Thursday marks 50 years sincethe federal Endangered Species Act was signed into law by President Richard Nixon.

The landmark conservation legislation has been celebrated for helping restore populations of threatened wildlife, and for inspiring state laws that protect even more species. But even as advocates in Massachusetts tout successes of the law, they say more protections are necessary to protect critically endangered species as the threats they face evolve.

"It's had an enormous impact," said Jesse Leddick, the incoming assistant director of the Natural Heritage and Endangered Species Program at Massachusetts' Division of Fisheries and Wildlife.

The federal law provides legal protections for species of plants or animals that meet the criteria for one of two designations. If a species is considered in danger of extinction, it's designated as "endangered." Species that are likely to become endangered in the foreseeable future are considered "threatened."

Endangered and threatened species face many of the same stressors they faced when the Endangered Species Act first passed, Leddick said, but some threats are new or are a bigger concern than they once were.

"Climate change is a big one. Habitat loss, with urbanization and development, is at a scale and pace that I don't think we saw 50 years ago," he said. "So the challenges are similar but growing. And so I think the need for the ESA and for similar pieces of legislation are even more important."

"Climate change is a big one [threat]. Habitat loss, with urbanization and development, is at a scale and pace that I don't think we saw 50 years ago."
Jesse Leddick

The Endangered Species Act is credited with helping restore the population of species like the bald eagle. For Leddick, another key example of the law's success is the peregrine falcon.

"Now we actually have more peregrine falcons in Massachusetts than we had before the ESA was passed," he said. "I think we have something like close to 50 breeding pairs here in the state when I think previously we had only about 25."

It's also played an important role in protecting less charismatic species, Leddick added.

"Plants are a good example," he said. "Plants are sometimes rare and endangered for multiple different reasons, and the Endangered Species Act gives protection to those in a way that didn't exist prior to that. So that was, I would say, a huge step forward."

The federal law also helped inspire more local conservation legislation, like Massachusetts' own Endangered Species Act, which became law in 1990. The state law protects 432 species, including many that are not on the federal list.

The North Atlantic right whale is among the species on the federally endangered list. Today, the total population of right whales is estimated to be just over 350.

"The job is not done yet for the species," said Amy Knowlton, a senior scientist at the New England Aquarium. "This population is close to extinction."

The Endangered Species Act did provide protections by designating critical habitat areas where right whales forage or bring up their young.

"It recognizes where habitats are critical for these species to survive and then manages activities — federal activities, primarily — that may be happening in those habitats," Knowlton said.

But some of the key threats to right whales — including ship strikes and entanglements in fishing gear — often happen outside those designated areas, Knowlton said.

"What we're learning is that it's happening throughout their range," she said. "And therefore we have to think more broadly than I think what the government has done thus far, and start to think more broadly about changing how these industries operate."

Leddick said it's important to defend the Endangered Species Act from attacks from industry and other interests who would like to see the federal legislation watered down.

"I think that going forward, we need to both support federal and State Endangered Species Act, but also the related environmental legislation," he said. "And in some ways, I would say move beyond single-species thinking and thinking more about biodiversity collectively."

To that point, Leddick pointed to an executive order signed by Gov. Maura Healey in September directing the state to develop biodiversity goals.

"I see imperiled species as canaries in the coal mine," Leddick said. "They're the species that really show us what's happening in our environment and whether things are good or not good, and whether action is needed. So I think it's even more important than it was then, today."