The right whale, which can weigh up to 60 tonnes, feeds only on copepods, more specifically calanus, barely as big as a grain of rice. (Archive photo)
Joane Bérubé (View profile)Joane Bérubé
Knowing where the North Atlantic right whale's food accumulates could help to better predict its movements. At least this is the hypothesis underlying the modeling work of biologist and zooplankton specialist at the Maurice-Lamontagne Institute, Stéphane Plourde.
The North Atlantic right whale is a foodie that eats only one type of zooplankton. It is precisely because it is looking for tiny, very specific crustaceans that the whale is increasingly frequenting the Gulf of St. Lawrence.
Modeling feeding sites is therefore a matter of interest since it would help to better protect the whale from collisions or entanglements. The answer, however, requires knowing what this large cetacean actually eats.
Modeling makes it possible to fill in the holes both spatially and in the season, in the year, then if we are able to have confidence in these inferences, this could inform us about places that we known less, but which could become feeding sites, explains Stéphane Plourde.
Data from the last 20 years were used to generate a three-dimensional prediction. This means, specifies Mr. Plourde, that we predict the quantity and depth of these prey, on a seasonal scale, that is to say monthly.
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The work is being done in collaboration with the Americans and the result will be cross-border. The probable feeding sites will in fact be established from Cape Hatteras, North Carolina, to the Labrador plateaus.
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A zooplankton specialist, Stéphane Plourde works with researchers from Canada and the United States.
Modeling feeding sites could also help to identify potential future right whale habitats by integrating other elements, such as water temperature, into the model.
This large whale, which can weigh up to 60 tonnes, feeds only on copepods, more specifically calanus, which measure between 3 and 5 mm, barely as big as a grain of rice.
Historically, the right whale fed primarily on a single species of copepod, named Calanus finmarchicus, a subarctic species from the northern Atlantic , reports the biologist.
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The right whale is not a very fast whale. (File photo)
These are the currents that transport these calanus from the Labrador Plateau to the southern Gulf. These places are replenished with calanus each spring. But in recent years, the whale has been wandering and becoming more and more present in the waters of the Gulf, further north.
That's because its favorite delicacy does not like warm water and is becoming less and less abundant on the Scotian Shelf, particularly in sites designated as critical whale habitat, such as the Bay of Fundy.
Its prey is also not very abundant in the St. Lawrence, its presence probably being limited by the too cold temperatures of the Gulf of St. Lawrence and the coasts of Newfoundland.
It is not excluded, underlines Stéphane Plourde, that in the future, warming waters will promote greater productivity of Calanus finnmarchicus further north.< /p>
However, it is not necessarily this species that the right whale in the St. Lawrence is currently looking for. The animal appears to have slightly modified its diet.
Two species of calanus of Arctic origin, available in the St. Lawrence, are likely to appeal to the right whale. They have different sizes, but are also sometimes in certain places or at certain times very, very abundant and important in terms of quantity, observes the Fisheries and Oceans Canada researcher.
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This is what the Calanus hyperboreus type copepod looks like in the laboratory. It is one of the zooplankton species at the heart of the work carried out by researchers at the Maurice-Lamontagne Institute, in the estuary and Gulf of Saint Lawrence.
It's difficult to say that it mainly eats one species, notes Stéphane Plourde, but it's clear that their feeding pattern means the places they occupy, the depths where they dive, this often corresponds to the sites where these calanus species are most abundant.
In the south of the Gulf, Calanus hyperboreus< /em> seems to have somewhat replaced Calanus finmarchicus in the usual historical habitats because there are much fewer of them, adds the scientist.
Calanus hyperboreusdominates in May, June and July and seems to be the reason why the whales come to the south of the Gulf, in the Shediac Valley. It is replaced by another species towards the end of summer.
According to researchers, the right whale really targets the period when zooplankton, caninus, will have the most lipid reserves.
Stéphane Plourde emphasizes that scientists do not know, however, whether the quantities of calanus available are sufficient to meet its energy needs or to ensure its reproduction.
DFO researchers have developed a bioenergetic model of right whale diet that provides an idea of the zooplankton densities needed to meet the whales' needs. With the data we sample, we very rarely measure it. So that means that these aggregations dense enough to support the right whale are probably quite rare. It happens in particular places.
On the other hand, the maximum density of zooplankton in the water column remains difficult to assess due to the tools used until now. It would possibly be underestimated, according to Stéphane Plourde.
Currently, the Shediac Valley, very frequented by whales from late spring to fall, is a targeted site due to fishing activities and maritime transport. The movements of the whales are under close surveillance to avoid entanglements and collisions.
Observation efforts are in some places much less important.
South of Anticosti or north or even east of Havre-Saint-Pierre, the part that is the Lower North Shore, we rarely go there, but that doesn't mean that the right whale doesn't go there.
A quote from Stéphane Plourde, researcher at the Maurice-Lamontagne Institute
The result work will be presented in February 2024 during a week of scientific meetings dedicated to the North Atlantic right whale.
