Southwest Atlantic Humpback Whales are Making a Comeback From Extinction

After numbers that nearly placed them near extinction due to commercial hunting, Southwest Atlantic humpback whales have made a comeback that have placed them at numbers similar to the early 20th century. They are now listed as being under the "least concern" among whales on the IUCN List of Endangered Species.

It's estimated that before the early 20th century, 27,000 whales once swam the seas. Their numbers had been reduced to just a few hundred over time by whalers. But a new study shows that their numbers have increased to 25,000, 90 percent of where they were before harpoons and hooks decimated their populace.

There are seven Southern Hemisphere pods of Southwest Atlantic humpback whales, each of which are unique in their genetic makeup and behavior. The group used in the study have their winter breeding grounds off the coast of Brazil, and in the summer travel to the Antarctic, where they feast on krill.

In 1904, commercial hunting of whales in the region began, and with it the decline of their numbers. By 1920, the whales were barely visible.

"It's a positive story," said Dr Alex Zerbini to the BBC. Zerbini is the report's lead author from the National Marine Fisheries Service, part of the US National Oceanic and Atmospheric Administration (NOAA).

"South Georgia's whaling stations were able to continue by switching to other species, going after blues, fins, and then sei whales. It was a sequential collapse," Dr Zerbini told BBC News.

"Finally, they went after minke whales, the smallest of the great whales, before the moratorium was introduced in the 1980s."

A whale surfaces near a small New York town. Artie Raslich/Getty

The humpback whale entered protection during the 1960s, and aside from some illegal Russian whalers the populace has been allowed to thrive.

"But we didn't really measure anything until the 1980s and it wasn't until we did the first proper assessment at the start of the 2000s that we realised just how well they were recovering," Dr Zerbini said.

As the oceans warm, there has been concern about the survival of the whales' food supply. There's evidence the krill are restricting their range, retreating poleward as the oceans warm.

"There has been a southward shift in krill in the south Atlantic and what that might mean for whales is that they may have to travel further south to find optimum feeding grounds," co-author Dr Jennifer Jackson from the British Antarctic Survey told BBC News. "And, potentially of course, a reduction in krill is going to affect the number of whales that can be supported by the habitat."