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As climate change becomes more severe in the coming decades, a range of impacts on the islands are expected: extreme coastal flooding, warmer temperatures, prolonged droughts, vulnerable coral reefs, hurricanes of greater intensity and impact.
Add a new possibility to the list: no humpback whales.
The findings of a new paper by researchers from the University of Hawaii and the Pacific Whale Foundation suggest that whales may one day avoid the relatively shallow ocean around the Hawaiian islands because the water will be too warm.
That could happen by the end of the century, the researchers say, if the fossil fuel industry is allowed to continue powering the global economy and generate unabated carbon emissions.
“We are imploring the public to think big and act now,” said Jens Currie, senior scientist at the Pacific Whale Foundation and one of the paper’s authors. “What we do today affects what will happen tomorrow.”
Currie, along with Pacific Whale Foundation colleague Stephanie Stack, and three UH Manoa graduate students — Hannah von Hammerstein, Renee Setter, and Martin van Aswegen — conducted the modeling study, which was published in the journal Frontiers in Marine Science in May.
It is estimated that more than 10,000 humpback whales travel from Alaska to Hawaii each year, where they breed and give birth primarily between December and April. The annual migration helps sustain a whale watching industry that is said to be worth more than $20 million a year to the state’s economy.
Humpback whale populations around the world migrate annually to tropical coastal waters like Hawaii, where sea surface temperatures range from 70 degrees to 82 degrees Fahrenheit. The whales usually return to the same places every year.
As greenhouse gas emissions warm the world’s oceans at an unprecedented rate, sea surface temperatures in these tropical regions are likely to eventually exceed the normal range for humpback whales.
Although projections of ocean warming are out there, they lack the detail and resolution needed to analyze and predict the regional temperature patterns needed to forecast changes in humpback whale breeding ranges.
To create detailed projections, the researchers used a statistical analysis known as the delta method to project sea surface temperatures around the world for each decade, highlighting shifting isotherms associated with preferred breeding and calving grounds over time the flow coincided century.
The analysis was originally conducted as a class project by von Hammerstein and Setter at UH Manoa, who invited UH Marine Mammal Research Program co-authors, including van Aswegen, and the Pacific Whale Foundation research team to help interpret the climate projections.
The research proposes two possible climate change scenarios:
>> By the year 2100, in a worst case scenario with unabated CO2 emissions, 67% of humpback whale breeding ranges will exceed the critical sea surface temperature of 82 degrees Fahrenheit.
>> In a “middle ground” scenario with global and international institutions working to reduce emissions, this number would fall to 35% of the hotbeds.
“We expected critical warming in some of the breeding areas, but the number of critically affected areas came as a surprise,” von Hammerstein said.
Currie said the whales could stop going to the breeding grounds if it surpasses 82 degrees because the warm habitat would affect breeding rates, cause chronic stress and affect the whales’ fitness.
Hatcheries with few or no whales could also create economic difficulties for countries that rely on whale tourism.
The researchers concede that while it’s not currently known whether humpback whales will continue to migrate to breeding grounds above 82 degrees, it’s very possible that they won’t.
Currie said studies suggest that in 2015 and 2016, when humpback whale sightings in Hawaii plummeted, the whales may have been discouraged from making the migration here due to a Pacific ocean heatwave known as The Blob.
“It was a possible glimpse into the future,” he said.
Currie said the researchers hope their findings will help spur policymakers to work towards reducing emissions.
“It’s really critical that we try to reduce our greenhouse gas emissions and really try to stay ‘in the middle of the road’ at least on that greenhouse gas emissions scenario,” Setter said.
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