Ocean heatwave caused record number of whale entanglements

Climate change-induced ocean warming was partly responsible for record numbers of whale entanglements in US fishing nets during 2015 and 2016, according to a new study. Researchers investigating the 2014-2016 northeast Pacific marine heatwave found that food scarcity led the mammals to forage closer to the shore, where they became entangled in crab fishing nets. The researchers have called for new measures to alert fishermen and fishery managers to the likelihood of entanglement, and are also developing a website that will forecast areas off the US west coast where whales are most likely to feed.

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Why does this matter? This “habitat compression” phenomenon is another significant event attributed to the 2014-2016 marine heatwave, otherwise known as “the blob”, with a separate recent study also linking it to the death of a million North Pacific seabirds – the largest avian mass mortality event ever recorded.

The blob (which has recently shown signs of re-emergence) was the result of a confluence of atmospheric activity, enhanced by the El Nino ocean-atmospheric phenomenon. Its effects were widespread and continue today. These types of marine heatwaves are expected to increase in both frequency and intensity, as climate change continues to raise the amount of heat absorbed by the world’s oceans.

The humpback whale entanglements, which remained prevalent over subsequent years, are one element of a series of environmental problems facing California’s commercial crab and other fisheries. Frequent algal blooms led a coalition of commercial fishers to bring a lawsuit against fossil fuel firms in 2018. And a study last year found California waters are acidifying at twice the rate of the global average, which has its own recently reported significant impacts on crabs’ and other species’ ability to form shells.

Aside from taking widespread action on climate change to protect the world’s oceans – without which events like the blob are set to become the new normal – for the time being the crab industry and humpback whales may have to learn to be bedfellows.

The start of the crab fishing season was delayed last year to help protect the animals. The multidisciplinary California Dungeness Crab Fishing Gear Working Group has also been established to work on effective crab fishery management. And the researchers behind the Nature study are developing a website which will use oceanographic data to forecast where whales are most likely to feed off the West Coast, so fishermen can react accordingly.

Sources: Nature Communications

The Independent