Member Highlight: Study Connects Marine Heat Wave With Spike In Whale Entanglements

2020-02-18T10:28:38+00:00 February 13, 2020|
(Credit: NOAA)

(Credit: NOAA)

Entanglements of humpback whales in fishing gear along the U.S. West Coast increased dramatically during the 2014 to 2016 marine heat wave known as the ‘warm blob.’

(From University of California Santa Cruz/ By Tim Stephens) — Climate change is increasing the frequency and severity of marine heat waves—warm water anomalies that disrupt marine ecosystems—and this is creating new challenges for fisheries management and ocean conservation. A new study shows how the record-breaking marine heat wave of 2014 to 2016 caused changes along the U.S. West Coast that led to an unprecedented spike in the numbers of whales that became entangled in fishing gear.

“With the ocean warming, we saw a shift in the ecosystem and in the feeding behavior of humpback whales that led to a greater overlap between whales and crab fishing gear,” said Jarrod Santora, a researcher in applied mathematics at UCSC’s Baskin School of Engineering and first author of the study, published January 27 in Nature Communications.

Santora, who is also affiliated with the NOAA Southwest Fisheries Science Center, uses data-driven models of marine ecosystems to inform fishery management and conservation. As science advisor for a working group convened to address the whale entanglement problem, he has been providing his analyses to state and federal agencies to help them make management decisions that can reduce the risk of entanglement.

“It was a perfect storm of events over those three years, but we now have the ability to prevent that from happening again,” Santora said. “We’ve developed a risk assessment and mitigation program, we’re doing aerial surveys, and we’re providing ecosystem-based indicators to the state resource managers so they can make informed decisions. There’s a huge team of people working on this.”

The high productivity of the California Current is supported by wind-driven upwelling of cool, nutrient-rich water along the coast, which sustains large populations of prey (such as krill, anchovy, and sardines) that attract whales and other predators. The intensity of upwelling and the extent of cool enriched water off the coast varies from year to year, but the extreme warming event in 2014-16 (which became known as the “warm blob”) compressed this prime habitat into a very narrow band along the coast, Santora explained.

“Predators that are normally more spread out offshore all moved inshore because that’s where the food was,” he said. “Krill populations always take a hit during warming events, but we started to see an increase in anchovy. Humpback whales are unique in their ability to switch between krill and small fish, so during those years they moved inshore after the anchovy.”

That shift brought an unusual number of whales into areas where they were more likely to encounter crab fishing gear. Humpback whale entanglements, which averaged about 10 per year prior to 2014, shot up to 53 confirmed entanglements in 2015 and remained high at 55 confirmed entanglements in 2016.

Further complicating the situation…

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