Marine mammals in the Arctic and Subarctic are suffering from increased mortality, reduced reproduction rates, and heightened vulnerability to disease due to marine heatwaves (MHWs), according to a new study.
MHWs are periods of significantly elevated sea temperatures lasting from days to years, and the Arctic Ocean is predicted to be a future hotspot for such events. These temperature spikes can cover vast areas, ranging from a few kilometers to thousands.
The study analyzed MHWs in the Bering and Barents Seas key pathways to the Arctic Ocean focusing on the 2017-2019 MHWs in the Bering and Chukchi Seas and the infamous 2014-2016 “Blob” in the northeast Pacific.
Marine mammals like whales and sea lions often show delayed responses to MHWs due to their higher mobility and blubber reserves, which buffer them from immediate food web disruptions. However, that same blubber can hinder heat dissipation for species like narwhals and bowhead whales, posing direct risks as water temperatures rise.
The study highlighted high mortality events, such as humpback and fin whale deaths during the Gulf of Alaska MHW. Toxic algae blooms and diseases linked to these heatwaves have also contributed to marine mammal deaths, including the first recorded polar bear fatality from avian influenza in 2024.
Long-term impacts include low calf production and distributional changes that increase risks like entanglement in fishing gear. For species like spotted seals, extended warm periods have led to high mortality and weakened pups.
Some Subarctic species may migrate farther north to escape warming, but year-round Arctic residents lack that option, making them especially vulnerable.
The study, published in Frontiers in Environmental Science on February 19, underscores the severe consequences MHWs have on Arctic ecosystems and highlights the urgent need for climate mitigation to protect these species.