'Big and powerful' shark attack left ocean glider adrift off Nova Scotia for days

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A close-up of the rudder and thruster shows the damage incurred after a Sunday shark attack. (Paul Poirier/CBC - image credit)
A close-up of the rudder and thruster shows the damage incurred after a Sunday shark attack. (Paul Poirier/CBC - image credit)

An autonomous ocean glider was disabled by a shark attack Sunday night near Sable Island, abruptly ending a scientific mission and putting the vehicle out of service for months.

The wave glider was 200 kilometres off the coast of Nova Scotia listening for tagged halibut.

"We lost communication with the rudder module, so we were no longer able to steer the glider, so it was drifting freely," said Richard Davis, manager of the glider group at Dalhousie University. "But we still had communication with it. We knew where it was all the time."

An emergency 76-hour effort was undertaken to retrieve the glider which revealed teeth marks and punctures all over what is called the "thrudder," a combination thruster and rudder.

The glider was returned to a Dalhousie facility on the Dartmouth waterfront. Fred Whoriskey of the Ocean Tracking Network examined the bite marks and swabbed the damaged area for environmental DNA traces in an attempt to "figure out who the culprit is of this particular attack on this innocent autonomous vehicle."

"It must have been a pretty big and powerful shark because it managed to penetrate three millimetres or more with teeth marks into the aluminum base of what's solid aluminum," said Whoriskey.

Identifying the culprit

He said the shape of the bite marks rules out a porbeagle. He thinks it was most likely a mako or great white shark because they're regularly in the area.

Whoriskey said it might even be a tiger shark, which is cold-blooded. He said they tend to come up later in the summer when the water has warmed up.

It's unclear what prompted the attack. Noise from the propellers or electronic signals may have attracted and irritated the shark. It could have been a taste test to see if the glider was food.

"The third possibility is if you look at the colour of the machine, this is what in the industry they call yum yum yellow," said Whoriskey. "It is a high-contrast thing and can tend to excite an attack under some circumstances."

Fix will cost about $25K

The attack has put the glider out of service until a new rudder system can be secured, which will likely cost around $25,000, said Davis.

"It's a pretty big deal," he said. "I don't budget for that. We do have a contingency fund, but it's not small change."

Whoriskey hopes the glider will return to the water this year, but said the COVID-19 pandemic has slowed down getting equipment from suppliers.

Why the glider was in the water

The damaged wave glider belongs to Environment and Climate Change Canada and is on long-term loan to Dalhousie University.

It was deployed about three weeks ago near a large underwater canyon known as the Gully as part of a project to monitor the movements of Atlantic halibut tagged by DFO earlier in the year.

It was also measuring meteorological and oceanographic conditions, and sending that data back to shore in real time for use in weather forecasts and climate modelling.

Paul Poirier/CBC
Paul Poirier/CBC

Davis said he believes there have been more gliders in the Atlantic Ocean this year than ever before, meaning more shark strikes are possible.

"If we do start to see a pickup, we're going to have to find some mediation strategies as to how to reduce this kind of thing, because a valuable mission was truncated ... but what those measures are at this point, I don't know," said Whoriskey.

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