When widespread commercial whaling stopped after the International Whaling Commission’s moratorium came into force in 1986, there was a reasonable expectation that some whale populations would recover. However, a red flag of concern has just been raised for one great whale species – a species that was rebounding after being heavily depleted by whaling. This is the southern right whale (Eubalaena australis), one of the true giants of the sea (growing up to 56 feet/17 metres long) and, up until now, a shining symbol of hope for ocean recovery.
Given our present focus on the climate emergency, it may not come as a surprise that the primary factor threat to their recovery is climate change. However, the current widespread public acknowledgement that climate change threatens all life on Earth is not longstanding. Just a few short decades ago, climate change was more generally viewed as theoretical or, if it was accepted as happening, its consequences were seen as a long way off. For some of us, however, an urgent need to respond was already apparent and, alongside this, a strong conviction that the highly migratory great whales would be especially vulnerable.
Our rationale at that time was based on the whales’ biology and was informed by the fact that conditions at the poles seemed to be changing fast. Many of the bigger whales migrate to feed on the ‘spring blooms’ of plankton that occur in the Arctic and Antarctic. The whales may feed very little elsewhere, so access to these regions and their rich productivity is vital for their survival. After feeding, the whales travel – often hundreds of miles – to warmer and less nutrient-rich waters where they raise their calves. This makes them susceptible to changes in these widely separated feeding and breeding areas and, arguably, also along the migration route between.
In a book chapter about whales and climate change written with my friend Malcolm MacGarvin, and published in 1996, we warned that there were rational grounds for expecting serious adverse impacts on whale populations, concluding that “Unfortunately, as marine top predators – in some cases tied to lengthy migrations and requiring particular resources at particular places – they may be especially vulnerable”.
However, when the International Whaling Commission (IWC) turned its considerable scientific expertise to look at this issue at a workshop in that same year, it ran headfirst into a brick wall. The workshop concluded that it “recognised that given the uncertainties in modelling climate change at a suitable scale and thus modelling effects on biological processes… at present it is not possible to model in a predictive manner the effects of climate change on cetacean populations.” This was a disappointing conclusion but perhaps somewhat reflected the ‘wait and see’ thinking at the time.
Life and science moved on and in a 2009 review I co-authored with Wendy Elliot of WWF, we noted that “a number of studies have recently highlighted [climate change’s] potential impact on cetacean species – for example, there are important linkages between sea ice and krill, the primary prey for baleen whales in Antarctica”. We strongly emphasised the importance of the sea-ice feeding habitat for the baleen whale species and the risk posed by climate change.
In the years that followed, IWC held several more workshops on the effects of climate change on cetaceans. It is about to hold another one later this year. The next workshop meets in an era where predictive powers based on scientific modelling are much improved, and we have a much better idea of how climate change is affecting the seas and the whales. So, with this in mind, let us turn to the new southern right whale research.
There are three right whale species (originally so named because, unhappily for them, they were the ‘right whales’ to hunt): (1) a critically endangered one in the North Atlantic; (2) an endangered one in the North Pacific; and (3) the southern one in the seas south of the Equator, between the latitudes of 20° and 60° south. This latter species was very heavily hunted and its populations crashed. Following protection (which started in the 1970s) a population increase followed. The Right Whale Program (Ocean Alliance and Instituto de Conservación de Ballenas) has monitored individual southern right whales off Península Valdés, Argentina (the main calving ground for the Southwest Atlantic population) since 1971, using photo-ID. The remarkable data series now includes 4,007 known individuals, and this is what the researchers used to examine climate effects.
They found that when the climate anomalies known as El Niño events increased sea surface temperature in the southern right whales’ feeding grounds off South Georgia/Georgia del Sur, the extent of sea ice was reduced and this, in turn, decreased the abundance of Antarctic krill – the primary planktonic prey of the whales. A regional increase of just 1°C over the next 100 years is predicted to cause a 95% reduction in krill abundance by the end of this century.
El Niño events are predicted to increase with climate change and they are linked to decreased whale reproduction and increased mortality. Hence, the researchers conclude that such events are “likely to impede [southern right whale] population recovery and could even cause population decline”.
It is also worth reporting what the distinguished group of scientists who authored this keystone paper said about the ‘ecosystems services’ that the whales provide: “Whales play critical roles in marine ecosystems by vertically and horizontally mixing ocean waters, delivering and recycling nutrients, promoting biodiversity, and mitigating climate change by sequestering carbon for long periods … On their feeding grounds, whales enhance primary productivity by fertilizing ocean waters with feces rich in iron, nitrogen, and phosphorus and distributing other nutrients. Their large biomass and long lives sequester carbon, and when they die, their carcasses contribute to biodiversity and carbon sequestration on the seafloor.”
For most other cetaceans – indeed for most other wildlife – we simply don’t have similar long-term datasets, but it is reasonable to expect that other krill-dependent species will be adversely affected as their food source is reduced.
In conclusion, this new research provides strong evidence for not only a negative impact on a recovering population of whales and highlights the important role that whales play in maintaining healthy ecosystems and helping to lock carbon away. The whales are our unknowing allies in the battle against climate change!
The scientific paper being discussed here ‘Ocean warming threatens southern right whale population recovery’ can be found online here: https://www.science.org/doi/10.1126/sciadv.abh2823
Director of Science