The warm, shallow waters surrounding the main Hawaiian Islands constitute one of the world's most important humpback whale habitats and the only place in the U.S. where humpbacks reproduce. Scientists estimate that two-thirds of the entire North Pacific humpback whale population (approximately 2000-3000 whales) migrate to Hawaiian waters to engage in breeding, calving and nursing activities. The continued protection of humpback whales and their habitats is crucial to the long-term recovery of this endangered species.

Congress, in consultation with the State of Hawaii, recognized the importance of Hawaii's nearshore waters to humpbacks by designating the Hawaiian Islands Humpback Whale National Marine Sanctuary (Sanctuary) on November 4, 1992 (Hawaiian Islands National Marine Sanctuary Act or Act). The Act identifies the following purposes for the Sanctuary:

The designated boundary includes the area from the high water mark to the 100-fathom (600 feet) isobath around the islands of Maui, Molokai, Lanai; and including Penguin Banks ; the Pailolo Channel; and a small portion off Kilauea Point, Kauai. The Act also identified the waters around the island of Kaho'olawe to be included in the Sanctuary on January 1, 1996, unless the Secretary of Commerce certifies that those waters are not suitable for inclusion. The Secretary has certified that the waters around Kaho'olawe would not be included in the Sanctuary at this time. In 1997, this language was changed to provide the Kaho'olawe Island Reserve Commission and the State of Hawaii with the option of being included within the Hawaiian Islands Humpback Whale National Marine Sanctuary.

The Act allows the Secretary of Commerce, in consultation with the Governor of Hawaii, to make modifications to the boundaries of the Sanctuary as necessary to fulfill the purposes of the Act. As proposed in the Draft Environmental Impact Statement and Management Plan (DEIS/MP), NOAA has proposed to expand the Sanctuary to include the eastern portion of Kauai, North and South Oahu and the Big Island.