Uncertain future of the North Atlantic right whale linked to its tiny prey

The fate of one of the world's largest living animals depends on one of the smallest.  

Scientists are studying a northward shift of the North Atlantic right whales and their speck-sized prey that could push one of the rarest whales on the planet closer to extinction.

Their main food, Calanus finmarchicus, commonly called copepods, a type of tiny zooplankton, is showing up in higher concentrations in the Gulf of St. Lawrence than in areas traditionally frequented by the endangered whales, such as the Gulf of Maine and Bay of Fundy.

The shift has put the whales in waters rife with shipping and fishing-gear hazards — with deadly consequences for the already endangered population.

DEEP TROUBLE | Right whale in peril

After an unprecedented number of deaths this summer, CBC News is bringing you an in-depth look at the endangered North Atlantic right whale. This week, in a series called Deep Trouble, CBC explores the perils facing the right whales.

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Eleven whales, of the estimated 500 remaining, have been confirmed dead in the Gulf of St. Lawrence this summer.

"It's getting really warm in the Gulf of Maine, and it's warming faster there than anywhere else around," said Stéphane Plourde, a Fisheries and Oceans researcher.

"The Calanus don't prefer those conditions."

The 60-tonne North Atlantic right whale feeds on prey that are normally less than a millimetre long. The tiny crustaceans float in the water by the billions.

Right whales swim through large pockets of the copepods, gulping up millions per mouthful, before sifting out excess seawater.

Although copepods are found throughout the North Atlantic Ocean, whales need dense plumes of them in order to gain energy from each deep feeding dive.

This summer it appears this need led the whales to the Gulf of St. Lawrence, where the copepods were plentiful.

"The region is shallow, which means that this food is concentrated near bottoms instead of being more, let's say, diluted in the water," said Plourde.

One of Plourde's models shows a heat map overlaid on a graphic of Atlantic Canada.

The Gulf of St. Lawrence beams bright red, signalling high densities of copepods. The colours shift to orange and then blue farther to the south, signalling that the crustacean population is dwindling.

"We don't know what the impact will be for the right whale habitat quality with these fluctuations," Plourde said.

"It certainly suggests that the zooplankton community will change. It's already changing."

Protection measures

Right whales were not seen in their typical abundance this summer in the Bay of Fundy off New Brunswick or in Roseway Basin off the southern tip of Nova Scotia.

Those waters have protection measures in place for the whales, with adjusted shipping lanes and "area to be avoided" status, reducing the chances of ships striking the animals.

Plourde's research is used by Fisheries and Oceans to support species-at-risk management and fisheries management.

In August, the federal department ordered a temporary slowdown for large vessels in the Gulf of St. Lawrence.

If Fisheries and Oceans can use the mapping to understand where the whales will likely be next year, it may be able to implement additional or permanent protection measures for the whales.

Less food, fewer offspring

Plourde's research and that of others in the field has found that the overall abundance of copepods is decreasing — yet another hurdle in recovery for the dwindling species.

"Right now, the Gulf of Maine is kind of that southern edge of their territory," said Erin Meyer-Gutbrod, a post-doctoral scholar in marine phenology at the University of California, Santa Barbara.

"They prefer cold water. So as the waters warm, and the copepods want to stay in the same colder waters that they are accustomed to, all these models have predicted that the copepods will actually just shift north and essentially abandon the Gulf of Maine."

For years Meyer-Gutbrod has studied how copepods respond to changing temperatures and how they affect the right whale population.

"We've found that when there's a period of years and prey is low and less available for the right whales, they reproduce slower," said Meyer-Gutbrod.

"Ideally, they would be giving birth every three years. They are pregnant for a year, they lactate for a year, and they rest and rebuild blubber for a year, and then they can get pregnant again."

Fisheries and Oceans Minister Dominic LeBlanc has said that government will bring "absolutely every protection to bear" to prevent any more deaths than the 14 that have been confirmed since early June off Canadian and U.S. coasts.

But while big changes may be coming, it's the small ones in ocean temperature that could eventually prove the greater threat.