When a North Atlantic right whale swims into a submerged net or rope, it panics and rolls. This makes everything worse, tangling the fishing gear in the animal’s mouth or tightly wrapping it around the flippers or tail.

For a smaller cetacean, this might mean instant death. But for right whales, entanglement is a far more uncertain affair.

Adults can reach lengths of 50 feet and weigh more than an Abrams tank. They are monstrously powerful, which means that a right whale can sometimes blast its way free from entanglement. Other times, the whales escape death but continue to drag around ropes, hooks, anchors and even entire sets of lobster traps, for days, months or years.

This is what’s called a chronic entanglement, and while it’s obvious that hauling all this extra weight around can’t be good for the whales, it’s been extremely difficult for scientists to quantify the physical toll it exacts. Doing so is important, however, because entanglements have risen to become the leading cause of death for endangered North Atlantic right whales.

That’s where poop comes in. In a recent paper in the journal Endangered Species Research, scientists showed for the first time that right whale stress hormones can be accurately measured by sifting through the animals’ feces. And they found that chronically entangled right whales show stress levels that are orders of magnitude greater than unencumbered whales.

“It’s really the first time that we’ve been able to look at the internal health of large whales,” said Elizabeth Burgess, a marine biologist at the Anderson Cabot Center for Ocean Life at the New England Aquarium. “So it’s quite groundbreaking just in that alone.”

The findings add to a growing body of research demonstrating the deleterious effects of human activity on whales. A study published Thursday in the journal Science showed that narwhals’ hearts nearly shut down after they’re caught in fishing nets. Another recent paper provided evidence that man-made noise causes beaked whales to use up their oxygen stores faster while diving.

Understanding the plight of right whales in the North Atlantic is particularly critical because only 500 or so remain in those waters, and 83 percent of the animals sport scars indicative of entanglements, Burgess said. Half of those show signs of having been entangled more than once.

“We’ve lost 17 whales this year,” Burgess said. “And we’ve only had five calves born into the population.”

Burgess and her colleagues figured important information might lie in the animals’ feces. All vertebrates produce specific hormones when they’re undergoing physical or emotional stress, said Craig Harms, a veterinarian at the North Carolina State University’s College of Veterinary Science, and these stress hormones can be detected in both blood and saliva.

“This has been very well documented in wider things, like college students during an exam period,” said Harms, who co-authored the study.

The thing is, you can’t just go up to a 70-ton animal fighting for its life and draw a blood sample. (The dangers of such an approach were vividly illustrated earlier this year, when Joe Howlett, the founder of the Campobello Whale Rescue Team, was struck and killed by a right whale off the coast of Canada just moments after freeing it from a mess of fishing gear.)

But right whale poop, which would also contain stress hormones, is easier to procure. It floats for a while after the animal does its business. What’s more, dogs can be trained to ride around on boats and sniff out these samples. That means all the scientists have to do is lower a dip net into the water and scoop up the waste.

When all was sniffed, bagged and tagged, Burgess and her colleagues had rounded up fecal samples from a half-dozen right whales in chronic entanglements; five more that had been killed by vessel strikes; 113 healthy, free-swimming whales; and one unlucky animal that had shed its entanglement but suffered permanent damage to the spine, causing it to eventually strand on a beach. (Harms was the one with the unenviable task of euthanizing the doomed creature.)

From these samples, they learned that right whales undergoing chronic entanglements show stress levels about 30 times higher than healthy whales. Interestingly, the study also showed that animals cleaved by ships did not present stress hormones in their fecal matter, probably because they died too quickly for the markers to show up.

Burgess hopes monitoring of stress hormones in right whale feces will give researchers a sort of early warning system that signals when the population is in trouble but before widespread deaths, strandings or drops in reproduction. Changes in hormone levels, for example, might point to something going on in the environment — noise, pollution, food scarcity — that people could try to remedy.

When it comes to North Atlantic right whales, one thing could potentially save lives overnight: Getting fishermen to switch to a different kind of rope. According to Amy Knowlton, a research scientist at the Anderson Cabot Center who was not involved in the study, ropes are now much stronger than they used to be.

Many commonly used fishing ropes are around the 3,000- to 4,000-pound “breaking strength,” and some go up to 12,000-pound breaking strength. Knowlton said she suspects this is one reason entanglements have overtaken vessel strikes as the leading cause of death for North Atlantic right whales.

“We ask that the fishing industry consider using 1,700-pound breaking strength rope or less, because that reduced strength will give the whales a better chance of breaking free from that gear,” Knowlton said.

It’s also likely more whales die of entanglements than we realize. Knowlton works with the North Atlantic Right Whale Consortium to identify individual whales based on photographs, and sometimes they’ll receive a sighting of a whale tangled in fishing gear once and then never see that animal again.

“They just disappear,” she said.

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