Climate Change is Chasing Away Humpback Whales From Hawaii Waters

Due to climate change and rising greenhouse gas levels, or GHG, humpback whales may eventually steer clear of Hawaii waters, according to the findings of a recent paper by a team of researchers. Three graduate students from the University of Hawaii at Manoa make up the team: Renee Setter, Hannah von Hammerstein, and Martin van Aswegen from the Institute for Marine Biology's Marine Mammal Research Program and Department of Geography and Environment, respectively.

Humpback Whales

It is known that humpback whales migrate to tropical coastal waters, like those off the coast of Hawaii, where they give birth to their calves. The whales frequently return to the same locations each year in these regions, which have sea surface temperatures between 21 and 28 degrees Celsius.

The Possible Scenarios

Anthropogenic climate change, according to von Hammerstein, Setter, van Aswegen, and colleagues from the Pacific Whale Foundation, is heating the oceans at previously unheard-of rates. Over the course of the next century, some of these breeding grounds will likely reach temperatures higher than the 21-28°C range.

Increasing the resolution of global sea surface temperatures and monitoring the critical 21-28°C isotherms that surround humpback whale breeding grounds over the course of the twenty-first century. Isotherms are lines connecting points with the same temperature on a map or chart.

Two potential scenarios for climate change are presented by the research:

• In a worst-case scenario with continued high development and unabated carbon emissions, by 2100, 67% of humpback whale breeding grounds will have a sea surface temperature above the critical threshold of 28°C.
• That percentage would drop to 35% of breeding grounds in a "middle-of-the-road" scenario with international and global institutions working toward emission mitigation goals.

In some of the breeding grounds, critical warming was anticipated, according to von Hammerstein, but the sheer number of critically affected areas was unexpected. Even though the study's findings are sobering, they also show how the two emission scenarios differ and what can still be accomplished by taking emission mitigation measures.

Call for Global Effort

Setter continued to say that there needs to be a global effort to try to reduce greenhouse gas emissions and try to stay in that middle-of-the-road greenhouse gas emissions scenario at the very least, just so that saving many of those breeding grounds is possible from exceeding that critical temperature threshold.

Although it is currently unknown whether humpback whales will continue to migrate to breeding grounds above 28°C, the researchers note that they still hope that their findings will serve as motivation for policymakers to work toward reducing emissions, not only in Hawaii but also on a global scale.

Van Aswegen emphasized that while humpback whales are only one impacted species, their findings offer yet another illustration of what anthropogenic climate change will eventually bring. For mitigation measures to be implemented effectively and on schedule, our understanding of how ecosystems will change must be improved.