Ocean Warming: Marine Heatwave Affects Whales, Which Leads to Entanglement

Climate change is allegedly rising the regularity and severity of marine heatwaves, which is warm water deviations that interrupt marine ecosystems, creating, in turn, new difficulties for fisheries management and ocean conservation.

A new paper depicts the way record-breaking marine heatwave of the years 2014 to 2016 created alterations along the U.S. West Coast that conduced to an unusual increase in the numbers of whales that became tied 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 scientist in applied mathematics at UC Santa Cruz and first author of the research, published in the journal Nature Communications.

Warm Temperatures Affects the Marine Life

Santora utilizes data-focused models of marine ecosystems to notify fishery management and conservation. He has been offering his observations to state and federal agencies to help them make management decisions that can decrease 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 efficiency of the California Current is backed up by wind-caused upwelling of cool and rich in nutrient water throughout the coast, which maintains massive populations of prey that attack whales and other predators.

The vehemence of upwelling and the degree of cool abundant water along the coast differs from year to year, but the violent warming event from 2014 to 2016, also known as the ‘warm blob,’ compacted this prime habitat into an incredibly small band along the coast, Santora said.

“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.”

Fewer Entanglements

The change brought an unprecedented number of whales into regions where they were more prone to come across crab fishing equipment. Whale entanglements, which totaled about 10 per year previous to 2014, spiked to 53 confirmed entanglements in 2015, and stayed high at 55 confirmed cases in 2016.

Another agent, Santora said, is the ongoing recovery of whale populations. Preservation attempts that began in the 1960s have allowed numerous populations that were killed by commercial whaling to start making a return.

There is now a Risk Assessment and Mitigation Program in place that supports collaborative attempts to reduce whale entanglements.

“Nobody wants to entangle whales,” Santora said. “People are working to develop ropeless gear, but the broad application of that new technology is still far in the future. For now, the best we can do is to monitor the situation closely and get ecosystem science information to the people who need it.”

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