Home > Islets > Oahu > Mokumanu ISLETS: OAHU > MOKUMANU Mokumanu   Mokumanu - Photo: R Shallenberger Mokumanu - Photo: H Eijzenga   Mokumanu - Photo: H Eijzenga Mokumanu - Photo: F & K Starr   Mokumanu - Photo: F & K Starr Physical Features Mokumanu is composed of two steep, rocky islets separated by a narrow channel but connected underwater by an eroded lava dike. The combined area is 21 acres and it reaches a maximum height of 202 feet. Mokumanu is an eroded remnant of a volcanic tuff cone. It was formed from lava, pumice, cinder, and spatter originating from an old volcanic vent located near the small outer islet. Mokumanu is separated from Mokapu Peninsula by a deep, turbulent, 3/4 mile wide channel . Wave action created a large sea cave along the northwestern side of the island and several other smaller caves and caverns. Steep cliffs and rough seas make boat landings almost impossible. Regulations State regulations prohibit landing on either of the Mokumanu islets. In addition, the airspace and waters around Mokumanu are controlled by the Kaneohe Bay Marine Corps Base and all requests to enter the area must first be approved by the base. Mokumanu is a State Seabird Sanctuary managed by the Hawaii DOFAW. Regulations in Hawaii Administrative Rules, Title 13 Chapter 125, protect wildlife and plants and restrict human activities in seabird sanctuaries. Federal law also protects seabirds, shorebirds, and threatened or endangered species. Birds Mokumanu's inaccessibility accounts for the consistent large size and high species diversity of its seabird colony. Its name translates as ‘Bird Island,’ perhaps indicating its importance to seabirds even in ancient times. Bird surveys at Mokumanu date back to an 1889 visit by George Munro. Several surveys have been conducted on an irregular basis since then, up to the most recent one in February 2006. Twelve seabird species have been documented to breed on Mokumanu, including large numbers of Sooty terns (Sterna fuscata), Brown noddies (Anous stolidus), Wedge-tailed shearwaters, and Red-footed boobies (Sula sula). It seems likely that red-footed boobies shift back and forth between Mokumanu and the nearby booby colony at Mokapu Peninsula in Ulupau Crater. Although the total number of all breeding seabirds using Mokumanu over the course of a year is hard to estimate, a 1965 count of sooty terns alone estimated 50,000 adults. Mokumanu, along with Kaula, Lehua, and Manana, is among the most important seabird islets in the main Hawaiian Islands. Plants The 2006 survey found 14 plant species, 5 of which were native. The islets were sparsely vegetated but the 5 native species made up the majority of the plant cover. Aweoweo (Chenopodium oahuense) and Nohu (Tribulus cistoides) were the dominant natives. Aweoweo shrubs are a favorite nesting habitat for Red-footed boobies. In 2003, the U.S. Fish and Wildlife Service designated critical habitat on Mokumanu for the endangered plant, Chamaesyce kuwaleana. Although this plant was last seen on Mokumanu in 1937, re-establishing a population would be an important step towards species recovery. Insects The 2006 survey collected 22 species of insects, almost all of them alien species. Big headed ants (Pheidole megacephala) are present. This aggressive species often eliminates native insects. Marine Organisms Monk seals occasionally use Mokumanu to haul out. Because of rough water and the exclusionary zone created around Mokumanu by the military, fishing pressure is less intense than other areas and divers report an abundance of fishes not seen elsewhere. Tiger sharks and even a great white shark have been reported. Human Uses During World War II, Mokumanu was used for military target practice by planes from the Kaneohe Air Station. It was designated as a bird sanctuary in 1945. No current human uses are known. Threats The main threats are invasive weeds and ants, erosion of sparsely vegetated areas, and loss of shrubs used by nesting seabirds due to periodic droughts. Polynesian rats (Rattus exulans) were reported to be abundant and were trapped for identification in 1967 but they have not been reported since then. It is possible that they are still present but undetected. > Back to top of page Home  Islets  Species  Projects  Outreach  Links  About Us