A seventh calf, but not a baby boom

The North Atlantic right whale population is estimated to number 411 individuals. Of these, about 75 are believed to be females of reproductive age. However, in 2018, no calves were observed and only 5 were spotted in 2017. The number of calves observed each year is therefore quite different from what would normally be expected. Between 2010 and 2016, the birth rate fell by 40%. Additionally, the average interval between births for any given female rose from 4 to 10 years. For comparison, this interval is 3 years for the species’ cousin, the southern right whale. The decrease in the number of completed pregnancies and the increase in the number of undocumented newborn deaths are reasons that might explain these unusual intervals.

Pregnancy and nursing are very energy-intensive processes for females, who require access to sufficient food sources to maintain their body weight. Copepods – a favourite food of right whales – are becoming increasingly rare in traditional summer areas between New England and Nova Scotia. This might explain why a growing number of right whales are being observed in the Gulf of St. Lawrence, where these small crustaceans are present. A longer migration means greater energy expenditures for females, which can be detrimental to reproduction. If, despite the odds weighing against her, the female does manage to give birth to a calf, there is no guarantee that she will be sufficiently fit to produce enough milk to feed her offspring. Indeed, studies on the southern right whale have shown that the body volume of lactating females diminishes by 25% in a span of just 3 months.

In recent decades, there has been a correlation between particularly low birth rates and the observation of more injuries and poorer health overall. This suggests that the low birth rate may be related to the frequent entanglements of North Atlantic right whales in fishing gear. This species is particularly prone to collisions and entanglements, as it is a slow swimmer and stays close to the surface. The stress triggered by these events can affect whales’ reproduction or their ability to terminate their pregnancy. Fortunately, these periods are generally followed by a rise in birth rates when health conditions become favourable again.

Further, the low genetic diversity of right whales might be having an effect on their reproductive capacity. Indeed, small populations are particularly at risk when it comes to mating between individuals that are too closely related genetically. Such individuals may be genetically incompatible and produce non-viable fetuses.

The introduction of right whale protection measures in 2018 by Fisheries and Oceans Canada and Transport Canada appears to have been effective. Authorities have identified 3 entanglements and zero mortalities in Canadian waters in the past year, a dramatic improvement compared to the 18 mortalities and 5 entanglements documented in 2017.

We will need to wait a few years before we can determine whether the decrease in mortality and stressful events will translate into higher birth rates. In the meantime, it is hoped that these three births will be the harbinger of a string of good news for the species.