Study: Climate change could negatively impact 65% of humpback whale breeding grounds this century

File Photo: E. Lyman – HIHWNMS NOAA Permit 14682

Findings from a collaborative study and subsequent scientific paper underscore the need for governments to focus on protecting critical ocean habitats, such as whale breeding grounds.

The study examines climate change scenarios over a 100-year period to project the potential impacts of rising sea surface temperatures on the breeding grounds of humpback whales.

High-Resolution Projections of Global Sea Surface Temperatures Reveal Critical Warming in Humpback Whale Breeding Grounds, was published in Frontiers in Marine Science and written by PhD student Hannah von Hammerstein (Department of Geography and Environment, University of Hawai’i at Mānoa). Co-authors include: Jens J. Currie, PWF Chief Scientist, Stephanie H. Stack, PWF Chief Biologist, Renee O Setter, PhD Student (Department of Geography and Environment, University of Hawaii at Mānoa ) and Martin van Aswegen (Marine Mammal Research Program, Hawai’i Institute of Marine Biology, University of Hawai’i at Mānoa).

File photo courtesy of J. Moore – HIHWNMS/ NOAA (MMHSRP Permit #20311)

“Our goal was to refine our understanding of how climate change affects humpback whale breeding grounds while producing results that can benefit the protection of humpback whales worldwide,” von Hammerstein said. in a press release, adding that coral bleaching and coastal erosion due to sea level rise are already visible along the coasts of the Hawaiian Islands. “Hawai’i, a place rich in biodiversity, is one of the few places in the world where humpback whales gather each year to breed.”

The study notes that each winter, humpback whales travel thousands of miles to mate and give birth in the ‘Au’ Channel off Maui and other tropical coastal waters in regions where surface temperatures of the sea vary between 21 and 28°C.

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“As anthropogenic emissions of greenhouse gases trigger global climate change and warm the oceans at an unprecedented rate, sea surface temperatures in some of these tropical regions could exceed the normal range in the next century. Although global projections of sea surface temperatures exist and are a crucial tool for documenting the collective effects of climate change, they lack the detail and resolution to effectively analyze and predict the regional temperature patterns needed to project changes. in humpback whale breeding grounds,” according to the PWF.

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To better understand and anticipate the effect of climate change on regional sea surface temperatures, the researchers say the collaborative research team produced large-scale projections of climate variables.

Using statistical analyses, the team projected sea surface temperatures around the world in each decade and illustrated the shifting of the 21 and 28°C isotherms, which border the temperature envelope. preferred breeding and calving grounds for humpback whales over the current century.

“The analysis was originally undertaken as a class project by doctoral students at the University of Hawai’i at Manoa. They came up with the idea to apply their method to humpback whales and measure changes in the ocean,” Stack said. “To pursue this idea, they invited co-authors from the UH Marine Mammal Research Program and the PWF research team to join the project and contribute their knowledge of humpback whales to help interpret climate projections.”

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By mapping the future trajectories of two climate change scenarios, the study found that 35% of humpback whale breeding grounds will experience temperatures above or below 1°C of the 28°C threshold if social, economic and current technologies continue (‘average greenhouse gas trajectory).

Under the scenario describing rapid economic growth in carbon-intensive industries (the greenhouse gas trajectory of “fossil-powered development”), the number of breeding grounds affected increases dramatically to 65%, according to the study. Researchers say: “If breeding grounds exceed 28°C, whales could stop using these areas, which could not only jeopardize whale breeding rates, but also inflict economic hardship on countries that depend on tourism. whaler.

“This project was a computer simulation of what the ocean will look like over the next 100 years. It was conducted by feeding existing climate and emissions data to a computer model to project future changes and impacts on humpback whale migration,” Stack said. “It wasn’t a field study, which means we didn’t measure actual changes in the ocean or whale populations.”

According to PWF researchers Currie and Stack, this case study supports the need for global governments to focus on protecting critical ocean habitats by collectively reducing global greenhouse gas emissions, minimizing further temperature increases and providing high-resolution climate data to preserve the ecological integrity of the humpback whale. whale breeding grounds around the world.

“This is just the beginning,” Stack concluded. “PWF’s research program will continue to study the main threats to cetaceans, including climate change, to better understand their impact on the migration of great whales as well as the management measures that offer the best protection against these threats. .”