Two great white sharks spent last summer off Nova Scotia searching for grey seals either around or migrating from Sable Island, according to new research from Canadian scientists trying to figure out where the endangered predator lives when in Canadian waters.
"The significance is, it led us to new hypotheses on why they are here," said biologist Heather Bowlby, research lead for the Canadian Atlantic Shark Research Laboratory at the Bedford Institute of Oceanography in the Halifax region.
The Department of Fisheries and Oceans has tagged two great white sharks with satellite tracking devices in an effort to identify "critical habitat" in Canada where the fish are listed as an endangered species at risk.
One great white shark was a female tagged off Cape Cod.
The other was a young male tagged last summer off Port Mouton on Nova Scotia's South Shore.
That male was the first great white tagged in Canada.
Behaviour indicates seal hunting
Both sharks displayed similar behaviour while on the Scotian Shelf last summer.
They stayed exclusively in the top 50 metres of the water column and travelled in what appears to be a search pattern to intercept grey seals moving from the huge colony on Sable Island to areas where seals come ashore in Nova Scotia and elsewhere on the Eastern Seaboard.
"We were surprised that there was such good evidence of predation up here. We could see that areas we'd expect to be important to seals were also where we were seeing the searching behavior of white sharks and that they were staying so high in the water column," said Bowlby.
"If you think of juvenile grey seals that would be foraging along the coastal waters off Nova Scotia they would have to come to the surface to breathe air. They would stay in the top portion of the water column similar to other marine mammals and also some of the larger pelagic fish like tunas."
The tags reveal the sharks tracking back and forth off Nova Scotia, ranging progressively farther and habitually returning to the same locations, in one case just south of Sable Island and others off southern Nova Scotia.
Well over a hundred great whites have been tagged off Cape Cod with acoustic or satellite tracking devices.
Of those, four white sharks came to Nova Scotia last year, Bowlby said.
"It's not to suggest that only four animals came to Canada or that that's an actual number but say if there were 2,000 animals in the U.S. and you expect five per cent here, its in the tens of animals rather than in the thousands."
Port Mouton gets most great white shark acoustic hits
Bowlby said most are likely repeat visitors who have learned there is food here.
To put the numbers in perspective, it took DFO three days to find the great white off Port Mouton and three hours to find 15 off Cape Cod, albeit with a spotter plane.
"We are talking low numbers," she said.
In addition to the satellite tags, DFO has listening posts on the ocean floor along the coast of Nova Scotia.
They are located off Scaterie Island Cape Breton, the Eastern Shore — under consideration as a marine protected area, St. Margarets Bay, Mahone Bay and Seal Island off Yarmouth.
Bowlby said Port Mouton, which sees a lot of seals coming ashore, gets the most "pings."
Tuna fishermen have also reported great white sightings in the area.
DFO plans to look again in 2019 to tag more great white sharks off Nova Scotia.
Not affiliated with Ocearch
Bowlby's research is not connected to the Ocearch shark research program.
The U.S.-based organisation sent its research vessel to Nova Scotia for the first time in 2018, where it also tagged great white sharks.
Ocearch hooks great whites and pulls them on board for tagging, a practice shunned by researchers at the Massachusetts Division of Marine Fisheries which has pinned acoustic monitors on dozens of great whites.
DFO did not pull the sharks from the water that it tagged. It has not taken a public position on the practices used by Ocearch.
Ocearch raised hackles last September when it chummed the waters near Hirtles Beach in Lunenburg.
About the Author
Paul Withers is an award-winning journalist whose career started in the 1970s as a cartoonist. He has been covering Nova Scotia politics for more than 20 years.
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