Climate change could slow recovery of southern right whales

Nicolas Lewin, mother and calf south right whales Nicolas Lewin
Climate change could lead to more severe El Nio weather events, which may hinder the recovery of the southern right whale population off the coast of Argentina.

The number of southern right whales have increased since whaling was banned in the 1930s. However, it is not clear how climate change will affect their recovery.

El Nio is a weather phenomenon caused by warm ocean water moving from Australia and Indonesia to South America.


According to Macarena Agrelo, a Brazilian professor at the Federal University of Santa Catarina (Brazil), climate change is likely to increase El Nio events and make them more frequent.

This causes the West Antarctica ice shelves to melt, which can lead to a decrease in the abundance of the krill, which is a major food source of southern right whales.

Agrelo and her collaborators analysed data from Southern Right Whale Program. This program has followed 1380 female whales in a larger population around the Valdes peninsula off Argentina's south-east coast since the 1970s. It was used to predict how El Nio events would affect whale survival.

Agrelo says that I was modeling the numbers of female whales over time and noticed that they fluctuated in number over the years. After looking at the patterns, it became apparent that they were El Nio year.

Researchers speculate that a decrease in krill abundance in El Nio years may lead to the death or rebirth of pregnant female whales.

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Female whales become thin after giving birth and during lactation. They need to rest for a year. Agrelo says that if the availability of krill is reduced, females could die due to lack of food.

The team forecasted whale population growth in different climate scenarios.

The population is likely to reach 85 percent of its pre-whaling size of 35,000 whales if El Nio events are as frequent and intense as they were in the past 50 years.

The worst case scenario, a 4.4C increase in global average temperature above preindustrial levels by the century's end, gives the population no chance to reach 85 percent of pre-exploitation.

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The best scenario for a more optimistic scenario, in which global temperatures rise is unlikely exceed 2C, could see the whales reach 90 percent of their pre-whaling size.

Anthony Richardson, from the University of Queensland in Australia, said that the study provided compelling evidence that climate change could have an impact on the recovery of the southern right whales.

These findings emphasize the importance of climate action. Whales play a key role in marine ecosystems. They lock carbon in their bodies for many decades, until their carcasses fall and then support biodiversity on the ocean floor. Agrelo says that whale faeces are also able to fertilize the ocean with nutrients like iron which, in turn, supports krill populations.

Journal reference: Science Advances, DOI: 10.1126/sciadv.abh2823

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