Three-dimensional computer models developed by a group of Hawai'i scientists predict that some of the Northwestern Hawaiian Islands could lose as much as 65 percent of their area by the end of the century if sea levels continue to rise.

Most at risk from the habitat loss would be the Hawaiian monk seal, the Laysan finch and the Hawaiian green sea turtle, according to research findings published in the international conservation journal Endangered Species Research.

The study is the first to detail the topography of the islands and evaluate the effect of rising sea levels on native species.

"These little islands are important nurseries for monk seals, sea turtles and millions of seabirds. Yet much of this lively activity occurs just a few meters above sea level," said Jason Baker of the National Marine Fisheries Service's Pacific Islands Fisheries Science Center in Honolulu, one of the authors of the research.

The Northwestern Hawaiian Islands — the most remote archipelago in the world — are soon expected to become a national marine sanctuary, and much of the wildlife conservation efforts there have been focused on their rich abundance of marine life — not on land-based animals, Baker said. Native to the islands are four land bird species, three terrestrial snail species, 12 plant species and more than 60 species of arthropods, which include insects, spiders and crustaceans, that spend their entire lives on land.

Scientists say the world's sea level rose 6 inches during the past century and is anticipated to increase further due to warmer ocean waters and melting glaciers and ice caps.

For their study, Baker and fellow National Oceanic and Atmospheric Administration researcher Charles Littnan and David Johnston of the Joint Institute for Marine and Atmospheric Research last year visited French Frigate Shoals, which has nine islets, and Pearl and Hermes Reef, which has seven islets and several sand spits that come and go. Virtually all the land at both locations is less than 6 1/2 feet above sea level. The trio also collected data at Lisianski, a relatively large, low-lying island.

Using traditional surveying methods and Global Positioning System receivers, they calculated land elevations.

Their computer maps projected that Lisianski would be the least affected by a predicted 19-inch rise in sea level by 2100, losing only 5 percent of its area. In contrast, the islets at French Frigate Shoals and Pearl and Hermes were projected to lose up to 65 percent of their area.

The study said Lisianski Island may provide a longer-term refuge for animals, since even after a 6 1/2-foot rise in sea level, more than 80 percent of its land area would be expected to remain.

"However, the island would rapidly become submerged as the sea level rises to almost 8 feet," the report said. "The land areas we measured at French Frigate Shoals and Pearl and Hermes Reef would disappear with a (6 1/2-foot) rise."

French Frigate Shoals is a popular landing site for sea turtles and monk seals, one of the rarest marine mammals in the world with only about 1,300 individuals. Baker said shrinking habitat due to rising sea levels might increase overcrowding and competition for other sites, possibly contributing to a further decline in seal numbers.

The study also said land loss could "greatly increase" the extinction risk for the Laysan finch, an endangered Hawaiian honeycreeper. The birds were established at Pearl and Hermes Reef in the 1960s as a backup to the primary population on Laysan.

Baker said starting up another population of finches at a location less vulnerable to sea level rise, such as Lisianski Island, may be warranted. Other higher-elevation islands such as Laysan, Necker and Nihoa also may provide space for displaced animals.

The study mentions beach nourishment, in which sand is strategically deposited onto beaches, as another possible mitigation measure to counter the effects of rising sea levels at the Northwestern Hawaiian Islands.

Baker said more sophisticated research is needed to study more of the islands and potential sea level impacts. The good news is that the danger is not imminent.

"It's not something that's going to happen tomorrow," he said. "But it hasn't had any real attention and it's something we should be thinking about for long-term planning."

Reach Christie Wilson at cwilson@honoluluadvertiser.com.