Humpback whales, long threatened by commercial hunting, once seemed to be doing better. But now it’s the effects of climate change that could threaten their survival in the North Pacific, reveals a study published February 28, 2024 in the journal Royal Society Open Science.
A sharp decline signals a major disruption
Between 2012 and 2021, the number of humpback whales in the area declined by 20%, from 33,000 individuals to just over 26,600, according to the largest photographic dataset ever created of a large marine mammal studied by a team of 75 scientists. For the subgroup of whales that wintered in Hawaii, the decline was even 34%.
With other threats such as ship collisions or noise pollution, the future of the species no longer seems certain, scientists warn, calling for conservation efforts to take climate change more into account.
According to study author Ted Cheeseman, a whale biologist and PhD student at Australia’s Southern Cross University, “about 7,000 whales mostly starved to deathWhile it’s normal for species numbers to fluctuate, even in healthy populations, such a sudden decline in long-lived species portends a major disruption to the oceans.
However, from 2014 to 2016, the Northeast Pacific was ravaged by the strongest and longest marine heat wave ever recorded, with temperature anomalies sometimes exceeding three to six degrees Celsius, altering the marine ecosystem and the availability of prey for large cetaceans.
“This is a much stronger signal than we expected“
“Not only food for whales has decreasedsays Ted Cheeseman, noting the decline in puffin, sea lion and seal populations.A warmer ocean produces less food”, especially due to the decline or migration of phytoplankton, which is the basis of the entire oceanic food chain.
Upon discovering this, “I was speechless“, he declares.This is a much stronger signal than we expectedAnd all the more surprising that humpback whales, once threatened with extinction by commercial fishing in the late 1960s, appeared to be on the road to recovery following a whaling moratorium imposed by the International Whaling Commission in 1982.
In 2016, the United States removed most groups of humpback whales from its endangered species list, following in the footsteps of the International Union for Conservation of Nature (IUCN), which removed them in 2008. “vulnerable” to “the slightest concern”.
But global warming seems to be changing that. Another study was published in 2022 Frontiers in Marine Science showed that increasing ocean temperatures also had the effect of driving humpback whales away from their traditional breeding grounds.