President Donald Trump signed an executive order Thursday that seeks to open up 400,000 square miles of ocean southwest of Hawaii to commercial fishing, a move local groups see as "short-sighted" and harmful for a vast ecologically and culturally significant stretch of the Pacific.

Mr. Trump issued an executive order opening up the Pacific Islands Heritage Marine National Monument, which lies some 750 miles west of Hawaii. President George W. Bush established the monument in 2009 and President Barack Obama expanded it in 2014 to its current area of nearly 500,000 square miles.

On April 17 the White House shared a proclamation opening the waters around the Pacific Islands Heritage Marine National Monument open to commercial fishing by U.S. flagged vessels.