Marine Heat Wave Linked to Sharp Increase in Whale Entanglements

An ocean heat wave off the U.S. West Coast from 2014 to 2016 drove humpback whales into a narrow band of cooler water, leading to a dramatic increase in whale entanglements with crab-fishing gear, according to a new study.

Researchers at the federal Southwest Fisheries Science Center examined the causes of the spike in whale entanglements off the West Coast in 2015 and 2016. They discovered that a large area of warm water, known as “the blob,” shrunk the suitable feeding habitat for humpback whales. The whales forage in cooler, nutrient-rich waters that support abundant populations of krill and anchovies.

The large expanse of warm water off the West Coast drove the prey, and the whales, into a much smaller area of cool water near the coast, where Dungeness crab fishermen place much of their gear. As a result, confirmed whale entanglements rose from 10 in 2014 to 53 in 2015 and 55 in 2016, according to the study, published in the journal Nature Communications.

The study’s authors said that the spike in entanglements has prompted state and federal fisheries managers and scientists to work together to avoid another spate of whale entanglements during future ocean heat wave events. Among other things, fishermen and managers have formed a California Dungeness Crab Fishing Gear Working Group to monitor marine heat waves and whale movements, and alter fishing practices to keep the whales away from crab gear.

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