US President Donald Trump has signed an executive order allowing commercial fishing in the Pacific Islands Heritage Marine National Monument (PIH), one of the world’s largest protected ocean areas. The move lifts a ban in place since 2009 and allows US-flagged fishing vessels to operate within 50 to 200 nautical miles of the monument’s boundaries.

Covering nearly 500,000 square miles of ocean — about twice the size of Texas — PIH is home to coral reefs, endangered sea turtles, whales, sharks, manta rays, and many other marine species. The area was first protected by former president George W. Bush and expanded by former president Barack Obama to preserve biodiversity and protect important cultural sites.

The Trump administration said the fishing ban hurt US fishers by pushing them farther away and forcing them to compete with foreign fleets. Officials claimed opening the area would help the American fishing industry.

However, environmentalists and scientists are alarmed. They warn that allowing industrial fishing could damage the fragile marine ecosystem and undo years of conservation work. Experts say PIH is a key area for migratory species like tuna to recover and breed, and opening it to fishing could threaten their populations.

There are also concerns about the labor conditions on many fishing vessels, which are often crewed by low-paid foreign workers facing tough and unsafe working conditions.

Although the government says existing environmental laws will still protect the area, critics argue these don’t offer the same level of protection as a full fishing ban — and some of those laws may be weakened or rolled back.

The monument is not only important for marine life but also holds deep cultural and spiritual meaning for Indigenous Pacific Islander communities. Many fear the decision ignores both environmental and cultural values.

Trump also ordered a review of other marine monuments, raising the possibility that more protected ocean areas could be opened to commercial fishing in the future.

As fishing fleets prepare to enter previously protected waters, environmental groups and local communities are bracing for the possible damage to one of the planet’s last untouched ocean habitats.