A North Atlantic right whale surfaces on Cape Cod Bay in Massachusetts. The protected species has been at the center of a longtime dispute between federal regulators and commercial fishing and shipping industries. Robert F. Bukaty/Associated Press

On a breezy spring day, scientists and conservationists methodically conducted experiments near 15 North Atlantic right whales that occasionally spouted and surfaced in a bay south of Boston.

The pod of adults and calves is about 4% of the worldwide population of a marine mammal that almost disappeared from the planet after many decades of commercial whaling. There now are only a few hundred of the behemoths, which can weigh 70 tons and subsist on small ocean organisms.

Although right whale numbers are dwindling, conservationists attribute their continued survival to the U.S. Endangered Species Act.

The landmark federal law — a half century old this year — has forced the fishing and commercial shipping industries to take important steps to help protect the critically endangered whales. And it spurred government agencies and scientists to undertake research.

David Wiley, research ecologist with the National Oceanic and Atmospheric Administration, was part of the crew that spent late March and early April testing the water off Cape Cod for the presence of a naturally occurring chemical that could help predict where right whales will congregate.

That knowledge, Wiley said, can help in forming new rules that safeguard the whales from threats such as entanglement in fishing gear and collisions with ships. While Wiley’s crew was working, a right whale was found entangled in Cape Cod Bay.

“They will go extinct in our lifetime if we don’t do something,” he said. “The goal of my research is to protect animals, right whales, humpback whales.”

Numerous whale species are protected under the Endangered Species Act, including the blue, fin and sperm whale. Some, including the North Atlantic right whale, have been listed since the act passed in 1973. The law also protects other marine mammals, including some seal species, and ocean dwellers such as sea turtles.

Few animals have brought more change to marine industries than the right whale, and conservationists say survival of the species, which numbers about 340 worldwide, is testament to the act’s importance.

“While they continue to decline at this very moment, I’m convinced that without the Endangered Species Act they wouldn’t be here,” said Regina Asmutis-Silvia, executive director of Massachusetts-based Whale & Dolphin Conservation USA.

But as federal regulators craft new protections for the whale and other declining marine animals, fishing and shipping industries that have been altered by decades of conservation laws are digging in for a new round of fighting for their own interests.

The U.S. lobster fishing industry, one of America’s most lucrative seafood sectors, supports the act, said Beth Casoni, executive director of the Massachusetts Lobstermen’s Association. But she said fishermen also need reasonable rules and some recent proposed restrictions on fishing go too far.

In recent years, disagreements over the proper way to apply the act have increasingly brought the industry into court. “We need to have realistic approaches to how environmental management is handled,” Casoni said. “It becomes extremely costly for the industry to fight the ongoing litigation that’s brought forth by the environmental groups.”

Maritime industries are subject to a host of restrictions aimed at protecting the rare whales. Rules cover how fast vessels can travel and where commercial fishermen can fish. There are slow zones, protected zones and limitations on types of fishing gear.

The act has permanently protected thousands of square miles of ocean habitat to give the animals sanctuary from disturbances by human activities. The act has prompted innovations, such as ropeless fishing, designed to protect whales from becoming entangled. Compliance with the act primarily drove the use of nets with escape hatches to spare turtles from shrimp fishing on the Gulf Coast.

Fisheries for lucrative seafood species, such as scallops and groundfish, also have made changes to conform with the act. The act has brought observers onto fishing boats to make sure fishermen follow rules and it has barred fishing in places where vulnerable species are located.

“I feel like it drives technological innovation, and it also protects a whole suite of other species by reducing risks for whatever the listed species is,” said Janet Coit, assistant administrator for fisheries with NOAA’s National Marine Fisheries Service, which regulates commercial fishing. “The law has stood the test of time.”

The law’s protections are set to expand in coming years. On the East Coast, NOAA is crafting new and broader fishing restrictions to reduce the likelihood whales will suffer injury or death from entanglements in gear. The agency also is considering enlarged speed restriction zones that will apply to many shippers.

On the West Coast, new protections are coming for endangered whales off California. The International Maritime Organization has adopted a U.S. proposal that takes effect this summer and would expand restrictions on vessel traffic to give endangered whales such as blues and fins more undisturbed sea.

Lobster fishers have vowed to fight new restrictions on fishing off the East Coast, which many say will put the industry out of business. Proposed restrictions necessitate new ropeless gear that isn’t widely available yet, said David Cousens, a lobsterman in South Thomaston, Maine.

“The technology’s not there. Common sense is what needs to prevail here, not pie in the sky dreaming,” Cousens said.

Vessels strikes and entanglements are two of the biggest threats whales face. But expansion of vessel traffic restrictions has also been met with resistance from shippers who fear compliance will be difficult, said Kathy Metcalf, president of the Chamber of Shipping of America.

“All we are trying to do is get some reasonable restrictions in place and still be able to serve the people who are waiting for their Nike sneakers and fuel oil or whatever and still serve a measure of protection to the animals,” Metcalf said.

Long a focus of conservationists, the plight of whales helped inspire the Endangered Species Act. Many species were devastated during the commercial whaling era, when they were hunted for meat and oil.

The gray whale, ranging from Mexico to Alaska in the Pacific, is often held up as one of the act’s greatest success stories since it was delisted in 1994 after populations rebounded. The U.S. government also has removed most populations of humpback whales from the list following recovery.

“The Endangered Species Act has a legal impact. A tangible result,” said Charles “Stormy” Mayo, senior scientist at the Center for Coastal Studies in Provincetown, Massachusetts, which works to preserve marine animals. “The Endangered Species Act has lifted our sensitivity to rare species.”

Others, like the North Atlantic right whale, have been slower to recover. The whale’s population is falling in part because of climate-related warming of the ocean, which scientists say is pushing the animals outside protected zones and into harm’s way in search of food. They’ve lost about 30% of their population since 2010.

The swift decline shows the act can’t save an animal if it’s not applied aggressively, said Michael Moore, director of the Woods Hole Oceanographic Institution Marine Mammal Center in Massachusetts. “That level of collapse can hardly be seen as a success,” Moore said.

If the whale is to survive, the law will need to play a critical role, said Gib Brogan, fisheries campaign manager for the conservation group Oceana.

“The Endangered Species Act is a big hammer … that has forced action, necessary action, to make sure that the needs of these species are taken care of both in fisheries management and other activities where otherwise they would be ignored,” Brogan said.