This article comes from the magazine Sciences et Avenir – La Recherche n ° 890 dated April 2021.
“Whales as actors in atmospheric carbon capture”: this is the theme of a discussion to be held on the occasion of the annual meeting of the Scientific Committee of the International Whaling Commission (IWC), from April 27 to April 14 May 2021. This body in charge of whale conservation and hunting management has wanted for several years to highlight the role of these cetaceans in the face of climate change. Because when we talk about carbon reservoirs, we first think of oceans and forests, often forgetting the role of animals, in particular marine ones. Thus, among living beings, it is the whales that constitute the greatest carbon reservoirs. A data which is explained first of all by their gigantism. The pygmy whale, the smallest of the mysticetes, baleen whales, measures six meters on average and weighs more than three tons. On the other end of the scale: the blue whale can reach 30 meters. But these animals are not only huge, they also have exceptional longevity. Thus, the bowhead whale can live 200 years! However, the bigger they are and the longer they live, the more living things store carbon dioxide (CO2), thus protecting the planet from global warming.
Whales allow a redistribution of precious nutrients
Concretely, each whale sequesters an average of 33 tonnes of CO2, the equivalent of the carbon footprint of three French people for a year. Far ahead of what a tree can capture, which stores a maximum of 20 kg of CO2 per year. These astonishing figures were made public in 2019 by a report from the International Monetary Fund. A sign that beyond the ecological aspect, the preservation of whales has a real economic dimension. The storage of CO2 by whales also lasts much longer than their life: several centuries. Indeed, their carcasses join what scientists call dead biomass (or necromass). Their body, made up largely of proteins and lipids, sinks into the ocean, ensuring a major organic enrichment of an environment often poor in nutrients. Ultimately, the carbon that constitutes them can be buried in marine sediments, where it will remain trapped for millions of years. An American team of researchers estimated in 2010 in the journal PlosOne that before their systematic hunting, the whales, by reaching the seabed when they die, made it possible to remove more than 190,000 tonnes of carbon from the atmosphere per year.
But that’s not the only mechanism by which whales capture some of the carbon from the atmosphere. Throughout their life, they dive tens or even hundreds of meters deep to feed on passively floating small plants (phytoplankton) and animals (zooplankton) – or small fish. Then they rise to the surface to breathe. They then release fecal plumes and urinate in their feeding areas, thus diffusing nutrients, as shown in 2014 by the team of Joe Roman, professor at the University of Vermont (United States) (see the infographic). To this vertical displacement, called “whale pump”, is added a second, horizontal this time. The “conveyor belt of the great whales” reflects the migration of many specimens from their resource-rich feeding grounds, for example Alaska, to their poorer breeding grounds, especially off Hawaii or Mexico. Well fed, cetaceans provide nutrients. Thus, the blue whales of the Southern Ocean transport 88 tons of nitrogen each year in their breeding grounds. These two types of movement stimulate the growth of phytoplankton “which captures 37 billion tons of CO2 per year, or a flow – and not a stock – comparable to four Amazonian forests”says Ralph Chami, deputy director of the Institute for Capacity Development, lead author of the 2019 IMF report. In addition, phytoplankton is also a gateway for atmospheric carbon. “It absorbs CO2 from the atmosphere during photosynthesis and transforms it into an organic form which then enters the food web”, remarks Heidi Pearson, researcher in the Department of Natural Sciences at the University of Southeast Alaska (United States).
Fish, carbon pumps also threatened
Like whales, fish sequester a part of the carbon that they take to the seabed when they die. However, if whaling has become scarce, this is not the case for fishing: according to the World Wide Fund for Nature (WWF), today, each human eats on average 19.2 kg of fish per year, about twice as many as fifty years ago. The fish are landed, processed and consumed, thus adding to the CO emissions2 in the air. “The carbon of fish is re-emitted in the form of CO2 in the atmosphere one times these consumed by humans “, explains Gaël Mariani, doctoral student at the University of Montpellier and lead author of a study published in 2020 in Science Advances. According to its results, 94% of the carbon extirpated from the ocean by fishing is re-emitted into the atmosphere by respiration and excretion by humans who have consumed the fish or by the treatment of waste. The last 6% remain trapped in the edges which “are not degraded when they are buried because no organism can”, explains Gaël Mariani. In addition, between 1950 and 2014, fleets targeting large fish emitted around 200 million tonnes of carbon into the atmosphere: 37.5 million tonnes from fish transported on land – the leakage of blue carbon mentioned above – to which is added 165.3 million from ship fuel. For the French researcher, the solution is more sustainable fishing in order to restore fish stocks and thus ultimately increase food biomass and carbon capture.
Credit: BRUNO BOURGEOIS
1000 years of hunting have reduced their biomass by 85%
Humans have hunted them for centuries without knowing the ecological importance of whales. Whether for their meat, oil or baleen: tens of millions of these cetaceans are believed to have been killed during the commercial hunting period that began around the year 1000, when the Basques began to hunt for right whales. of the North Atlantic. Over the next millennium, whale biomass was reduced by 85%! A striking example is that the numbers of blue whales in the Southern Hemisphere have been reduced to 1% of their initial level. The result: populations of large baleen whales now store 9 million tonnes of carbon less than before the advent of whaling, according to the study published in 2010 in the journal PlosOne, led by Andrew Pershing, researcher at Climate Central.
But today, whales face new threats. Because if these cetaceans are in part similar to carbon sinks, the increase in CO levels2 in the atmosphere can also harm them. “The main danger is probably changes in the availability of prey due to variations in water surface temperatures and ocean acidification. , remarks Heidi Pearson. Such a change has the potential to alter the location of foraging areas and migration routes. Which can make it difficult to meet the energy needs of individuals. “ “It is evident that protecting and restoring whale populations will increase their ability to sequester carbon by providing a natural solution to climate change,” says DJ Schubert, wildlife biologist at the American charity Animal Welfare Institute. Protecting whales will not fully mitigate climate change on its own, but it can – and should – be part of the solution. “ It is therefore in this context that the CBI is organizing its meeting. After this, another workshop should focus, this time on the socio-economic issues associated with ecosystem services provided by whales, an idea already mentioned by economists at the International Monetary Fund. Their message: the protection of whales has a cost that should be quantified at the same time as their financial importance.
A minimum “salary” of $ 2 million
Concretely, it is a question of rethinking what the cost of protecting cetaceans means in the light of climate change. “We do not value the value of a whale, but the value of the ‘services’ a whale provides to mankind”, says Ralph Chami. And to continue in a very colorful way: “For example, I work for the International Monetary Fund and I get paid for my work. The whale has worked for humanity by capturing carbon, adding more fish to the ocean and to our plates, and ensuring the tourism but, unlike me, she was not paid for her services. “ He deduces a “minimum wage” of $ 2 million per specimen!
A morally acceptable calculation to reconsider the protection of these animals? “Every creature has an intrinsic value that is priceless , concedes the economist. There is no monetary value possible to value a life. “ The idea is rather to design a compensation while “The current system only values whales when they are dead, cut into pieces and served in certain restaurants.” It is therefore rather a question of valuing their “services rendered” when they are alive, free to move about in a healthy environment. Hence the idea of the IMF to create financial mechanisms to protect them and promote the restoration of their population. This could result, for example, in compensation by a government for a shipping company that would change its route to avoid any risk of collision with cetaceans.
They symbolize the “tragedy of the commons”
The benefits of whales benefit all countries. Yet it is clear that the motivation is lacking to provide them with international protection: a problem called “tragedy of the commons”. The same is true, for example, with the earth’s atmosphere. “It’s the problem of coordination when a resource is shared” says Ralph Chami, deputy director at the Institute for Capacity Development at the International Monetary Fund. As a result, common resources are overexploited and then ultimately destroyed. “