An Estimated 7,000 North Pacific Humpback Whales Died 2013 - 2021; Starvation From Warming Seas Likely Cause
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After the 1982 International Whaling Commission banned commercial whaling, humpbacks made a remarkable recovery. The new study estimates a peak of nearly 33,500 humpbacks in the North Pacific in 2012, and an average population growth rate of 6% between 2002 and 2013. This 40-year upward trend in the population was so impressive that humpbacks were removed from the US Endangered Species Act in 2016.
That same year, however, an extreme marine heatwave was still warming waters in the north-east Pacific. Maximum sea temperatures recorded from 2014 to 2016 were 3-6C above average. This left fewer nutrients for phytoplankton, the plants at the base of the marine food web. The impacts cascaded across the ecosystem, leaving less food for everything from sardines to seabirds to sea lions.
The new study shows that about 7,000 humpbacks disappeared from the North Pacific between 2013 and 2021, a decline that was likely due to a lack of food. “It was definitely an unusual mortality event,” says Cheeseman. “Humpback whales are flexible, and willing to switch from krill to herring or anchovies to salmon fry. But when the whole ecosystem decreases in productivity, it hurts them big time.”
Sustained heatwaves can cause whales and other marine animals to starve, as was the case with Festus. It can also lead to “skinny whales”, says Cheeseman. “Instead of looking nicely curved, the whales are awkwardly angular.” Skinny whales are more susceptible to disease, and skinny females are less likely to reproduce. Research on humpbacks in Antarctica has shown that warmer ocean conditions mean less food for whales, which results in lower pregnancy rates. Ari Friedlaender, an ecologist in the Ocean Sciences Department at the University of California Santa Cruz who led the Antarctic research and was not affiliated with the North Pacific study, believes that the 2014-16 marine heatwave probably “impacted the pregnancy rates in the population” and also “led to the demise of a certain number of animals” in the North Pacific.
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https://www.theguardian.com/environment/2024/feb/28/did-a-marine-heatwave-cause-7000-humpback-whales-to-starve-to-death-aoe