The urban whale: What makes right whales unique

Right whales have been featured in the news a lot lately because of an unprecedented number of deaths in the Gulf of St. Lawrence.

Kim Davies, a post-doctoral fellow in Dalhousie University's department of oceanography, said that the dwindling population has been a source of worry for years.

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"This year is just, I don't know, it comes on after we've been concerned about right whales since about 2010," she said.

"So just to have this happen now, after concern for so long is really disheartening."

Davies said that right whales are unique among baleen whales in several ways, some of which could be contributing to the deaths. 

Eating by design

Diet is one key difference according to Davies.

Right whales eat one specific type of zooplankton called calanus, a marine copepod, and they only eat it at a particular time in the organisms life-cycle.

The calanus feed through the winter and early spring, then go into hibernation and by mid-summer are accumulating in basins throughout the North Atlantic.

Right whales' diets consist solely of the calanus, whereas other baleen whales eat it as well as small fish and other types of zooplankton.

Davies said that right whales are "morphologically and physiologically" designed to feed on the calanus. 

"Unlike most other things in the ocean, they're actually able to digest this fat that's inside of this particular life stage of their food," Davies said.

'Like a lawnmower'

Right whales also forage for food differently than other baleen whales through ram-filter-feeding.

Davies said they have two rows of baleen, what she described as a bristle-like filter in their mouths, the front row with a gap, and the back row with two gaps.

"They can just skim through the water and … water will come in through the gap in the front and go out through the gaps in the back," she said. 

This offers them a unique way of feeding without having to slow down.

"They can continuously swim and just filter, filter, filter that water without ever having to do any gulping or anything like that." 

"So that allows them to dive down to 200 metres and essentially open their mouths and swim without losing any power."

"It's a totally different way of feeding … like a lawnmower."

Where they eat

Davies said their uniquely particular eating habits bring them to the specific areas where the calanus congregate.

The basins where calanus collect become feeding points for the right whale community.

Because they are looking for these very specific zooplankton at a particular time in their life-cycle, the right whales are looking for areas of ocean which are supportive of a calanus population. 

"Those conditions do not occur everywhere there's very particular oceanographic conditions that aggregate their food," she said.

"To expend all that energy and dive down to 200 metres and you know filter out all that food and stuff, it takes a tremendous amount of energy so they are looking for really highly concentrated patches of their food."

Coastal whales

The way right whales feed, what they eat, and where they have to go to find calanus may be a contributing factor in the deaths in the Gulf of St. Lawrence.

Davies said that calanus collect in shallower waters, which bring the whales within 100 kilometres of the coast. 

These are busier areas of the water which are also more dangerous for them.

"They're the same areas where there's all different kinds of industrial activities," she said.

"All different kinds of fisheries go on in these areas, there are shipping lanes, habitual traffic patterns, there's large vessels, there's smaller vessels." 

For this reason, she said, right whales have been referred to as "the urban whale."

'No silver bullet'

Davies said that there are a number of contributing factors into the high number of right whale deaths.

"There's no silver bullet that is going to answer the question of why all these right whales are dying this year," she said.

"The last several years have been bad for right whales."

Davies said that fewer calves are being born each year, which could indicate a stress of some kind on the population.

She also said that there has been a substantial decline in sightings in their usual habitats, which suggests that the food supply in those areas is insufficient.

"These are all potentially mitigating factors that are contributing to reduced health in the population," she said. 

This reduced health could be another factor in the die-off.

"A combination of the health of the population, the fact that they're migrating widely in search of food, and I don't know potentially other factors that we haven't thought of yet," said Davies.

She said that right whales have encountered fishing gear and ships for years but their reduced health could make them "more susceptible to mortality if they do encounter a threat."

"So why all the deaths this year? I can't help but think that the health of the population may have something to do with it."

"It's unprecedented, it's unique and I don't why they're all dying."

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