Environment: humpback whales once again threatened by ocean warming
There are fewer and fewer humpback whales in the North Pacific.
The population of the largest marine mammals fell by 7,000 individuals between 2012 and 2021, and it's because of global warming and maritime heatwaves, according to a study published February 28 in Royal Society Open Science.
According to Australian researchers, rising temperatures are disrupting the entire marine ecosystem and whales are no longer finding enough food.
In this image taken from a video, a humpback whale splashes into the waters off the US city of Seattle, in the North Pacific, Thursday, November 30, 2023. © Manuel Valdes / AP
By: RFI with AFP
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For centuries,
humpback whales were massively hunted
, almost to the point of extinction: in the 1970s, there were fewer than 1,600 left in the North Pacific.
Then the ban on industrial fishing
allowed the species to recover
.
In 2012, researchers estimated that there were more than 30,000 in the same region, to the point of seeing them removed from the list of threatened species.
But in 2014, an
unprecedented
marine heatwave , which lasted two years, seemed to have halted this recovery.
These temperature anomalies sometimes exceeded three to six degrees Celsius.
Since then, the humpback whale population has declined by 20% in this area,
according to researchers
: from 33,000 individuals to just over 26,600, according to the largest photo-identification dataset ever created. for a large marine mammal studied by a team of 75 scientists.
For a subset of whales that wintered in Hawaii, the drop was even 34%.
“
About 7,000 whales died of starvation
”
This heatwave has reduced and modified the marine ecosystem and the availability of prey for large cetaceans, in particular a type of plankton in the ocean: these tiny organisms are at the base of the food chain and therefore the entire ecosystem sailor who was disturbed.
Result: “
around 7,000 whales mostly died of starvation
,” laments the author of the study, Ted Cheeseman, a whale biologist and doctoral student at the Australian Southern Cross University.
“
It's not just whale food that has declined
,” says Ted Cheeseman, noting a decline in populations of tufted puffins, sea lions and seals.
“
A warmer ocean produces less food
,” particularly due to the decline or migration of phytoplankton, the basis of the entire ocean food chain, he explained.
Upon discovering this, “
I was speechless
,” he says.
“It’s a much stronger signal than we expected
.”
Beyond these mammals, it is the state of health of the entire ocean which is worrying, according to scientists: climate change is the third cause of the collapse of life.
In 2022, another study published in
Frontiers in Marine Science
showed that increasing ocean temperatures also had the effect of chasing humpback whales from their traditional breeding grounds.
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