Why do whales and other cetaceans wash up on our beaches?

Unfortunately, the stranding of whales and other cetaceans is a relatively common occurrence. In a context where societies are very sensitive to the preservation of animal life and the conservation of species, many people are sorry about this situation and aspire to be able to stop it. But for that, it would be necessary to understand what are its causes. However, we are still far from being able to explain with precision what caused these massive strandings. Scientists are working on some hypotheses that we present to you here.

Strandings in mainland France

In 2019, 2,282 strandings of marine mammals were recorded. This concerns 83% of cetaceans and 17% of pinnipeds. These figures exceed the average calculated over the last 10 years. This clear increase is due to the increase in strandings of common dolphins in the Atlantic, particularly in winter. These events are clearly linked to the catches in fishing gear. This same cause has also been identified for harbor porpoise strandings.

If the links with fishing activity seem clear for the situation in mainland France, the causes of cetacean stranding in other places on the planet still pose many questions. Here are the main assumptions scientists are working on.

Exhaustion and illness

Many cetaceans are required to make long journeys that can reach 10,000 km in distance, as part of migrations. Whales travel at a speed of between 5 and 20 km / h, thus traveling between 75 and 200 km / day.

The motivation for these movements is to reach waters richer in food or gathering points where males and females can meet to reproduce. It can also involve reaching places where predators are less numerous to better protect the young. The trajectories and times of migration vary according to the species: for example, the humpback whales have North / South migrations, the harbor porpoises leave the coastal areas in winter to move away offshore far from the ice.

Migration subjects animals to contexts which can prove to be trying. Cetaceans can thus encounter storms days that push them to the end of their strength. Animals can also be sick. It has thus been shown that the strandings of blue and white dolphins in the Mediterranean during the 1990s and 2000s were mainly caused by the Dolphin Morbillivirus (DMV). By causing pneumonia, encephalitis and damage to the immune system, this virus makes cetaceans unable to swim. In Australia, disease is the most common cause: a stranded animal is usually sick.

Solar storms

We are still far from understanding how the metabolism of cetaceans works, and in particular what allows them to locate themselves during their migratory journeys. Some scientists hypothesize that cetaceans locate themselves by relying on the Earth’s magnetic field, due to the presence of magnetite in their meninges which would make them sensitive to it. However, the perception of the Earth’s magnetic field can be disturbed by solar storms. Disoriented in this way, the animals would lose their routes and run aground on our coasts.

Sound pollution

In May-June 2008, a hundred of Electra’s dolphins stranded on the coast of Madagascar. Questions about the cause of the incident led the researchers to study, in addition to the causes mentioned above, the hypothesis of the noises emitted by the sonars. Indeed, the incident coincided with the displacement of an oil research boat.

Certain noises propagated underwater, such as explosions during marine surveys or sounds propagated by sonar, could interact with the echolocation system of cetaceans, or even reduce their hearing capacities. The bioacoustics laboratory of the Polytechnic University of Catalonia has thus shown the link between certain human sources of marine noise and the number of collisions between these marine mammals and boats. However, noise is currently used by fishermen to keep cetaceans away from activity areas and prevent them from being caught in fishing nets. The benefits of using noise to save cetaceans could therefore be questioned.

Save the cetaceans that wash up

Australia and New Zealand are known for the frequency and importance of cetacean strandings. Also, these countries have developed real know-how in the rescue of these animals. In 2017, when more than 600 pilot whales were stranded in New Zealand, rescuers managed to save around 400. But in September 2020, when more than 460 of these same animals found themselves stranded in a bay remote Tasmania, the implementation of a large rescue operation only saved about fifty cetaceans.

In France, Raymond Duguy created in 1970 the National Stranding Network (RNE) to intervene on the metropolitan coast and overseas. It is a network that includes more than a hundred organizations that intervene on more than a thousand strandings identified annually. It is scientifically coordinated by the Pelagis Observatory located in La Rochelle, and placed under the supervision of the Ministry of Ecology. Interventions are based on local correspondents ready to intervene, who can be associations, communities or individual volunteers. This organization contributes to research to understand these phenomena by collecting data for each stranding on which it can intervene.

Let’s stay optimistic

Some species of whales see their populations increasing. Of course, despite a ban on international trade in whale products, each year nearly 1,000 whales are deliberately killed for trade. However, the International Union for the Conservation of Nature (IUCN) has revealed what may come as a surprise in a context where nature seems to be in bad shape: the world’s population of fin whales has almost doubled since the 1970s, now numbering nearly 100,000 individuals. The gray whale (Eschrichtius robustus) changed from critically endangered to endangered only. The population of humpback whales (Megaptera novaeangliae) is also developing positively. In 1830, the numbers were estimated at some 27,000 individuals. By the mid-1950s, they had dropped to 450 individuals. But today, these whales are once again close to 25,000. Commercial whaling bans, international agreements and other protective measures are therefore bearing fruit. Humans seem to be able to reverse trends and act in favor of species protection.

Global warming

Gray whales (Eschrichtius robustus) benefit from protection actions implemented in Mexico since the 1970s. They come to reproduce and give birth to their young in Baja California, in the coastal lagoons. While the species had come close to extinction, there are now more than 25,000 individuals. But since the beginning of 2019, in one year, more than 400 gray whales have died stranded on the coasts of the Pacific, from Canada to Mexico. The evolution of populations therefore remains under surveillance. Global warming is a cause considered to explain their recent strandings. By causing the water temperature to increase, it would cause the scarcity of feeding grounds for these animals in the North Pacific. This ultimately joins the hypothesis of the exhaustion of animals who would not find enough food to face the ordeal of migration.

However, whales are proving to be real players in the fight against climate change. Indeed, these play a real role in the capture of carbon dioxide (CO2) of the atmosphere. It is estimated that a whale stores around 33 tonnes of CO2. And if she dies naturally, this CO2 walks in the depths of the sea where it remains trapped. The consequences are obviously very different if the whale dies stranded.