In July, People for the Ethical Treatment of Animals (PETA) sent an impassioned letter to Axel Dumas, the chief executive of Hermès. It asked him to stop using crocodile skins for the handbags that bear Jane Birkin’s name, the actress and singer who had just died, and to begin “implementing a compassionate new policy against the use of all exotic skins so that no more animals will be killed in her name.” The letter echoed a statement Ms. Birkin herself had made, in 2015, when she asked the brand to remove her name from the crocodile-skin iteration of the bag for similar reasons.

Hermès, in its reply, wrote that “animal welfare policies remain a top priority,” and that “a requirement for absolute quality” applies to the materials that go into its products.

For many years, luxury watch straps made from such exotic skins — especially alligator, since the average alligator tends to have flatter, smaller scales than a crocodile, and therefore, is better suited for use in small leather goods — were the ultimate finishing touch to a high-end timepiece. Today, however, some brands say many of their customers don’t want straps made from exotic skins any more.

“We’ve actually begun to see quite a large decline in the number of customers who would request an alligator strap,” said Nicholas Bowman-Scargill, managing director of the British brand Fears Watches.

Some five years ago, he said, all the brand’s mechanical watches came on alligator straps. It stopped carrying straps made from that hide and, except for one remaining piece, no longer sells alligator straps at all. Now, nearly all of its watches come on leather straps — while some have metal ones — and, Mr. Bowman-Scargill said, of his customers, “the number who are requesting animal-free has gone up dramatically.” So on Sept. 29, Fears plans to begin introducing straps made of Alcantara, a synthetic material that resembles suede.

Beyond assuaging customers’ environmental and ethical considerations, making this kind of shift can actually reduce a brand’s paperwork burdens, too. After all, using exotic skins in watch straps involves a labyrinthine process of documentation.

Trade in crocodile, alligator, lizard and python, whether live or as hides, is regulated by CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora. An international agreement that became effective in 1975, CITES tracks products from animals that risk becoming extinct, tracing their origins and movements among countries. Each country’s corresponding regulatory body — which, in the United States is the U.S. Fish & Wildlife Service — is charged with ensuring that CITES rules are followed by manufacturers and retailers using such animal products.

New watch straps often involve several rounds of import and export: an alligator strap purchased by a collector in the United States, for example, could easily start as a skin in Louisiana, the site of many of the world’s alligator farms; be sent to France for tanning and manufacturing, then be shipped back to the U.S. for sale. Each portion of that trip would require CITES documentation.

“It’s like a passport,” said Yann Perrin, chief executive of Atelier du Bracelet Parisien, better known as ABP Concept, a company that makes watch straps and other accessories.

He was speaking at his office in the First Arrondissement of Paris, surrounded by alligator skins in finishes like matte black and glossy bright green. CITES forms, filed online, must accompany shipments of his brand’s straps — about 60 percent of which, he noted, are alligator and about half of which are custom made — to clients around the world. At ABP, an alligator strap starts at 155 euros ($166); a custom strap for a 38-millimeter watch retails for about €300.

According to the convention’s rules, individuals who buy a watch with an exotic skin strap abroad and want to bring it home need CITES documentation, as the regulations apply to personal purchases as well as commercial shipping. But many shoppers are not aware of the requirement, and customs officials often don’t check on individual purchases.

The secondary watch market, including auction houses and vintage watch dealers, is also subject to CITES regulations. Resellers don’t typically have access to the original CITES documentation for the straps on the timepieces they sell, which is why Phillips, Sotheby’s and other auction houses remove the watch straps before shipping.

“We have, like, this fear of God in making certain to take off the crocodile straps before we ship any timepiece outside of any country, whether the watch is in Hong Kong, Japan, Switzerland — or from New York to any country outside of the United States,” said Paul Boutros, Phillips’s deputy chairman and head of watches in the Americas.

“There are fines involved and we don’t want to violate any restrictions,” he added.

Processing CITES documentation for shipments involves fees, which Mr. Bowman-Scargill of Fears Watches said can substantially add to the price of a watch strap, making it prohibitively expensive. But, “it’s not just the actual cost of the documentation,” he said. “It’s also the cost of a member of my team having to do all the process — chasing it up, applying for it. It can be hours.”

Still, Mr. Bowman-Scargill said he understands the importance of CITES. “It’s what stops people just going out and killing wild animals and selling their skins without documentation,” he said. “I’m not at all someone who is anti-CITES, but it’s a very, very difficult, laborious process.”

Some strap makers see CITES documentation as a normal part of doing business. “I don’t see it as something negative or the worst part of the job,” said Aaron Pimentel, founder of the Montreal-based company Aaron Bespoke, which makes straps and items like belts and wallets. “I just see it as part of the deal and I’m happy to do it.”

At his company, CITES-related paperwork takes about six hours per shipment, he said, but it helps that his straps are often sent in bulk (with some 30 to 60 straps per shipment), to countries such as the United States, which generates about 40 percent of the business’s sales.

Quite a few luxury brands have discontinued selling exotics, perhaps more with consumer perception than CITES regulations in mind. Chanel and Burberry no longer sell products made of reptile skins, for example, and some department stores, like Nordstrom and Selfridges, have stopped carrying products made with reptile skins.

“The new millennial customer, is very attuned to the environment, to ethical treatment,” said Robert Burke, the founder of a namesake retail, fashion and hospitality consultancy in New York City. “They’re hypersensitive to it.”

Wearing a watch without a reptile strap, he added, “is a big personal statement that you’re conscious enough to make the effort to wear something that is nonleather or an alternative. I think there are certain bragging rights that go along with that.”

“Ten years ago, everyone was thinking luxury has to be crocodile,” said Pierre-Louis Follet, who runs the French strap specialist Jean Rousseau in the United States, at the brand’s atelier in Midtown Manhattan.

Today, the brand’s array of options includes straps in materials like sturgeon skin, cactus, cork and mushroom.

“Today luxury is being smart, so it’s being different,” Mr. Follet said.