Research shows reduction in cold water habitat means more whales will be trapped in nets
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Humpback whales are more likely to get entangled in fishing gear in years when rising ocean temperatures make it difficult to find habitat in cold waters, according to new research published Wednesday.
The findings are based on research conducted by the National Oceanic and Atmospheric Administration off the U.S. West Coast published Reduction in cold-water habitat is a greater cause of entanglement risk than increasing numbers of humpbacks, the researchers said in the peer-reviewed journal PLoS Climate.
The cold-water habitat is important for species like the humpback because it creates an “explosion of life” where krill and small fish like whales thrive, explains Geoff Shester, a senior scientist at the ocean conservation society Oceana, who was not involved in the research.
This beneficial cold water comes from the depths of the ocean, but it can be pushed down or compressed by marine heat waves associated with climate change, leaving limited areas available for food, Shester said. This is known as housing compression.
When those areas overlap with areas that are open to fishing, “it’s basically creating a perfect storm of a lot more interactions between the whale and where it has fishing gear,” Shester said.
Warming waters off the US west coast could lead to more humpback whales getting caught in fishing gear, scientists say. He says the areas of cold water in which the animals normally thrive are shrinking, forcing them closer to shore.
According to Andrew Trites, director of the Marine Mammal Research Unit at the University of British Columbia, this could be particularly harmful to humpbacks.
“Humpbacks, unfortunately, when they get stuck in something, they have a tendency to roll over and they can wrap themselves up so tightly that they’re unable to get out of it. All they can do is keep tugging on it until it frees them by biting the flipper or humans come to intervene,” he said.
“When we find them – and we don’t find them all – many die horrible, tragic deaths.”
US researchers found that before 2014, 10 or fewer humpback entanglements were typically reported on the West Coast. This tripled to 31 in 2024, and reached a high of more than 40 during major marine heatwaves known as “the Blob” in 2015 and 2016.
NOAA scientist Jarrod Santora and colleagues analyzed the relationship between humpback entanglements, population size, and changes in cold-water habitat reported on the West Coast over 25 years.
They found that humpback entanglement occurred more frequently during years in areas with less cold-water habitat and that population growth alone was not enough to explain the increase statistically.
US researchers have created a tool called the Habitat Compression Index, which they say can predict the state of the ocean six to 12 months in advance.
Shester explained that the index is an important tool because it identifies times and places when there is a higher risk of entanglement and allows decision makers to close fishing in those areas. The index is already in use in California, he said.
There have also been technological advancements like ropeless fishing gear that could help moving forward, Shester said.
“Fishermen are now moving back to these areas that are closed with fishing gear that does not pose the risk of entanglement.”
