The number of North Pacific humpback whales plummeted 20 percent in less than a decade, and marine heatwaves may be the main culprit, according to a study released Wednesday that spells a troubled future for the majestic sea mammals.
Thanks to conservation efforts and the end of commercial whaling in 1976, the region’s humpback population steadily increased until 2012.
But over the last decade, whale numbers have declined sharply, researchers reported in the journal Royal Society Open Science.
A team of 75 scientists compiled the largest photo-identification dataset ever created for a large marine mammal to track North Pacific humpback populations from 2002 to 2021.
Using images of the whale’s unique tails the team was able to log some 200,000 sightings of more than 33,000 individuals.
Up to 2012 the humpback population steadily increased, and it was widely assumed it would eventually level off at their natural “carrying capacity” – the number of whales the ocean can support.
Instead, they saw a steep population decline.
From 2012 to 2021 the number of humpbacks fell 20 percent from some 33,000 individuals to just over 26,600.
For a subset of whales that wintered in Hawaii, the drop was even more pronounced: 34 percent.
That turned out to be a highly significant difference.
From 2014 through 2016 the strongest and longest marine heatwave ever recorded ravaged the Pacific northeast with temperate anomalies sometimes exceeding three to six degrees Celsius, altering the marine ecosystem and the availability of humpback prey.
