Return of large marine mammals attracts some big jaws
By FRANK CARINI/ecoRI News staff
Depending on how you view “Jaws” — as a summer blockbuster or documentary — blame or thank the return of the gray seal to southern New England waters for attracting white sharks to our shores.
Greg Skomal, for one, is happy both species are here in greater numbers. The senior fisheries biologist with Massachusetts Marine Fisheries since 1987 and head of the Massachusetts Shark Research Program is one of the nation’s leading shark experts. He’s also a fan of the gray seal, and not just because they are bringing his preferred animal to study into the waters of the Atlantic.
Once great whites mature to 9 or 10 feet, they shift their diet away from fish to chubby marine mammals. Gray seals are a favorite prey of mature great white sharks.
“Great whites want the bacon of the seal,” Skomal said. “They want the fat, blubbery, buttery layer of the seals’ blubber. They don’t want the bones and meat.”
There’s plenty of fat to be had on these marine mammals, as portly gray seals can weigh up to 680 pounds. In the past four decades, the population of gray seals along the East Coast, most notably in the waters off Cape Cod and the Island, has rebounded, thanks to environmental protections.
Skomal gave a shark talk, sponsored by The Nature Conservancy, March 15 at the Barrington (R.I.) Public Library. He said white shark fishing interactions along the Eastern Seaboard are increasing, largely because of the return of gray seals after they were driven to the verge of extinction centuries ago.
Before 2004, great white sightings off the coast of New England were generally few, averaging less than two annually. But in the past few years, that number has increased significantly. A June 2014 study by the National Oceanic and Atmospheric Administration (NOAA), which Skomal helped write, found that the number of white sharks in the waters off the East Coast and Canada is growing.
The authors of the report attribute this resurgence to conservation efforts, such as a federal 1997 law that prevents the hunting of great whites, and the greater availability of gray seals.
Many of these seals are taking refuge on the shores of Muskeget, an island in Nantucket Sound between Martha’s Vineyard and Nantucket. They like the seclusion. Most of Rhode Island’s beaches, Skomal noted, have too much human activity for the seals' liking. He said gray seals like to rest onshore without being bothered.
“There’s a big pile of seals on Muskeget,” Skomal said. “And the great whites are coming in to take advantage of this collection of prey. It’s a pretty simple cause-and-effect model.”
White sharks are highly migratory animals, and most of the research being conducted on these apex predators is happening in South Africa, South Australia, Mexico and California — global hot spots for shark gatherings because of a buffet of seals and sea lions.
It was extremely difficult to study great whites in New England's coastal waters prior to the gray seals return. The sharks were here, or at least regularly passing through, but not hanging out in bunches.
“Until recently, there was little research being done in the Atlantic, because there were no large groupings of white sharks here,” Skomal said.
While the return of this predator-prey dynamic to local waters has led to better research opportunities, it also has brought white sharks closer to southern New England shores. Increased sightings of this fearsome creature have brought media attention, tourists and fear.
These sharks owe much of their chilling reputation — and exaggerated taste for human flesh — to a movie that was released 40 years ago this June. But attacks are rare, with only 106 unprovoked encounters — 13 of them fatal — in U.S. waters since 1916, according to University of Florida data.
Of the 500 species of sharks in the world, only a dozen — white, tiger, bull and hammerhead, to name a few — interact with humans, according to Skomal.
He said on the rare occasion that a great white attacks a swimmer or kayaker — as happened last September off the coast of Plymouth, Mass. — it’s likely a young, inexperienced shark just learning how to recognize and hunt big marine mammals.
“When a shark bites a human, he doesn’t want it — not fatty enough,” Skomal said. “Older experienced sharks are tuned in to the seals. They learn how to kill them. They go from a success rate of 20 to 30 percent to 60 to 70 percent.”
There are 40 tagged white sharks that regularly swim in the waters off Cape Cod, according to Skomal. Last summer, he and this research team identified 68 individual white sharks off the coast of Massachusetts — 43 males and 25 females.
Like snowflakes, no two whites look alike. Skomal said they all have different coloring patterns around the face, gills, tail and pelvic fin. White sharks also are a slow-growing, long-lived species. Skomal said they can live to be 70 years old.
As for the exact number of great whites swimming in southern New England’s waters, Skomal said researchers are just beginning to get an idea. He said tags are helping to answer many questions, including where these sharks go, noting that many travel up and down the Atlantic Coast from Nova Scotia to Florida.
By November, they are mostly gone from local waters and start returning again in May, according to Skomal.
Prior to the technological advancements of the past decade, most of Skomal’s research of white sharks here was conducted on dead sharks that had washed ashore or had been caught up in fishing gear.
"We were looking at a lot of dead animals," he said. You can learn a lot from a dead fish, but it doesn’t tell you a lot about behavior or movement.”
Among the white sharks the Skomal team has tagged include Internet sensation Lydia. The 16.5-foot-long, 3,086-pound female in her late 20s or early 30s has her own Twitter account, with more than 12,000 followers, and a dorsal-fin tracker. Since she was tagged two years ago, Lydia has traveled some 34,800 miles over the mid-Atlantic ridge toward Europe and western Africa and back.
On the OCEARCH website, the journeys of other sharks tagged by Skomal and his team can be followed. Katherine moves about Monomoy Island, Cape Cod Bay and Nantucket Sound. Julia, a 2,300-pound, 14-foot female tagged in 2011, regularly returns to the area on Memorial Day weekend.
In addition to the field work Skomal does as head of the Massachusetts Shark Research Program, which studies the ecology, distribution and relative abundance of sharks in local waters, a big part of his job is to educate the public about sharks.
The southern Connecticut native and University of Rhode Island graduate also is an adjunct faculty member at the University of Massachusetts School of Marine Science and Technology in New Bedford, Mass., and collaborates with the Woods Hole Oceanographic Institution.
Skomal also has appeared in film and TV documentaries about sharks, including the Discovery Channel’s “Shark Week” and “Jaws Comes Home,” which featured Skomal investigating the reasons behind the return of white sharks to Cape Cod.
The Atlantic White Shark Conservancy funds much of his research.