Humpback whales may one day avoid Hawaiian waters due to climate change and rising greenhouse gases, according to a new study published in frontiers in marine science by a team of researchers including three University of Hawaii at Mānoa students—Hannah of Hammerstein and Renee Setter by the Department of Geography and Environment in the College of Social Sciences and Martin van Aswegen from the Marine Mammal Research Program at the Institute of Marine Biology.
Humpback whales are known to migrate toward tropical coastal waters such as Hawaii“>Hawaii‘s where they give birth to their calves. These areas are in regions with sea surface temperatures between 21 and 28 degrees Celsius (about 70–82 degrees Fahrenheit), and the whales typically return to the same locations annually.
According to von Hammerstein, Setter, van Aswegen and co-researchers at the Pacific Whale Foundation, anthropogenic climate change is warming the oceans at an unprecedented rate. At the current rate, it is likely that some of these hotbeds will heat up beyond the 21–28℃ temperature range over the next century.
Using a “delta downscaling” statistical method to increase the resolution of global sea surface temperatures and to trace the critical 21–28℃ isotherms (lines drawn on a map or chart connecting points of the same temperature) observed during Throughout the 21st century, research suggests two possible climate change scenarios:
- By the year 2100, in the worst-case scenario, with continued high development and unabated CO2 emissions, 67% of humpback whale breeding areas will exceed the critical sea surface temperature of 28℃.
- In a “middle ground” scenario, with global and international institutions working towards emission reduction targets, 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. “While the results of the study are discouraging, they also highlight the differences between the two emission scenarios and show what can still be gained by implementing emission reduction measures.”
Setter added: “It’s really critical that we try to reduce our greenhouse gas emissions and really try to at least stay on that ‘middle road’ greenhouse gas emissions scenario, just so we can cut as many of these hotbeds as much as possible.” from exceeding this critical temperature threshold.”
The researchers note that while it is currently unknown whether humpback whales will continue to migrate to breeding grounds above 28°C, they hope their findings could provide an incentive for policymakers to work towards reducing emissions, not just in Hawaii but also on an international level.
“Our results provide another example of what is to come with anthropogenic climate change, with humpback whales being just one species affected,” said van Aswegen. “Improving our understanding of how ecosystems will change is critical to the effective and timely implementation of mitigation actions.”
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