Climate change is increasing the frequency and severity of marine heatwaves — warm water anomalies that disrupt marine ecosystems, and this creates new challenges for fisheries management and ocean conservation.
A new study shows how the record wave of sea heat 2014–2016. caused changes along the West Coast of the United States, which led to an unprecedented increase in the number of whales that became entangled in fishing gear.
“With the warming of the ocean, we have seen a shift in the ecosystem and in the eating behavior of humpback whales, ” said Jarrod Santora, an applied mathematics researcher at the University of California at Santa Cruz and the first author of a study published on January 27 in Nature Communications.
Santora, which is also associated with the Fisheries Science Center, uses marine ecosystem models to inform fisheries management and conservation. As a scientific consultant to a working group convened to solve the problem of whale entanglement, she provided reports to state and federal agencies to help them make managerial decisions that can reduce the risk of entanglement of living things.
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Work on a solution to the problem
“It was a series of events over these three years, but now we have the opportunity to prevent a recurrence of this, ” Santora said. - We have developed a risk assessment and mitigation program, conduct aerial surveys and provide ecosystem indicators to public resource managers so that they can make informed decisions. A huge group of people is working on it. ”
“The high productivity of the California Current is supported by a wind lift of cool, nutrient-rich water along the coast that supports large prey populations (such as krill, anchovies and sardines) that attract whales and other predators. The intensity of upwelling and the degree of cool enriched water off the coast vary from year to year, but extreme warming in 2014-16. (which became known as the “warm spot”) squeezed this primary habitat into a very narrow strip along the coast, ”Santora explained.
Humpback whales are fed in Monterey Bay. Changes in the ecosystem caused by ocean warming can lead to greater “conflict” between feeding whales and crab equipment, increasing the risk of entanglement.
The number of accidents has increased
This shift brought an unprecedented number of whales to areas where they were more likely to encounter crab gear. Whale entanglement, which averaged around 10 per year until 2014, reached 53 confirmed entanglements in 2015 and remained high — 55 confirmed entanglements in 2016.
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A further complication of the situation was another consequence of the warm sea wave, the unprecedented flowering of toxic algae along the West Coast. When scientists discovered dangerous levels of domoic acid - a neurotoxin - in Dungeness bays, the opening of the 2015-16 crab fishing season. was delayed until the end of March 2016. Typically, crab fishing activity is highest in November and December, but in 2016, the peak fishing activity coincided with the arrival of migratory whales from California in April and May.
“All this equipment went out of order right at the peak of the arrival of the whales, so it’s even worse, ” Santora said.
Another factor, she said, is the ongoing recovery of whale populations. Conservation efforts that began in the 1960s allowed many populations that were destroyed by commercial whaling to begin to return. Although some humpback whale populations in the North Pacific are still considered endangered, their total numbers are increasing.
Mutually beneficial cooperation
According to Santora's environmental expert, the events of 2014-16. show how important it is for scientists to collaborate closely and communicate clearly with fisheries managers and other stakeholders. One of the positive outcomes of the crisis was the creation of a crab fishing working group in California, which included commercial fishermen who manage state and federal resources, conservationists and scientists. The group has developed a risk assessment and mitigation program to support collaborative efforts to reduce entanglement during global warming.
