Federal officials are planning to expand the critical habitat for an endangered native seal to Johnston Island and the main Hawaiian Islands, in light of the marine mammal's decline in the Northwestern Hawaiian Islands.

The officials will be looking at potential critical habitat areas for the monk seals to give them added protection, said Lance Smith, a biologist with the protected resources division of the National Oceanic and Atmospheric Administration.

The government defines a critical habitat as an area that is designated as essential to the species' conservation.

The decision is expected to be published today in the Federal Register, according to environmental groups seeking the expanded designation.

Federal officials designated the Northwestern Hawaiian Islands from Kure atoll to Nihoa island as critical habitat for the monk seals in 1988.

Environmental groups petitioned the National Marine Fisheries Service in July after noticing that the monk seals seemed to be doing better in the main Hawaiian Islands.

“;We're elated,”; said Marti Townsend, an official with the group Kahea: The Hawaiian-Environmental Alliance.

Miyoko Sakashita, staff attorney for the Center for Biological Diversity, said the main Hawaiian Islands look like one of the last places where the monk seals are healthy and able to recover.

Smith said federal officials will be determining what areas are critical habitat for monk seals in the main Hawaiian Islands and assess the impact of designation, including its effect on the economy.

Federal officials would also measure the impact on national security if they proposed designating critical habitat in military areas, such as Bellows Beach near Waimanalo, Barking Sands on Kauai and Pearl Harbor.

Developers would have to meet standards intended to preserve critical habitats when using federal funds or applying for federal permits.

As endangered species, monk seals already enjoy some federal protection, such as being protected from being killed, injured or harassed.

The number of monk seals was estimated at 1,208 in 2006 in the Northwestern and main Hawaiian Islands.

Their number has been decreasing at an estimated rate of 4 percent a year in the Northwestern Hawaiian Islands but growing in the main Hawaiian Islands with an increase in sightings from 45 in 2000 to 83 in 2006, according to the National Marine Fisheries Service.