed Skomal and his team to get a better sense of where the white sharks are spending their time. Most prefer the Outer Cape area.

“They’re spending time where the seals are in greatest abundance,” said Skomal. “We’re working with all these towns on the South Coast, and now we can tell them on a relative scale where the sharks are.”

But the data offered by the tags is often past tense. Skomal wants to know what's happening with sharks now. This season saw testing at Head of the Meadow Beach of technologies that would allow immediate transmission of data, including the presence of a tagged shark, which offered key insights, but Skomal said the problem is that not every shark is tagged.

“None of the technologies are 100 percent foolproof,” he said. “It's only detecting the tagged one and isn't telling you when there's an un-tagged shark there.”

Plans are now in the works to expand acoustic research to determine how sharks are behaving close to shore.

“We want to know how the white sharks are utilizing this underwater habitat to figure out how sharks are getting at these seals,” Skomal said. “If we can figure out how sharks utilize channels, sandbars, underwater topography, we can then expand that to the whole of Cape Cod and see what species might be more vulnerable to shark attacks.”

Skomal said ideally, factors such as those previously mentioned, as well as tides, moon phases, and storm impact will be taken into consideration and will help paint a clearer picture of when sharks pose a greater threat along our shores.

Culling seals, which total more than a half a million in the Northeast, Skomal said, is not an answer.

“In terms of the sheer numbers you’d have to remove to make it safer…,” Skomal said. “A lot of people don’t understand the dynamics of the seals. They’re all part of one population that’s forever moving. To reduce to a level where you don’t see them, you’d have to really reduce that half a million. I just don’t know how you would achieve it.”

New technologies, including accelerometry, are also being employed, which allow scientists to study pitch, roll, altitude, water temperature, and activity every second. Plus, these tags have cameras that offer a shark point of view.

“You can look at what this animal is doing in three-dimensional space every second,” Skomal said.

The hope is that all of the combined data will allow the prediction of where predatory events are most likely to happen and when, which, ideally, will keep beachgoers safe.

What Skomal tries not to do is affix tags that require taking sharks out of the water, as he feels they're detrimental to the work he's doing.

“You don't want to modify the behavior of the animal you're trying to study,” he said.

And those animals, Skomal said, are as individual in their behaviors as humans.

“With white sharks, there are far more individual strategies than I ever thought we'd see,” he said. “We've gotten to know some of these sharks quite well. They're creatures of habit [with] remarkable variation among individuals that I find fascinating.”

So what can people do while waiting for technology to catch up? Be smart, be safe, and if you're really afraid, stay out of the water.

“This is nature,” Skomal said. “Wild nature.”