"This is a landmark conservation event," Joshua Reichert of the Pew Charitable Trusts told the Washington Post.
"It is important to restrict activities that have the potential to damage the marine environment, of which fishing is a big one," said Reichert, who heads the nonprofit's environmental program.
The Antiquities Act of 1906 gives the U.S. President the executive authority to set aside objects of historic or scientific interest as national monuments.
The Ocean Conservancy, which along with other conservation groups says it was caught off guard by Bush's announcement, says monument status will help safeguard one of the world's last pristine ocean ecosystems.
"A national monument designation is the strongest level of enduring protection we can provide," said Ellen Athas, director of ecosystems protection for the Washington, D.C.-based group.
The group's president, Roger Rufe, described the NWHI as a "national treasure" on par with Yellowstone and Grand Canyon National Parks.
"The marine ecosystem around the Northwestern Hawaiian Islands is one of the most biologically diverse areas in U.S. oceans," he added.
Although the Bush Administration has been widely criticized for its record on environmental protection, Rufe praises its latest decision.
"Teddy Roosevelt is largely considered the father of our national park system," he said. "President Bush may be securing a similar legacy in our oceans."
Reports suggest that under the new status, taking fish, wildlife, corals, and minerals from the region will be completely prohibited.
Native Hawaiians will have access to the area for traditional activities. Visitors wishing to snorkel, dive, or take photographs around the islands will have to first obtain a permit.
Conservationists say the threats to marine life in the NWHI include small-scale commercial fishing operations that target lobsters and seabed-dwelling fish.
Damage caused by discarded fishing gear and other debris has been highlighted as a concern. At least 155 Hawaiian monk seals have reportedly become entangled in such debris since 1982.
The Ocean Conservancy says tourism in the islands brings additional noise and water pollution, including effluent discharges from cruise ships, and the threat of introductions of non-native species.
The NWHI support many endemic species found nowhere else, including four birds, three land snails, 12 plants, and more than 60 invertebrates.
"Ocean islands in general tend to have high levels of [unique species], due largely to their isolated nature, and the Hawaiian archipelago is the most isolated in the world," Jason Baker told National Geographic News earlier this month.
Baker is a scientist at the Pacific Islands Fisheries Science Center in Honolulu, Hawaii, who has been researching the NWHI.
"These little islands are important nurseries for monk seals, sea turtles, and millions of seabirds," he added.
A recent study led by Baker suggests the islands, many of which are low lying, are at risk from rising sea levels caused by global warming.
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