A study released on Wednesday (Feb 28) suggests that the North Pacific humpback whale population has experienced a drastic 20 per cent decline in less than a decade, with marine heatwaves identified as the potential primary cause, signaling a concerning future for these majestic sea creatures.
Following successful conservation efforts and the cessation of commercial whaling in 1976, the humpback whale population in the region steadily increased until 2012.
However, over the past ten years, researchers reported a sharp decline in whale numbers, as published in the Royal Society Open Science journal.
A team of 75 scientists utilized the largest photo-identification dataset ever compiled for a large marine mammal, spanning from 2002 to 2021, to track North Pacific humpback populations.
Using images of the unique tail patterns of the whales, the team recorded over 200,000 sightings of more than 33,000 individuals.
Contrary to expectations that the humpback population would stabilise at its natural carrying capacity, there was instead a significant and steep decline observed from 2012 to 2021.
The number of humpbacks fell by 20 per cent, dropping from approximately 33,000 individuals to just over 26,600.
For a subgroup of whales wintering in Hawaii, the decline was even more pronounced at 34 per cent.
A critical factor identified was the occurrence of the strongest and longest marine heatwave on record from 2014 to 2016, affecting the Pacific northeast with temperature anomalies surpassing three to six degrees Celsius.
This heatwave altered the marine ecosystem and the availability of humpback prey, leading to a more severe decline than anticipated.
Study author Ted Cheeseman, a whale biologist and PhD student at Southern Cross University in New South Wales, expressed surprise at the scale of the decline, estimating that around 7,000 whales likely starved to death during this period.
The scientists hypothesise that the extreme marine heatwave may have reduced the carrying capacity threshold for humpbacks, causing a collapse in their population dynamics.
The inability of humpbacks to adapt their flexible diet is seen as an indicator of broader ocean health issues, affecting not only the whales but also other marine species.
The study emphasises that a warmer ocean produces less food, impacting not only humpback whales but also contributing to declines in the populations of tufted puffins, sea lions, seals, and affecting some commercial fisheries.
While recognizing the success story of the rebound in humpback whale populations due to international restrictions on commercial whaling, the study underscores the new reality of changing oceans that necessitates continued conservation efforts and climate action to ensure the well-being of these remarkable creatures.
(With inputs from agencies)
