Friends of Winthrop Beach presented “Shark Talk with Doctor Gregory Skomal” on May 9 at the Neil Shapiro Performing Arts Center at Winthrop High School with the hope of inspiring youth to further their education in marine biology, oceanography, and the protection of sharks.
Skomal is an underwater explorer, photographer, aquarist, and author who has been actively studying sharks since 1989. The shark expert discussed the advanced research tools used to track the movements of the Western North Atlantic white shark population off the shores of Cape Cod: its prime habitat due to the aggregation of grey seals – their main prey.
“I’ve seen such an advancement in the technology that has allowed us to get insight into how these animals live,” said Skomal, marine biologist, Massachusetts Division of Marine Fisheries. “For many years, we thought of them as rare event species, a term used by scientists to talk about an animal we don’t see a lot of. If you don’t see a lot of it, fishermen don’t encounter it frequently, and you don’t know much about the biology, ecology, behavior, or any aspect of that species. For hundreds of years, we have lagged behind in the Atlantic because we could not predictably find white sharks and study them.”
Western North Atlantic white sharks — which can grow up to 19-feet-long and live an excess of 70-years — occur from the Gulf of Mexico to Canada, and have appeared as far north as Newfoundland; but the pioneer research into their basic biology was conducted in Cape Cod by Doctor Frank Carey, of the Woods Hole Oceanographic Institution in the 1970s-early 1980s. Then, white sharks were overly exploited by recreational and commercial fishing; and the seal population was decimated nearly to extinction.
In 1979, while witnessing a white shark feeding on a whale carcass, Carey inserted an acoustic tag to record the animal’s behavior. The three-and-a-half-day glimpse into the biology of the white shark was the first of its kind.
“A short track by today’s standards; but in those days, it was riveting and a landmark paper on a global scale,” exclaimed Skomal. “What I thought was really cool about this is he was also able to tell where the shark was on the water’s continental shelf.”
Those studies had remained the only research scientists knew about the behavior of white sharks until Skomal and his associates began their work in 2009.
Skomal believes that as a result of the U.S. government’s 1997 designation of the white shark as a prohibited species, its population has been rebounding. Additionally, since the Marine Mammal Protection Act of 1972 afforded marine mammals the highest level of protection, seals have begun to recolonize.
“We’re not seeing more white sharks because of climate change; we’re seeing more white sharks because of seals,” Skomal clarified. “White sharks are one of the only species that can affectively attack and kill pinnipeds, a term for seals and sea lions. Where there are breeding colonies and big haul-outs, white sharks will go to those areas at different times of the year, when environmental conditions are ideal to target and feed. Seals are a rich source of energy.”
In 2004, Skomal sensed that white sharks were predictably returning to Cape Cod when a 13-foot-long female spent two weeks in an estuary in the Elizabeth Islands, south of Woods Hole. He inserted a sophisticated satellite tag upon meeting her. Over the course of a half-a-dozen years, Skomal has witnessed the reappearance of more white sharks.
“In the time those two species were gone, Cape Cod evolved from an agricultural community to a more tourist-based economy. Water activities – from surfing, kayaking, paddleboarding, and scuba diving – became very popular,” described Skomal. “When you re-establish a top predator feeding on its natural prey, which sometimes looks like people, you get potential for negative interactions between sharks and people.”
Up until a series of fatal events, Skomal’s studies concentrated on the sharks’ large-scale movements using satellite and acoustic technology. He began focusing on collecting information that could enhance public safety and help swimmers, beach management, and lifeguards become more aware of the presence of sharks.
“There is a lot of anxiety on Cape Cod because of these animals,” Skomal acknowledged. “We assume when sharks bite humans, they’re making a mistake. If it was intentional, they would consume the person; and they very rarely – if ever—consume the person. It’s good news in that they are not targeting people. They’re targeting what they perceive as their natural prey, which is seals. If we know when they’re trying to feed, where they’re trying to feed, and how they feed on seals, then we can perhaps advise the public. This is an ambitious project. The ultimate goal is to advance public safety.”
Skomal explained the tools he uses to understand the sharks’ patterns: acoustic telemetry, broad and fine-scale arrays, wide receivers, satellite technology, and behavior tags.
“This is the latest and greatest technology, as far as I’m concerned. They’re camera systems that we’re mounting on fish,” expressed Skomal. “Drone technology has really taken off, as well. Observing the animals from the air is another, too. I want to know what they do every minute to minute; second to second.”
Instead of chumming to draw the sharks in to capture and tag, Skomal and his team travel to the sharks directly. Once pilot, Wayne Davis, spots a shark from the air, he notifies Skomal. From the bow pulpit of a boat, Skomal uses a long tagging pole to insert a small, intermuscular dart into the base of a free-swimming shark’s dorsal fin. The tag is tethered to an acoustic transmitter, which emits a high-frequency of 69 kilohertz. When a fixed receiver detects a shark over a range of 500 yards, it logs the time, date, and shark identification. These acoustic tags last some 10 years.
“What I’m not trying to do is handle, catch, and hook the shark, or do anything that’s going to change its behavior,” explained Skomal, who showed footage of a white shark tagging sequence. “We set up an array of acoustic receivers all around Massachusetts to get a sense of where the sharks spend their time.”
The same method is used to attach satellite tags, which record temperature, depth, and light levels every 10 seconds. They can be programmed for up to a year and will float to the water’s surface.
“The data we’ve collected from our tags has blown up into over a million data points from our sharks that show these animals are not only coastal; but also have an oceanic phased,” Skomal emphasized. “When they go into the Atlantic, they dive into depths of 3,000 feet every day; and there is no scientist who can tell you why.”
Although sharks emerge throughout the coast of Massachusetts, Skomal and his team tag sharks primarily along the outer Cape. They typically haul receivers into the water at the end of May, and will remove them in January or February.
Based on collected figures, scientists can examine the frequency of predatory events, when they are occurring over the course of a day or night, and recreate the three-dimensional movements of the shark.
“Their presence is really driven by water temperature. Once we drop below 50 degrees, they’re moving out of here,” said Skomal, who has catalogued over 700 individual sharks in Massachusetts.
“I work closely with almost every harbormaster in Massachusetts to try to get a receiver in their waters,” revealed Skomal. “My agency has receivers off Boston, Salem, and Cape Ann; and works with harbormasters from Hingham to Plymouth, and around Cape Cod.”
Skomal noted the peak months of August, September, and October, when there are an abundance of seals and temperatures are optimal. Tagging data reveals that the highest number of white sharks congregate on the outer Cape from Provincetown to Monomoy, and on the eastern side of Cape Cod Bay, where they capture their prey.
“You would think that because I’m on the water 30-40 times a year off Cape Cod that I’d see this every day; but over the course of 15 years, I’ve only seen it about 30 times,” Skomal pointed out. “When we get one of those rare observations of a shark successfully feeding on a seal, we’ll try to videotape the shark consuming the seal, and get information on the depth, temperature, size of the shark, the nature of the seal, which species of seal, and the size of the seal.”
White sharks are ambush predators that spend a considerable amount of time lingering between deep sand bars. They can accelerate up to 15-miles-an-hour while in pursuit of seals.
“Know what your beaches look like low and high tide,” advised Skomal. “Know the sandbar system, and deep troughs, and use that information to inform the public.”