Once nearly extinct, humpback whale populations are bouncing back, a sign that protections for the massive mammals have been at least somewhat successful.
Researchers tracked the rebound of western South Atlantic humpback whales in a study published Wednesday in the journal Royal Society Open Science. They found that this portion of the world’s humpbacks has recovered to around 93 percent of the size its population was before centuries of human activity left the whales nearly extinct.
The new study builds on previous work looking at humpback populations in this part of the Atlantic Ocean. It takes into account deaths that may be less conspicuous: those struck by whalers but lost at sea, and calves who died because their mothers were killed.
The whales’ strong recovery, the researchers say, is thanks to efforts to conserve and protect the oceans from humans.
Before the success story of the western South Atlantic humpback came a close call with extinction. Centuries of exploitation by humans decimated populations; by the mid-1950s, only 450 of the species remained in the ocean. That’s down from 27,000 whales in 1830.
“This population was hunted since at least the early 1800s,” the researchers write, “but it was most heavily impacted by commercial whaling during the early 1900s once whaling expanded to high latitudes.”
This group of humpback whales migrates toward feeding grounds in higher latitudes near South Georgia and the South Sandwich Islands during the spring, remaining there until autumn.
Historically, whalers took advantage of those patterns to cash in.
Now, having the humpbacks back in action could cause rippling effects in their ecosystems, the researchers say. The whales’ main food source, Antarctic krill, could see a big drop in population now that the whales have rebounded.
More humpback whales also mean more competition for krill around the South Georgia and South Sandwich Islands, which could affect other krill-eating species like Antarctic fur seals and penguins.
And warming ocean waters continue to pose threats to ocean life.
“Continued monitoring is needed to understand how these whales will respond to modern threats and to climate-driven changes to their habitats,” the researchers write.
Abstract: The recovery of whale populations from centuries of exploitation will have important management and ecological implications due to greater exposure to anthropogenic activities and increasing prey consumption. Here, a Bayesian population model integrates catch data, estimates of abundance, and information on genetics and biology to assess the recovery of western South Atlantic (WSA) humpback whales (Megaptera novaeangliae). Modelling scenarios evaluated the sensitivity of model outputs resulting from the use of different data, different model assumptions and uncertainty in catch allocation and in accounting for whales killed but not landed. A long period of exploitation drove WSA humpback whales to the brink of extinction. They declined from nearly 27 000 (95% PI = 22 800–33 000) individuals in 1830 to only 450 (95% PI = 200–1400) whales in the mid-1950s. Protection led to a strong recovery and the current population is estimated to be at 93% (95% PI = 73–100%) of its pre-exploitation size. The recovery of WSA humpback whales may result in large removals of their primary prey, the Antarctic krill (Euphausia superba), and has the potential to modify the community structure in their feeding grounds. Continued monitoring is needed to understand how these whales will respond to modern threats and to climate-driven changes to their habitats.