South Atlantic Humpback Whales Have Rebounded From the Brink of Extinction

A new study estimates that the group’s population has grown from 440 individuals in 1958 to nearly 25,000 today

Humpback whale basking in light at the surface
A humpback whale basks in sunlight at the ocean's surface in Atlantic Ocean off the coast of the Dominican Republic. Photo by Reinhard Dirscherl via Getty Images

Between the late 1700s and mid 1900s, hunters killed at least 300,000 humpback whales around the world. Some populations are still endangered because of their reduced size, but one humpback group in the western South Atlantic has undergone a remarkable recovery. A new study published in Royal Society Open Science estimates that humpbacks in this region now number 24,900—nearly 93 percent of their population size before they were hunted to the brink of extinction.

Western South Atlantic (WSA) humpbacks are one of seven Southern Hemisphere breeding groups recognized by the International Whaling Commission (IWC). They were, according to the study authors, “the first major target of commercial whaling in the Antarctic,” and tens of thousands of WSA humpbacks were killed from the early 1800s onwards. By 1958, there were only around 440 individuals left.

But when the IWC implemented a moratorium on the commercial hunting of all whale species and populations in 1986, the WSA humpbacks had a chance to start recovering. An IWC survey conducted between 2006 and 2015 found that the population had rebounded to only 30 percent of its pre-exploitation numbers by the mid-2000s. But the researchers behind the new report suspected that the survey wasn’t painting a full picture of the humpbacks’ current state.

To calculate a fresh estimate of WSA humpback numbers, the researchers first reassessed how many whales existed before the hunting frenzy began. As Leslie Nemo of Discover reports, the IWC survey did not look at data from before the early 1900s, when hunting techniques became more efficient and whalers started pushing further into sub-Antarctic and Antarctic habitats. Hoping to gain a broader view of the whales’ trajectory, the researchers studied records from before the turn of the 20th century. Hunting methods at the time were “rudimentary,” but WSA humpbacks were nevertheless being pursued. The team also took into account “struck-and-lost” rates—whales that were hit by hunters but ultimately lost at sea—and calves that may have died after their mothers were killed.

In 1830, the study authors estimate, there were around 27,200 WSA humpbacks. In 1904, there were approximately 24,700. By 1926, the population had plummeted to 700.

Once the team had calculated the whales’ historic decline, it was time to take another look at their recovery. The IWC survey had relied on data from aerial counting missions, which likely missed some whales because planes move so quickly, as Alexandre Zerbini, study co-author and marine mammals researcher with the National Oceanic and Atmospheric Administration, tells Nemo. The new study also incorporated data from boat surveys, which move at a slower pace.

Zerbini and his colleagues estimated that nearly 25,000 WSA whales now swim through their habitat. The study authors say there is a “high probability” that the population will have recovered to 99 percent of its pre-exploitation numbers by 2030.

WSA whales are, in other words, a resounding conservation success story. But they aren’t completely out of the woods. Today, the threat of hunting has been replaced by the threat of climate change, which may be impacting the distribution of krill, humpbacks’ primary food source.

“It appears that the krill are moving southwards with global warming, and that could force the whales to compete with penguins and fur seals for food,” Zerbini tells Elizabeth Weise of USA Today.

Still, there is an important lesson to take away from the story of the WSA whales: animals can be incredibly resilient, if only we give them the necessary breathing space.

“This is a clear example that if we do the right thing then the population will recover,” Zerbini tells Weise. “I hope it serves as an example that we can do the same thing for other animal populations.”

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