Great white sharks surprise scientists in Great White North
An increase in shark tagging gives scientists clearer picture of elusive predators
A Halifax shark expert says scientists are surprised to learn there are more great white sharks showing up in Canadian waters than previously thought.
'We had no idea, no one had any idea this many great whites were coming up into Canadian waters.' - Steve Campana, Canadian Shark Research Lab
Steve Campana, head of the Canadian Shark Research Laboratory and a scientist at the Bedford Institute of Oceanography, credits an increase in tagging Atlantic populations of great white sharks.
“Up until last year, no one had a satellite tag, or a tag of any kind on a great white in the Atlantic,” said Campana.
He said though great white shark tagging has been successful in the Pacific Ocean and in the waters off South Africa, tagging the massive predators in the Atlantic has proved to be a challenge.
“Up until a year ago, I would have said, ‘No, we are seeing less [great whites] because they’re reported so rarely — even the commercial fishermen seldom catch them probably because they just bite through any gear they’re using. But there have been some increasing tags being applied to various sharks. And last year, for whatever reason, they were very successful in getting tags onto great white sharks down in American waters.”
There are two kinds of tags commonly used to tag sharks. The more common — a cheaper option — is the acoustic tag, which transmits signals to acoustic receivers which pick up the signals from the transmitters implanted in the sharks.
Six great whites with acoustic tags were detected earlier this year coming up off the Halifax line of acoustic receivers — the world's most extensive array of acoustic receivers spanning a distance of 185 kilometres offshore.
“Six. We had no idea, nobody in the world had any idea this many great whites were coming up into Canadian waters these days,” said Campana.
Another, more expensive, receiver is the satellite tag. These tags allow scientists to track sharks in real time, as opposed to acoustic tags, which record tracking data but must be retrieved in the field in order to download the information.
Great white shark off Newfoundland
Researchers have been tracking one such satellite-tagged great white shark they affectionately call Lydia. She measures 4.3 metres and is currently located about 20 to 30 kilometres off Placentia Bay in southern Newfoundland.
“Lydia is sporting a shiny new satellite tag on her dorsal fin — which is the fin sticking off of her back,” said Campana.
“This is a particular flavour of satellite tag known as a ‘spot tag’ … wherever the fin sticks out of the water in the sort of classic shark-swimming pose when you see the fin coming through the water … the satellite aerial … will transmit its location to a satellite and then down to the researchers. So we know whenever it breaks the surface, we know where that shark is.”
As for the reason Lydia is off the coast of Newfoundland, Campana said a shark that size is free to move as she pleases.
“It is an interesting situation. I was looking at the track of Lydia as she swam up from Florida where she was tagged back in March up to Newfoundland waters. I overlayed that with the satellite imagery showing the sea surface temperature and she apparently followed the edge of the Gulf stream up — which is a warm current of course,” he said.
Campana suspects Lydia is in Canadian waters, following food sources, but he said it’s really difficult to say..
“She’s probably just cruising around and looking for food,” he said.
“Seals are a very yummy delicacy to a great white shark."