Climate change is the silent force behind a sudden decline in the North Atlantic right whale population, according to a new study backing a growing body of research into why endangered animals have swung from slow recovery to alarming decline.

An analysis of data on plankton, oceanic conditions, and whale sightings published Wednesday in Oceanography magazine showed that whales abandoned their traditional feeding grounds in the Gulf of Maine in 2010, the same year the water warmed the fat Crustaceans that eat them caused tumbling in the area.

Many of the whales eventually followed their food north to the Gulf of St. Lawrence, but the gear and ship protection that had protected them in their previous habitat did not exist in their new one. Entanglement in fishing gear is the leading killer of North Atlantic right whales, followed by collisions with ships.

“They were moving so fast that our guidelines didn’t match them,” said Erin Meyer-Gutbrod, a quantitative marine ecologist at the University of South Carolina and one of the study’s authors. “The environment is just not as predictable as it used to be, so I think we all need to think more on our own.”

To make matters worse, the researchers found that the decline in crustaceans had led to a decline in reproductive rates. “We’re slowing down their births and we’re increasing their deaths,” said Dr. Meyer-Gutbrod. “You don’t have to be a super mathematician to guess what this change will make.”

Scientists counted only 356 people.

The research helps explain why the death toll increased in 2017, leading marine mammal officials to declare an “unusual death event” that is still in force. The whales tend to get caught in ropes that are used for crab and lobster fishing. The ropes can drown them, sever body parts, or cause slow death from impaired eating or swimming.

Canadian officials have responded by adding protective measures in the Gulf of St. Lawrence, including speed restrictions on ships and temporary closures of certain fisheries if a whale is detected. On Tuesday, NOAA Fisheries announced new rules for catching lobster and jonah crab in American waters, aimed at reducing the number of lines that fall from marker buoys. They also weaken the lines so that tangled whales can break free.

Conservationists reacted with disappointment to the long-awaited rules, criticizing them for falling short of what the whales need.

The most effective solution, according to the study’s authors, would be to switch to ropeless fishing gear. “That would have a huge impact,” said Charles Greene, Senior Fellow at Ocean Visions. a research and advocacy group and one of the authors of the study.

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Fishermen fear that such gear is too expensive and less efficient. Activists and researchers say the key is making the equipment attractive to them.

“We need to figure out how to properly fund it so that they can make this technological shift,” said Dr. Greene, former professor at Cornell University’s Department of Earth and Atmospheric Sciences. “That got people to install their houses on the roof with solar energy.”

Various speed limits exist in United States’ waters to keep whales from colliding, but operators often disobey the rules, according to research by the nonprofit Oceana.

Perhaps 10,000 right whales swam the North Atlantic before the advent of widespread whaling. According to the International Whaling Commission, they were considered good hunting targets because they moved slowly, got stuck close to the shore, and swam dead, while at the same time supplying copious amounts of oil and beards. In the 1890s, the species was hunted close to extinction. But whale numbers slowly recovered after the ban on commercial whaling, reaching around 500 before the current decline began.

Previous research suggested that the loss of plankton and warming of the water caused the whales to move, but this study represents the strongest case yet that human-made climate change is reducing that prey, the whales moving to new areas and has led to a decline in reproduction rates.

“While worrying about the ultimate threat the whales have faced, it is not surprising that they appear to be moving north in response to these changes,” said Jaime Palter, professor of oceanography at the University of Rhode Island. who was not involved in the study.

Conspicuous calluses on the heads of the whales have enabled researchers to document each and every individual.

Although their natural lifespan is around 70 years, when the dead are found they are inevitably much younger. The latest victim was an 11-year-old man named Cottontail, who was found dead off the coast of South Carolina in February. Researchers had been chasing him since October when he was found entangled with his head and mouth in a line that pulled three or four lengths behind him.

There is hope for the whales, scientists say. Nineteen calves were born this year, more than any year since 2013. Dr. Meyer-Gutbrod said she thought her mothers somehow found more food.