Discovered 7,000 humpback whales starved to death because of the heat wave

The number of humpback whales in the North Pacific has plummeted 20% in less than a decade. According to researchers, the cause may come from a heat wave at sea.

In 1972, a humpback whale nicknamed Festus was first discovered off the coast of southeast Alaska (USA).

The number of humpback whales in the North Pacific has decreased by 20% in less than a decade. (Photo: Deep Blue Charters).

For the next 44 years, it returned here every summer to feed in the cold, nutrient-rich waters of the North Pacific before heading to Hawaii to breed in the winter.

However, in June 2016, Festus' body was discovered in Glacier Bay National Park. The main cause is starvation - which scientists believe was likely caused by the most extreme heat wave ever recorded in the sea, according to the Guardian.

New research, published on February 28 by Royal Society Open Science, shows that humpback whale populations in the North Pacific decreased by 20% between 2013 and 2021, after warm waters rather than disrupting the ecosystem.

'The marine heatwave (2014-2016) actually reduced ocean reproduction, severely impacting humpback whale populations ,' said Ted Cheeseman - a biologist at Southern Cross University in Lismore ( Australia), who is also the head of the study, said.

Humpback whale Festus, died near Glacier Bay in June 2016. (Photo: Craig Murdoch/NOAA Marine Mammal Health and Stranding).

Unusual death event

Humpback whales can weigh up to 40 tons and are up to 17 meters long, famous for their ability to "compose" melodious songs in the deep sea and their fascinating performances when jumping out of the water. But this animal almost became extinct due to centuries of hunting.

By 1976, the number of humpback whales in the North Pacific may have dropped to 1,200-1,600 individuals.

After the International Whaling Commission banned commercial whaling in 1982, humpback whale numbers recovered significantly.

The new study estimates a peak of nearly 33,500 individuals in the North Pacific in 2012. The average growth rate was 6% from 2002 to 2013.

This upward trend has lasted for 40 years and is so impressive that the humpback whale was removed from the US Endangered Species Act list in 2016.

That same year, however, an extreme marine heat wave continued to warm waters in the northeastern Pacific. The highest sea water temperature recorded from 2014 to 2016 was 3-6 degrees Celsius higher than average.

This reduces the amount of nutrients for phytoplankton, plants at the bottom of the marine food chain. As a result, the impact spreads throughout the ecosystem, leading to less food for everything from sardines to seabirds to sea lions.

Prolonged heat waves can starve whales and other marine animals. (Photo: Marine Mammal Research Program/Pacific Whale Foundation).

New research shows that about 7,000 humpback whales disappeared from the North Pacific between 2013 and 2021. This decline may be due to lack of food.

'It was definitely an unusual death event ,' Cheeseman said. 'Humpback whales have a very flexible diet, being able to switch from consuming krill, to herring or anchovies. But when the entire ecosystem declines in numbers, it's damaging. big for them'.

Effects of heat waves

Prolonged heat waves can cause whales and other marine animals to starve to death , as was the case with Festus.

Cheeseman said this phenomenon could also lead to 'skinny whales'. These whales are more susceptible to disease and have poorer reproductive ability.

Research on humpback whales in Antarctica also shows that warmer oceans mean there is less food for the whales, leading to lower pregnancy rates.

Ari Friedlaender - an ecologist at the University of California Santa Cruz who leads Antarctic research - believes that the 2014-2016 marine heat wave could 'impact pregnancy rates in the population'. It even 'led to the extinction of certain animal species' in the North Pacific.

To estimate humpback whale numbers over the past two decades in the North Pacific, Cheeseman and his colleagues used the largest image identification database compiled for whale populations.

Named Happywhale - this database is made up of hundreds of thousands of images of humpback whale tails contributed by 46 research organizations and more than 4,000 scientists from many countries.

Heat waves may be responsible for the decline in whale numbers in the Pacific Ocean. (Photo: Bekah Lane/the Marine Mammal Center).

Martin van Aswegen, a graduate student at the University of Hawaii at Manoa, used drones to study humpback whales born in Hawaii.

Over the past six years, Van Aswegen has calculated the length, width and body mass of more than 7,500 whales, tracking them from their breeding grounds in Hawaii to their feeding grounds in southeast Alaska.

He uses the Happywhale database to identify the whales he measures.

Van Aswegen said the lack of food sources during the marine heatwave 'led to a decline in fertility in 2018'. There are only three baby humpback whales that swim from Hawaii to Alaska. At the end of the feeding season, all three animals went missing.

During the shorter marine heatwave that devastated the northeast Pacific in 2021, Van Aswegen found that on average, 24 mother whales lost weight after the hunting season. Meanwhile, normally, these mother whales will gain about 16 kg per day.

"We have never seen nursing females lose weight in (such) hunting grounds ," Van Aswegen said.