The North Atlantic right whale climbs back above 380 individuals, a third consecutive year of increase

It is rare to be able to write this: the North Atlantic right whale population is increasing. The latest estimate puts it at around 380 individuals, some twenty more than in 2020, and this is the third consecutive year of growth. For a species that was being announced as doomed to disappear, the reversal deserves both explanation and perspective.

A species that had been declining without respite

The North Atlantic right whale takes its name from a time when it was considered the “right” whale to hunt: coastal, slow, and floating once dead. Whaling reduced it to a few dozen individuals by the early twentieth century. Protected since then, it has never recovered its former numbers, and its trajectory had turned downwards again in the 2010s.

Two causes dominate, and both are human: entanglement in fishing gear, in particular the vertical lines of lobster and crab pots, and ship strikes.

How 380 whales are counted

A population of this order allows a method impossible elsewhere: the individual census. Every right whale carries callosities on its head, thickened patches of skin colonised by small white crustaceans, whose arrangement is specific to the individual and stable over time.

A photographic catalogue maintained since the 1980s lists the animals one by one in this way, with their genealogy, their scars and their injury history. The abundance estimate is therefore not a statistical extrapolation from a sample, but a head count corrected for the probability that a living animal was not photographed in a given year.

Two consequences follow. First, the estimate is published with a lag of several years: declaring an animal dead requires several seasons without seeing it again. Second, it comes with a credible interval, and a gap of some twenty individuals between two years is read inside that interval. Our pages on tracking technologies compare this approach with tags.

A mortality event still open

The qualification that prevents any claim of victory lies in an American administrative mechanism: the Unusual Mortality Event, declared for this species in 2017 and still running.

Animals involved since 2017	176
of which dead	43
of which seriously injured	41
of which injured or sick without immediate severity	92

Set against a population of 380 animals, these 176 individuals amount to close to half the population affected, to varying degrees, in less than ten years. A serious injury in a female of breeding age weighs for a long time, in a species whose interval between two births is counted in years.

Females, the bottleneck of the species

An overall population figure says little here. What determines the future of this population rests on a much narrower subset: females of breeding age, whose number is counted in tens.

Three quantities matter for them. The age at first calving, which has lengthened over the decades. The interval between two births, historically about three years, which then rose to six or more in difficult periods. And the survival of the calf during its first year.

These three indicators deteriorate when females are in poor body condition, which chronic entanglement brings about just as much as a year of scarce food. A population can therefore decline without any animal dying visibly: it is enough for births to become further apart. Our pages on demographics and life cycles set out these parameters.

This is also what explains the caution of researchers faced with the current increase. Recent calving seasons have been better than the catastrophic ones of the late 2010s, but a good run of births may reflect temporary favourable feeding conditions as much as an underlying recovery. Telling the two apart will take several more years.

Why the increase remains fragile

Three years of growth do not make an established trend, especially at this scale. Some twenty more animals is the order of magnitude of a good calving season, which a few ship strikes can wipe out.

The conservation status does not change, for that matter: the species remains listed as Critically Endangered, a category set out on our page on IUCN conservation statuses. What changes is the direction of the curve.

Why an entanglement kills slowly

Two mechanisms need to be distinguished here, because they are not addressed in the same way.

A ship strike involving a large vessel often kills outright, or in the days that follow. The event is a single point in time and, when the carcass is found, the necropsy documents it.

An entanglement works differently. A whale carrying several tens of metres of rope swims with added drag for months, sometimes years. The extra energy cost is permanent, and it is paid first out of reproduction: a female in poor condition does not conceive, or does not carry her gestation to term. The rope can also cut progressively into the tissues and cause infection.

This is why the “seriously injured” line of the tally counts almost as much as the line for deaths. These 41 animals do not appear among the dead, but their demographic contribution is largely compromised. Our page on bycatch sets out these delayed effects.

The northward shift, the forgotten cause of the crisis

The mortality event opened in 2017 has an origin that is rarely summarised: the whales changed address.

These animals feed on small copepods that they filter at the surface. From the middle of the 2010s, the warming of the Gulf of Maine altered the distribution of this resource, and the whales moved in large numbers into the Gulf of St Lawrence, an area where they had previously been scarce.

There they found dense shipping traffic and pot fisheries, without any of the protective measures built up further south over thirty years. Mortality followed immediately. Canada then introduced speed reductions and dynamic closures, adjusted according to detections of animals.

The episode illustrates a mechanism that will be found elsewhere: protection pinned to a map becomes inoperative as soon as the animals move, and the climate moves them. Our pages on climate change and the international legal framework address this mismatch between fixed zoning and mobile distribution.

What this says about the measures taken

The recovery coincides with a set of provisions applied in recent years: mandatory speed reduction zones for vessels, seasonal fishery closures, development of gear without vertical lines. Establishing a cause and effect link would require a dedicated analysis, and nobody has published that demonstration.

But the coincidence is consistent with what is observed elsewhere, in particular in the Bay of Biscay, where a seasonal closure reduced dolphin bycatch by 60%. In both cases the lever is the same: reduce the encounter between the animal and the gear. Our pages on cetacean demographics and the international legal framework put these mechanisms in context.

Sources: NOAA Fisheries, abundance estimates and monitoring of the unusual mortality event for North Atlantic right whales; partner stranding networks on the east coast of the United States.