Question: The North Pacific albatross are the most tropical of the albatrosses with two species one of which primarily lives in the Northwestern Hawaiian Islands with an estimated population of how many?

Context paragraphs:
Phoebetria: The sooty albatrosses are small albatrosses from the genus Phoebetria.  There are two species, the sooty albatross, "Phoebetria fusca", and the light-mantled albatross, "Phoebetria palpebrata".  The sooties have long been considered distinct from the rest of the other albatrosses, and have retained their generic status through the many revisions of the family over the last 150 years.  They have traditionally been thought of as primitive, sharing some morphological features with the other petrel families.  However, molecular work examining the mitochondrial DNA has shown that the taxon is related to the mollymawks, and that the two taxa are distinct from the great albatrosses and the North Pacific albatrosses.

Great albatross: The great albatrosses are seabirds in the genus Diomedea in the albatross family.  The genus "Diomedea" formerly included all albatrosses except the sooty albatrosses, but in 1996 the genus was split, with the mollymawks and the North Pacific albatrosses both being elevated to separate genera.  The great albatrosses themselves form two species complexes, the wandering and Amsterdam albatrosses, and the royal albatrosses.  The splitting of the great albatrosses into six or seven species has been accepted by most, though not all authorities.

Laysan albatross: The Laysan albatross ("Phoebastria immutabilis") is a large seabird that ranges across the North Pacific.  The Northwestern Hawaiian Islands are home to 99.7% of the population.  This small (for its family) gull-like albatross is the second most common seabird in the Hawaiian Islands, with an estimated population of 2.5 million birds, and is currently expanding (or possibly re-expanding) its range to new islands.  The Laysan albatross was first described as "Diomedea immutabilis" by Lionel Walter Rothschild, in 1893, on the basis of a specimen from Laysan Island.

List of fish of Hawaii: The fish species of Hawaii inhabit the Hawaiian archipelago in the central North Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of Australia.  The islands are part of the State of Hawaii, United States.  The state encompasses nearly the entire volcanic Hawaiian Island chain, which comprises hundreds of islands spread over 1500 mi .  At the southeastern end of the archipelago, the eight "main islands" are (from the northwest to southeast) Niʻ ihau, Kauaʻ i, Oʻ ahu, Molokaʻ i, Lānaʻ i, Kahoʻ olawe, Maui, and Hawaiʻ i.  The Northwestern Hawaiian Islands include many atolls, and reefs. Due to Hawaii's isolation 30% of the fish are endemic (unique to the island chain).

Black-footed albatross: The black-footed albatross ("Phoebastria nigripes") is a large seabird of the albatross family Diomedeidae from the North Pacific.  All but 2.5% of the population is found among the Northwestern Hawaiian Islands.  It is one of three species of albatross that range in the northern hemisphere, nesting on isolated tropical islands. Unlike many albatrosses, it is dark plumaged.

Short-tailed albatross: The short-tailed albatross or Steller's albatross ("Phoebastria albatrus") is a large rare seabird from the North Pacific.  Although related to the other North Pacific albatrosses, it also exhibits behavioural and morphological links to the albatrosses of the Southern Ocean.  It was described by the German naturalist Peter Simon Pallas from skins collected by the Georg Wilhelm Steller (after whom its other common name is derived).  Once common, it was brought to the edge of extinction by the trade in feathers, but with protection has recently made a recovery.

North Pacific albatross: The North Pacific albatrosses are large seabirds from the genus "Phoebastria" in the albatross family.  They are the most tropical of the albatrosses, with two species (the Laysan and black-footed albatrosses) nesting in the Northwestern Hawaiian Islands, one on sub-tropical islands south of Japan (the short-tailed albatross), and one nesting on the equator (the waved albatross).

Wandering albatross: The wandering albatross, snowy albatross, white-winged albatross or goonie ("Diomedea exulans") is a large seabird from the family Diomedeidae, which has a circumpolar range in the Southern Ocean.  It was the first species of albatross to be described, and was long considered the same species as the Tristan albatross and the Antipodean albatross.  A few authors still consider them all subspecies of the same species.  The SACC has a proposal on the table to split this species, and BirdLife International has already split it.  Together with the Amsterdam albatross, it forms the wandering albatross species complex.  The wandering albatross is one of the two largest members of the genus "Diomedea" (the great albatrosses), being similar in size to the southern royal albatross.  It is one of the largest birds in the world, and one of the best known and studied species of bird in the world.  This is also one of the most far ranging birds.  Some individual wandering albatrosses are known to circumnavigate the Southern Ocean three times (covering more than 120,000 km or 75,000 miles) in one year.

Maro Reef: Maro Reef (Hawaiian: Nalukākala - "surf that arrives in combers") is a largely submerged coral atoll located in the Northwestern Hawaiian Islands.  It was discovered in 1820 by Captain Joseph Allen of the ship "Maro", after whose ship the reef was named.  With a total area of 747 sqmi , it is the largest coral reef in the Northwestern Hawaiian Islands.  It contains 37 species of stony coral.  Unlike most atolls, the coral extends out from the center like spokes on a wheel.  Located about 850 mi northwest of Honolulu, Hawaii, Maro Reef contains about 1 acre of dry land which itself can be submerged depending on the tides.  Some scientists believe that it "may be on the verge of drowning" because the reefs are detached and are vulnerable to strong storm waves.

Necker Island (Hawaii): Necker Island (Hawaiian: Mokumanamana) is a small island in the Northwestern Hawaiian Islands.  It is located at in the Pacific Ocean, 155 mi northwest of Nihoa and 8 mi north of the Tropic of Cancer.  It contains important prehistoric archaeological sites of the Hawaiian culture and is part of the Hawaiian Islands National Wildlife Refuge within the Northwestern Hawaiian Islands National Monument.

Supporting paragraphs: North Pacific albatross Laysan albatross
Answer: 2.5 million