The Northeast Canyons and Seamounts Marine National Monument spans nearly 5,000 square miles -- larger than Yellowstone National Park.

Long a focus of scientific interest, the monument lies about 130 miles southeast of Cape Cod, Massachusetts, and was established in 2016 by former Democratic president Barack Obama, who warned it was threatened by overfishing and climate change.

In a familiar political yo-yo, Republican Trump reopened the monument to commercial fishing during his first term, only for the decision to be reversed by Democratic successor Joe Biden. Biden's administration cited the monument as part of its pledge to conserve 30 percent of US land and waters by 2030.

Explaining the latest reversal, Trump's proclamation said the plants and animals in question were already protected under existing laws, making a ban on commercial fishing unnecessary.

The move, expected since last year, was welcomed by the New England Fishermen's Stewardship Association (NEFSA).

"For decades, overregulation has stopped fishermen from making a living and putting wild, heart-healthy, American-caught products on store shelves. NEFSA is pleased that the Trump administration is committed to making America's natural resources available to all Americans," said NEFSA CEO Jerry Leeman in a statement last May.

Conservation groups, however, pushed back.

During an aerial survey last August, the New England Aquarium documented more than 1,000 marine animals in the area, including an endangered fin whale and calf, an endangered sperm whale, pilot whales, and a wide array of other whales, dolphins and rays.

"This Monument supports amazing species from the seafloor to the sea surface, and we see evidence of that during every aerial survey," said Jessica Redfern, of the aquarium's Anderson Cabot Center for Ocean Life.

"Removing protections for Northeast Canyons and Seamounts Marine National Monument puts these species at risk."