The wolf was neither shot nor poisoned, according to a necropsy. No one can say for sure how or why it died, according to U.S. Fish and Wildlife Service biologist John Stephenson. But the animal was visibly lean and had a wound on one of its front paws. And given that a baited leg-hold trap was used to catch the wolf, it’s possible that the capture contributed to the wolf’s demise, officials said.

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The Oregon wolf was not the first animal to die after being captured for study. Three pronghorns perished this month as the result of a relocation effort in Arizona. A vaquita, one of the few remaining members of its porpoise species, died in 2017 as scientists attempted to capture it for a captive-breeding program. A wild cat dubbed Macho B — one of the last jaguars known to cross the U.S.-Mexico border — was euthanized after its health declined following a capture in 2009.

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Scientists are capturing and tagging more wild animals than ever, using technologies that allow them to keep tabs on everything from honeybees to great white sharks, and they say casualties are extremely rare. But each high-profile death raises questions about the toll these operations inflict — especially when they are carried out in the name of conservation or the animals’ well-being.

“An individual animal is never better off because we trapped it or caught it or tagged it,” said Steven Cooke, a biologist at Carleton University in Canada who has published several papers urging caution and consideration when capturing and tracking wild animals. “But the knowledge gained from that individual can hopefully be useful for informing how to better manage, conserve, protect and restore populations and species.”

Several things could have gone wrong for the Oregon wolf. The paw injury might have prevented it from finding enough food, for instance. But the stress of capture itself — from being immobilized in a trap, or chased over long distances — can also kill.

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This kind of death is caused by a condition called capture myopathy, which occurs when overworked skeletal muscles — the ones that power the fight-or-flight response — start to break down and release a protein called myoglobin. In great amounts, myoglobin can enter the bloodstream and concentrate in the kidneys, where it causes tissue damage and sometimes kidney failure.

Cooke regularly captures fish for his work, and he said even those that are not bleeding or in obvious distress are affected in some way. A simple dip net removes the natural layer of slime that protects fish and can cause micro-injuries, including frayed fins. That damage must be taken into account before any study or wildlife management action that requires catching or handling, he said.

Such knowledge was put to use recently in Florida, where the state Fish and Wildlife Conservation Commission voted to update fishing guidelines, based in part on research showing improper handling can cause sharks massive stress and even death. Some species, such as the great hammerhead, may be particularly susceptible to this kind of trauma. But to understand why, scientists first had to capture various shark species and measure their physiological responses.

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“All conservation work is going to cast some type of shadow,” said Austin Gallagher, who has studied hammerheads and serves as chief scientist and CEO at a nonprofit group called Beneath the Waves. “This is something we all know and accept when going into any research project.”

Responses to capture also vary among land animals. One study found that 3.4 percent of gray wolves suffered capture-related mortality over the course of a long-term research project but that fewer than 1 percent of moose and brown bears met the same fate.

Part of this may have to do with capture methods. Bears can be easily lured into a culvert trap baited with doughnuts. Mountain lions, on the other hand, are usually too wary to walk into what amounts to a large metal tube.

“Mountain lions are truly the ghosts of the forest,” said Jim Williams, a biologist with Montana Fish, Wildlife and Parks and author of “Path of the Puma.”

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The traits mountain lions have evolved to make themselves invisible to prey also make them extremely difficult to catch. This is why most biologists rely on trained scent dogs to chase a cat into a tree — no doubt a stressful event for the lion. Once the scientists catch up, they tranquilize the cougar, then lower it to the ground by rope.

Capturing large ungulates, such as bighorn sheep, may be more intense still. Williams said scientists often approach the animals by helicopter and immobilize them with guns that fire nets.

“So there are a whole bunch of techniques that can be used to capture and handle wildlife, and each one of those techniques comes with different risks — for both the people and the animals,” Williams said.

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Researchers insist their work is vital for understanding how animals respond to capture. That can be useful when scientists or wildlife managers must relocate an animal, such as a grizzly bear that ransacks campsites for food. In extreme cases, they say, knowing how to safely catch and handle a species might be necessary for saving it from extinction.

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Take the vaquita. There may be as few as 30 left. The small porpoises live only in the Gulf of California, and their habitat is laced with illegal nets meant for a fish called totoaba. The vaquitas’ prospects have become so bleak that an international team decided in 2017 to try to round up the few that remained and begin a captive-breeding program.

The plan was risky from the outset. The animals were known to be extremely skittish around people, and no one had ever kept a vaquita in captivity before.

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To prepare, scientists looked to information gleaned from the vaquita’s cousins. Two other porpoise species had been found to do well in captivity, said Barbara Taylor, a conservation biologist who leads the National Oceanic and Atmospheric Administration’s Marine Mammal Genetics Group. A third did not.

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Unfortunately, vaquitas turned out to be more like the latter. When the team captured two females and transported them to holding tanks, cortisol and other stress hormones flooded their bloodstreams and their behavior was clearly agitated and panicked. The scientists quickly decided to return the animals to the ocean, and one swam away, but the other suffered a cardiac arrest beside the boat. For three hours, the team kept the animal alive by performing the marine-mammal equivalent of CPR, but the vaquita never resumed breathing on its own.

“All of us knew she was essentially dead,” said Frances Gulland, a veterinarian and commissioner at the U.S. Marine Mammal Commission who was involved. “We all knew that the moment we actually declared her dead, it wasn’t just declaring an individual dead, it was sort of declaring a species gone, too.”

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In the end, Gulland made the call to let the animal die, a moment she described as “overwhelmingly depressing” — perhaps more so because it might have been avoided. With more time or more vaquitas, she said, researchers might have developed a capture protocol that accounted for the animal’s risk-averse biology.

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But in other instances, capturing animals and raising them in captivity have saved species from the edge. The California condor and whooping crane are two well-known examples. One day, the Sumatran rhino may join them.

With 80 or fewer Sumatran rhinos left in the wild, an international coalition of conservation organizations recently announced a last-ditch effort to capture as many as possible and begin a breeding program.

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A similar strategy has failed this species once before. After scientists caught 40 rhinos in the 1980s and 1990s, three animals died of injuries suffered in the traps and eight others died prematurely while in captivity.

The effort was “billed as an absolute disaster,” said Barney Long, director of species conservation at the nonprofit Global Wildlife Conservation. But it also resulted in two Sumatran rhinos being sent to the Cincinnati Zoo, where, over the course of the next decade, scientists solved the mystery of how to get the animals to breed.

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“What seemed like a failure 20 to 30 years ago is now probably the only thing setting up an opportunity to save the species from extinction,” Long said.

The coalition says it will review ways to mitigate risks while capturing and transporting the rhinos. In November, the same groups successfully trapped a Sumatran rhino and then mildly sedated it to keep it from thrashing about and injuring itself. A military escort and a logging-company bulldozer helped make the long trek out of the jungle as swift as possible.

“Safety of the animals and the people involved are of paramount importance,” said Susie Ellis, executive director of the International Rhino Foundation. “There’s no room for error now.”