The long-term study, published Thursday in the journal Current Biology, estimated that a calf born in recent years was likely, at maturity, to be about 3 feet shorter than those born in the 1980s. have become more problematic for whales in recent decades, as ropes have increasingly used synthetic materials and have become stronger.

“Stunting is a classic sign that a species is in trouble,” said Michael Moore, senior scientist at the Woods Hole Oceanographic Institution and co-author of the study. “Smaller dams are less able to be successful breeders because they have a smaller fuel tank and less lactation. This is the biggest concern.

He and other authors said the findings call into question a long-awaited report released last month by the National Marine Fisheries Service which found that the lobster industry was not putting the survival of right whales at risk. Last year, a federal judge ordered the agency to produce the report, known as the biological opinion, after ruling that it had violated the endangered species law by failing to reduce tangles.

The agency’s controversial “no danger” finding means that lobster boats and other trap fishermen can continue to use vertical buoys, the ropes that extend from the surface to the seabed, which are the primary source of tangles. But if population and calving rates don’t improve, the industry will need to do a lot more to protect whales, which could lead to major changes to the fishery, like removing ropes from the water column. , the regulators said.

Maine officials have long been concerned about the potential impact of right whale protection on the lobster fishery, which contributes an estimated $ 1.5 billion to the state’s economy.

In a statement after the agency released the organic advisory, Governor Janet Mills said she was relieved regulators didn’t need action that could have effectively shut down the fishery, but she said the government’s findings and their potential “disturbing” ramifications.

Moore and other authors of the new study urged the federal government to reconsider their findings.

“The safe decision in the recent biological opinion should be reconsidered in light of this new evidence that the species has failed to thrive and has a stunted growth rate,” said Moore. “It is a major concern that the planned government management actions will be seriously insufficient. “

Amy Knowlton, senior scientist in the New England Aquarium’s Right Whale Research Program and also author of the study, said her findings suggest that regulators in the United States and Canada need to do much more to reduce the threat of disease. ‘tangle. In recent years, as the Gulf of Maine has warmed at an accelerating rate, whales have moved further north in Canadian waters in search of the rice-sized copepods on which they feed.

“I am very worried,” she said. “Things continued to get worse for right whales. “

The study, which measured 129 whales over 20 years, relied on high-resolution aerial photos of planes and drones to track their size.

Although the study found that tangles were the main cause of the whales’ decrease in size, which can reach 60 feet in length and weigh over 250,000 pounds, it also attributed some of the stunting to d ‘other factors, such as increased noise from maritime traffic and how climate change is altering the distribution of their food sources.

Scientists unrelated to the study said it underscored their concerns about “sub-lethal” threats to the species, such as the dragging of fishing gear over long distances. Heavy machinery consumes a significant amount of energy, reduces the fat stores they need to reproduce, and makes them more susceptible to various diseases. It can also inflict deep wounds and drown them.

A previous study of 70 right whale mortalities between 2003 and 2018 found that when a cause of death could be determined, nearly 60% had died from entanglements, mostly from lobster or crab buoy lines. This study also found that entanglement mortality had increased dramatically over the past 50 years.

“Sublethal impacts should be taken just as seriously as direct impacts, such as collisions with ships,” said Fredrik Oscar Christiansen, marine ecologist at the Institute for Advanced Studies in Aarhus in Denmark, who said the results of the study of “tragic”. . “” This article really shows how harmful human disturbance can be to wildlife. “

Others have noted that the number of black calves born in recent years has been much lower than in previous years.

For example, between 2001 and 2005, 115 right whales were born; in the past five years, only 39 have been born, and at least three of them have already died.

Peter Corkeron, president of the Kraus Marine Mammal Conservation Program at the New England Aquarium, called the study “austere” and said it “conclusively demonstrates that entanglement is a major factor in the delay. growth “.

“This is yet another red flag on the gravity of the situation for North Atlantic right whales,” he said.

David Abel can be contacted at [email protected] Follow him on twitter @davabel.