For an animal with an ivory appendage half the length of its body protruding from the top of its head, a narwhal moves in the water with surprising grace.

“It’s almost mesmerizing,” said Greg O’Corry-Crowe, a research professor at Florida Atlantic University who studies marine mammals. “The precision with which they wielded their tusks, it wasn’t like a broadsword. It was like a surgical instrument or the bow of a violin.”

In research published last month in the journal Frontiers in Marine Science, Dr. O’Corry-Crowe and colleagues make the case that narwhals aren’t only showing off with their tusks — the appendages have a variety of demonstrated uses that help the animals survive in the ocean.

The narwhal’s tusk was an inspiration for unicorn myths. It’s known that only males have them, with rare exception, and that a big tusk is something female narwhals look for in a mate. But the animals have been difficult to study.

“They’re extremely shy and elusive whales,” said Kristin Laidre, an applied animal ecology professor at the University of Washington who was not involved in the study. “They’re really hard to approach. They’re really skittish.” She added that narwhals tended to spend their time far from shore and diving deep into the water, and that doing research in the Arctic was logistically complex, making them a challenging species to observe in the wild.

With the help of local Inuit communities, the team of researchers identified a spot in the Canadian High Arctic to set up camp and fly drones. The calm waters of Creswell Bay in Nunavut, where narwhals had previously been observed spending their summers, were shallow and clear and — combined with the 24-hour daylight in August — allowed the researchers to film some of the best footage of narwhals ever captured.

As Dr. O’Corry-Crowe and team studied their recordings, they identified previously unobserved tusk behaviors. And one of those behaviors looked an awful lot like playing.

In more than one instance, narwhals chased arctic char but did not, strangely, try to catch and eat it. The whales even slowed down when necessary to keep the fish just off the tip of their tusks. When they did interact with the fish in these encounters, they used gentle taps or nudges — a stark difference more aggressive uses of their tusks when they were observed hunting fish. And in fact, the arctic char also didn’t seem to always be trying to escape the pursuing narwhals.

“They are not actually foraging on the fish, and we were hesitant to use the word ‘play,’ but that is really what it looked like,” said Cortney Watt, a researcher with Fisheries and Oceans Canada, and an author of the study.

She added that it was also possible the older narwhals were using such behavior to teach younger ones how to pursue prey.

The footage also captured the whales doing some deft spearfishing. While narwhals had been seen before using their tusks to stun fish before eating them, this is the first published study documenting that behavior. The narwhals stabbed and slashed fish with both the tip and the shaft of their tusks, disabling and possibly killing the fish before consuming their prey.

While spearfishing, the narwhals were also interrupted by glaucous gulls, which kept diving into the water to snatch the fish. Though sea gulls are known to track and scavenge off the hunts of other sea mammals, this was the first recorded interaction of this behavior with narwhals, specifically.

Dr. Laidre said that it was best not to jump to too many conclusions about narwhal behavior observed in a single study. The researchers agree, and that is why they didn’t want to label the narwhals’ interactions with arctic char as play explicitly. Dr. O’Corry-Crowe added that many of the behaviors his team observed “raise more questions than they answer, but that’s what’s so exciting.”

“What we really need to do is go back and do some more work,” he said. “And I can’t wait to do that.”

A SpaceX Dragon spacecraft arrived at the International Space Station at 1:35 a.m. Eastern time, paving the way for Suni Williams and Butch Wilmore — two NASA astronauts who have remained in space for months longer than planned — to finally return home.

The Crew-10 mission, an international team of four astronauts from the U.S., Japan and Russia, joined Ms. Williams and Mr. Wilmore aboard the outpost in the early hours of Sunday. The crews will transfer duties before Ms. Williams and Mr. Wilmore return to Earth, along with two colleagues.

It has been a long journey for the pair, who initially arrived at the International Space Station last June on what was meant to be a brief, dayslong test flight of a new Boeing Starliner spacecraft. Instead, after malfunctions in the capsule, NASA scientists opted to leave the astronauts at the space station and bring back the Starliner empty.

Ms. Williams and Mr. Wilmore have lived on the space station for nine months, awaiting new crew members to relieve them of their duties so that operations can run smoothly. The capsule’s trip was due to launch in February but was delayed until this month.

Nine months is not an unusually long stay in space — many astronauts on the space station live there for months, and some have even lived there for more than a year. Ms. Williams and Mr. Wilmore have used the time to conduct experiments, many exploring what the absence of gravity does to a body.

The pair’s unexpectedly long stay in orbit has intrigued space nerds, hobbyists and members of the public alike, fascinated by their fate. Ms. Williams and Mr. Wilmore have embraced their circumstances, broadcasting regularly from the station and speaking fondly about their layover in space.

“It makes you really want to enjoy every bit of your time that you have up here,” Ms. Williams told “The Daily” last week.

After the crews conduct handover duties, the pair will begin their journey back to Earth, possibly as early as Wednesday morning.

Greenpeace is among the most well-known environmental organizations in the world, the result of more than 50 years of headline-grabbing protest tactics.

Its activists have confronted whaling ships on the high seas. They’ve hung banners from the Eiffel Tower. They’ve occupied oil rigs. A (fictional) activist even sailed with Greenpeace in an episode of “Seinfeld,” in hopes of capturing Elaine’s heart.

Now, Greenpeace’s very existence is under threat: A lawsuit seeks at least $300 million in damages. Greenpeace has said such a loss in court could force it to shut down its American offices. In the coming days, a jury is expected to render its verdict.

The lawsuit is over Greenpeace’s role in protests a decade ago against a pipeline near the Standing Rock Sioux Reservation in North Dakota. The pipeline’s owner, Energy Transfer, says Greenpeace enabled illegal attacks on the project and led a “vast, malicious publicity campaign” that cost the company money.

Greenpeace says that it played only a minor, peaceful role in the Indigenous-led protest, and that the lawsuit’s real aim is to limit free speech not just at the organization, but also across America, by raising the specter of expensive court fights.

The suit comes at a time of immense challenges for the entire environmental movement. Climate change is making storms, floods and wildfires more frequent and more dangerous. The Trump administration has commenced a historic effort to overturn decades of environmental protections. Many of the movement’s most significant achievements over the past half-century are at risk.

And in recent years the potential costs of protest have already risen.

The International Center for Not-for-Profit Law has tracked a wave of bills proposed since 2017 that toughen penalties against protesters. Many became law in the wake of the demonstrations against the pipeline at the center of the Greenpeace case (the Dakota Access Pipeline) and also the Black Lives Matter movement, which rose to prominence after the murder of George Floyd in 2020 by a police officer in Minnesota. More recently, the Trump administration has moved to deport international students who protested the war in Gaza.

Sushma Raman, interim executive director of Greenpeace USA, has called the trial in North Dakota “a critical test of the future of the First Amendment.”

Energy Transfer, one of the biggest pipeline companies in the country, has said that the lawsuit is over illegal conduct, not free speech. “It is about them not following the law,” the company said in a statement.

Founded in Vancouver in 1971, Greenpeace was hugely successful early on at what is now called “branding,” with its catchy name and daredevil stunts. But it has also faced major challenges: infighting, missteps, legal battles and questions about how to widen its base and remain relevant as it became an institution.

The larger environmental movement has grown, but also has struggled to gain attention in an increasingly fractured media landscape and as it has pivoted to the issue of climate change, which can be less tangible than previous targets of activism, like say opposing logging or oil-drilling in specific places.

“What they made their name on was the media spectacle, especially the ability to conduct a high-profile action that requires incredible tactical organization,” said Frank Zelko, a history professor at the University of Hawaii at Mānoa and the author of “Make It a Green Peace! The Rise of Countercultural Environmentalism.” That became “less efficacious” over time, he said, as competition for eyeballs grew and spectacular images, whether real or not, abound.

Greenpeace was founded as an offshoot of the Sierra Club based on the principles of ecology and anti-militarism. But pulling off daring stunts in pursuit of those principles, while also operating as a worldwide professional network, has always been a delicate balancing act.

After friction and fights for control of the organization in the late 1970s, Greenpeace International was established in the Netherlands as the head office, coordinating the activities of independent Greenpeace offices around the world, including Greenpeace USA.

The activities of its American branch are at the center of the lawsuit. Greenpeace International says its role was limited to signing one open letter. Greenpeace International has also countersued Energy Transfer in the Netherlands, seeking to recoup its legal costs under European laws that essentially allow it to challenge the Energy Transfer lawsuit as a form of harassment.

In Greenpeace’s Washington office, the Energy Transfer case has contributed to turbulence in the group’s highest levels.

In early 2023, the organization celebrated the appointment of Ebony Twilley Martin as sole executive director, calling Ms. Twilley Martin the first Black woman to be the sole director of a legacy U.S. environmental nonprofit. But she left that role just 16 months later, a development that two people familiar with the matter said was in part over disagreements about whether to agree to a settlement with Energy Transfer.

Born in ’60s upheaval

Greenpeace was born out of a moment of fear and upheaval, amid the Vietnam War, the nuclear arms race, acid rain and smog blanketing cities. Rex Weyler, 77, an early member, chronicled the history in his 2004 book “Greenpeace: How a Group of Ecologists, Journalists and Visionaries Changed the World.”

In Vancouver, Mr. Weyler met Bob Hunter, a columnist for The Vancouver Sun, and Dorothy and Irving Stowe, older Quakers who had left the United States in protest over war taxes and weapons testing. They were meeting like-minded people who saw a need for an ecology movement that would employ nonviolent direct action, following the examples of Mohandas K. Gandhi in India and the civil rights movement in the United States.

They would soon become an offshoot of a more traditional environmental group, the Sierra Club, after a disagreement over protest tactics.

Their first campaign was a mission to block U.S. nuclear weapons tests on Amchitka, a volcanic island in Alaska. An idea this group had floated within the Sierra Club — to sail a boat to stop the bomb — had been reported in The Vancouver Sun, though the head office of Sierra Club in San Francisco had not approved that plan.

“The Sierra Club was not amused when they saw this story, because they said, ‘You know, a lot of our members are just tree-huggers, and they don’t care about nuclear disarmament,’” said Robert Stowe, son of Dorothy and Irving and a behavior neurologist. “Had the Sierra Club agreed to do this, Greenpeace could probably never have been founded.”

The name Greenpeace came up during a planning meeting, when Irving Stowe said “peace” at the end of the gathering and another activist, Bill Darnell, replied offhandedly, “Make it a green peace.”

“Greenpeace” was emblazoned on the fishing boat they used. Irving Stowe organized a concert by Joni Mitchell, James Taylor and Phil Ochs to raise money for the trip.

The boat set sail in September 1971. The Coast Guard intercepted it, and the vessel never reached Amchitka. But the stunt garnered considerable public attention, a core part of the group’s strategy in the years since.

‘Save the whales’ era

Greenpeace’s next campaign is perhaps its most well known: saving the whales.

The idea came from Paul Spong, who had studied orca whales and argued that the highly intelligent creatures were being hunted to extinction. That led to a copiously documented, dramatic sailing expedition to confront Soviet whaling ships.

A worldwide moratorium on commercial whaling has been in place since 1986. Greenpeace and other groups who worked on the issue have claimed it as a major victory.

The group also tried to stop seal hunting in northern Canada, a controversial move that alienated a large number of residents, including in Indigenous communities. Greenpeace Canada apologized to the Inuit people for the impacts of the campaign in 2014, and the organization said it did not oppose small-scale subsistence hunting.

The ship Rainbow Warrior, a crucial vessel in the anti-whaling campaign, was added to the fleet in 1978. That ship was protesting French nuclear testing in the Pacific in 1985 when it was bombed by agents for the French spy agency D.G.S.E., killing Fernando Pereira, a photographer, and igniting international outrage.

France later apologized and was ordered to pay $8 million in damages to Greenpeace, and reached a separate settlement with Mr. Pereira’s family.

A new Rainbow Warrior is now one of three Greenpeace vessels in operation. It is sailing this month in the Marshall Islands to “elevate calls for nuclear and climate justice,” the group said, and to support research on the effects of past nuclear weapons testing.

Growing pains

By the 1990s, Greenpeace’s attention-grabbing environmentalism was capturing the imagination of a new generation of people like Valentina Stackl, 39, who learned of its exploits as a girl in Europe. She worked with Greenpeace USA from 2019 to 2023.

“The idea of Greenpeace ships, and save the whales and hanging off a bridge or something like that was truly magical,” she said. “And on the best days Greenpeace really was like that. Of course, there’s also the slog of the day-to-day that is less sparkly.”

One constant concern was fund-raising: Greenpeace USA is largely funded by individual donations, which can fluctuate. Tax filings show its revenue has been stable in recent years.

The group’s priorities shifted to climate and how to incorporate what is known as “environmental justice,” the fact that pollution and other environmental hazards often disproportionally affect poor and minority areas. The historically mostly white and male-dominated organization had to grapple with how to increasingly collaborate with a diverse range of other groups. And it had to reckon with historical tensions with Indigenous communities over its whaling and sealing campaigns, as well as other missteps.

One of those mistakes occurred in Peru in 2014, when there was an uproar over a Greenpeace action that damaged the Nazca lines, ancient man-made patterns etched in the desert. Activists from Greenpeace Germany entered the restricted area to place a protest message about renewable energy. The Peruvian cultural minister called it an act of “stupidity” that had “co-opted part of the identity of our heritage.”

The organization apologized, and the episode prompted Greenpeace USA to adopt a formal policy on interactions with Indigenous communities, according to Rolf Skar, the group’s campaigns director. In short, Greenpeace would not get involved in struggles led by Indigenous people unless specifically asked to do so.

That policy has come up in this month’s trial in North Dakota. Greenpeace argued that it had offered support in the Dakota Access Pipeline protest only after it was asked to do so by Indigenous leaders, and did not seek any major role in the demonstrations.

On Monday in a courtroom in the small city of Mandan, N.D., jury members are expected to start hearing closing arguments, after which they will consider Greenpeace’s fate.