Ocean floor listening posts reveal secrets of blue whales

Underwater recorders attached to the ocean floor are revealing new information about endangered blue whales off the coast of Atlantic Canada.

It turns out the biggest animals on the planet — and the loudest — are present year round.

"Blue whales are using our waters off Nova Scotia more than I expected them to be," said Hilary Moors-Murphy, a research scientist with Fisheries and Oceans Canada.

Moors-Murphy is lead author of a new study on the distribution of blue whales off Eastern Canada and outside the Gulf of St. Lawrence.

Listening posts 1,500 metres deep

She credits the use of year-round underwater recorders capable of capturing the four distinct calls made by the North Atlantic population of blue whales.

Their booming, low-frequency calls can travel 100 kilometres or more.

"The use of the technology is really important because it has revealed new information on whale occurrence in Canadian waters. In the case of blue whales, we did think that most of the individuals migrated down south during the winter, but the acoustics have revealed that at least some individuals are remaining through the year," Moors-Murphy said.

Recorders have proved useful in winter when sightings are infrequent because of wind and waves.

"It is very interesting that our peak call rates in some of those areas occur in the winter months. So this is something that's relatively new," she said.

Top blue whale habitats

The report identifies five top habitats most likely to be important to the north Atlantic's blue whale population, which is estimated at just a few hundred individuals.

They are:

• Deep-water areas off the continental slope of the Scotian Shelf. 
• Deep-water areas off the continental shelf of the Grand Banks.
• The Laurentian Channel, between Cape Breton and Newfoundland and Labrador.

The study also says the southwest coast of Newfoundland — scene of several fatal ice entrapments — and shallower areas on the western Scotian Shelf are also potentially important habitats.

The mystery remains

Exactly how and why blue whales use these areas is unknown, the report says.

Hal Whitehead, an oceanographer at Dalhousie University, has recorded blue whale sightings for decades during his research of mammals in the underwater canyons near Sable Island off Nova Scotia.

He has also participated in the acoustic monitoring programs.

The sight of a 25-metre blue whale surfacing has lost none of its lustre.

"They're extraordinarily impressive. Wonderful to see. I always enjoy it very much. And it doesn't happen very often."

For him, they remain an enigma.

"A whale which should be so present because it's both huge and has an incredibly large sound, and yet we don't see them or hear them all that much. And we're not sure where they are most of the time," Whitehead said.

Potential conflict with man-made seismic activity

Whitehead said what is known is that whales are at risk from man-made seismic activity — when large underwater guns are fired into the ocean to reveal the presence of hydrocarbons under the ocean floor.

The explosive bangs can disrupt feeding, he said.

The noise can travel into marine protected areas, like the Gully, the big underwater canyon near Sable Island declared off-limits to exploration when it was designated as Canada's first marine protected area in 2004.

"We're getting increasing evidence that blue whales and their relatives are affected by these sounds," he said.

Whales present in offshore energy-lease areas

The new DFO study notes the potential overlap.

"Oil and gas lease areas off Eastern Canada are concentrated in the same regions as highly and moderately suitable habitat for blue whales: along the deep water of the continental slope. Frequent and large-scale seismic survey efforts occur in these areas," the report said.

Moors-Murphy said seismic guns are only one source of noise.

"Things like shipping noise, noise produced from even fishing activities or military activities, oil and gas exploration and drilling, those are all a concern for whales in general in our water and blue whales as well," she said.

Ice entrapment

While seismic activity is a source of concern, ice entrapment off the southwest coast of Newfoundland is a confirmed killer of blue whales.

Forty have died since 1974.

In 2014, at least nine adult blue whales were entrapped and killed by moving sea ice — a significant loss to the small population of adults.

"This highlights the southwest coast of Newfoundland as both a consistent area of spring occupancy by blue whales, and an area of significant mortality risk for the endangered northwest Atlantic population,' the report said.

Regardless of the cause, Moors-Murphy said, offshore deaths are likely going unnoticed.

More listening posts in 2019

It will likely be years before scientists are able to predict the number of blue whales in the North Atlantic.

Moors-Murphy says this study is a good start. It pulled together data going back to the 1960s, when blue whales were still hunted on the East Coast of Canada, and included sightings made during aerial surveys covering tens of thousands of kilometres of ocean.

And more data is coming in from the acoustic recorders — some of which were installed in response to the crisis involving the deaths of North Atlantic right whales.

In 2019 scientists will be listening to recorders attached to the ocean floor at locations from the Bay of Fundy to far out into the Atlantic and into the Gulf of St Lawrence.