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Great white sharks: They'll be back



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State marine biologist Greg Skomal, speaking at a press conference yesterday at the New England Aquarium in Boston, said he was surprised to see the great white sharks "pop up off Florida."Cape Cod Times/Steve Heaslip



By Doug Fraser

dfraser@capecodonline.com

March 04, 2010

BOSTON — Since applying satellite tags to five great white sharks off Chatham last summer, shark researcher Greg Skomal has been anticipating their return to Cape waters this year. But he's surprised with the migratory data that is being gathered from the tagging effort.
If he were a betting man, Skomal would have put money on the likelihood that the sharks headed east, far offshore for the winter like blue sharks and basking sharks do, and following the behavior of great whites studied on the West Coast.
"I was kind of surprised to see them pop up off Florida," said Skomal, speaking yesterday at a press conference at the New England Aquarium. Three of the five satellite tags, one in January, one in February, and another just a few days ago, released themselves at programmed intervals from their shark hosts, then floated up to the surface off Jacksonville. The tags transmitted data on depth, water temperature, and light levels to satellites, which relayed the information to researchers. The last two tags are scheduled to pop off over the next two months.
Primarily using light levels to determine the elevation of the sun, Skomal, a marine biologist with the state Division of Marine Fisheries, and his staff were able to re-create the migration of two of the three sharks over the past five or six months. Data on the third was still being downloaded from the satellite yesterday.
Skomal said he was surprised to find that, after lingering through September in waters just off the Cape, the sharks made a beeline for Florida, traveling at 1 to 2½ mph, following the edge of the continental shelf, constantly diving down 100 to 150 feet to the bottom.
"They are probably motivated by feeding (in making these dives)," Skomal said.
While the sharks sometimes ventured into water that was as cold as 45 degrees and as warm as 81 degrees, they spent 80 percent of their time in water between 59 and 73 degrees.
One exception was a period of 10 days in early November in the Gulf Stream off North Carolina, where one of the sharks dove down to 1,500 feet to 44-degree water. The two sharks with completed data analysis remained in waters 50 to 80 miles off the Jacksonville coastline through December and January, and may still be there, Skomal said.


"What we may be seeing is a seasonal feeding grounds," he added.
What won't surprise Skomal would be if the tag, due to be released in May, shows that shark making its way back up the coast toward the Cape. Decades of studies on great whites in the Pacific Ocean have shown they have tremendous fidelity to specific seal colonies, returning year after year. Skomal is anticipating their return to Chatham and the large seal colony on Monomoy Island, which has grown from near zero to numbering in the thousands in recent years.
What researchers don't know are how many great white sharks there are, both in local waters in the summer, and along the East Coast. That number could be important since great whites generally don't feed for a month after dining on a seal, Skomal said.
Researchers will be tagging great whites again this summer thanks, in part, to a private donation of $25,000 DMF executive director Paul Diodati announced at yesterday's press conference. Airplane surveys last summer showed sharks patrolling away from the seal colony as far north as Wellfleet, and aerial photographs showed sharks close to seals in the surf, in fairly shallow water. Skomal hopes to work with towns that might give researchers some warning if sharks are around.
As to when these migrants return to the Cape, just keep an eye on the water temperature.
"They like it around 60 degrees," Skomal said