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Marine mammals in U.S. waters are highly vulnerable to climate change

In a recent study, researchers have discovered that a staggering 72% of cetacean and pinniped stocks under U.S. jurisdiction exhibit high or very high vulnerability to the threats posed by climate change. The main threats to these marine mammals include rising ocean temperatures and changes in water composition.

Pinnipeds are “flipper-footed” animals such as seals, sea lions, and walruses, while cetaceans are species that cannot survive on land, including whales, dolphins and porpoises.

Climate change and marine mammals

The study, led by Matthew D. Lettrich from NOAA Fisheries, sheds light on the susceptibility of marine mammals in US waters to the ever-intensifying impacts of a changing climate.

Several factors drive this vulnerability. As the Earth’s climate undergoes rapid alterations, the distribution, behavior, and movements of marine mammals are being significantly influenced. 

Key agents of this change include warming ocean temperatures, diminished sea ice cover, increased ocean acidity, changing salinity levels, and declining dissolved oxygen.

Focus of the study 

Until now, while Climate Vulnerability Assessments (CVAs) provided insights into the climate impacts across a spectrum of species, none had specifically delved into US-managed marine mammals. 

Recognizing this gap, the researchers embarked on a comprehensive assessment of 108 marine mammal stocks spanning the western North Atlantic, Gulf of Mexico, and Caribbean Sea. 

The goal was to gauge their exposure to climate change and their inherent ability to adapt to its consequences.

To do this, the team used 16 climate-related factors that are likely to influence marine mammals directly or indirectly via their prey or habitat. 

Alarming results for marine mammals

The assessment revealed that a startling 44% of marine mammal stocks were found to have a “very high” climate vulnerability score. Baleen whales, medium-sized whales, toothed whales, and dolphins were found to have the greatest risk.  

The primary culprits affecting these species were identified as alterations in ocean temperature, acidity, and dissolved oxygen levels, which have direct repercussions on their prey availability and habitat conditions.

Changes in sound transmission 

Moreover, a less explored facet of climate change impacts on marine mammals is the changes in sound absorption and transmission in waters due to fluctuating pH and temperature levels. 

This has significant implications for species that rely on echolocation for activities like communication, hunting, and foraging.

Ecosystem management and conservation

“These results provide information for researchers, managers, and the public on marine mammal responses to climate change to enhance the development of more effective marine mammal management, restoration, and conservation activities that address current and future environmental variation and biological responses due to climate change,” wrote the study authors.

“This vulnerability assessment provides a tool that can complement other marine mammal assessment techniques and support the broader implementation of protected species and ecosystem management and conservation as the climate changes.”

The researchers would like for the marine mammal climate vulnerability assessment to be repeated when enhanced input data is available, such as higher-resolution climate projections and better species-specific biological information.

“Using a systematic approach allowed us to look across all of these stocks and better understand what drives their vulnerability to climate change,” said Lettrich.

“We can now go out and look at some of these individual responses to climate change, and explore approaches to reduce the impacts of climate change on these vulnerable populations.”

The research is published in the journal PLOS ONE.

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