Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
The grey reef shark (C. amblyrhynchos), blacktip reef shark (C. melanopterus), whitetip reef shark
(Triaenodon obesus), and Galapagos shark (Carcharinus galapagensis) are categorized by the IUCN
as a lower risk but near threatened species; whereas the tiger shark (Galeocerdo cuvier) is near
threatened (Heupel 2000; Simpfendorfer 2000; Smale 2000a, 2000b; Bennett et al. 2003). All of the
requiem sharks are afforded protection under the Shark Finning Protection Act (NMFS 2002).
Distribution—The requiem sharks comprise one of the largest and most important shark families.
These species are common, wide-ranging, and can be found in all warm and temperate seas
(WPRFMC 2001).
In the western Pacific, the grey reef shark ranges from southern China to northern Australia and the
Tuamoto Archipelago (Compagno 1984).
The silvertip shark ranges from off southern Japan to northern Australia and French Polynesia
(Compagno 1984).
The Galapagos shark is circumtropical in distribution with a preference for waters surrounding
oceanic islands. In the tropical regions of the Pacific, the Galapagos shark can be found around Lord
Howe Island, the Tuamoto Archipelago, Middleton and Elizabeth Reefs, Hawai’i, Revillagigedo,
Clipperton, Cocos, and the Galapagos Islands (Compagno 1984).
In the western Pacific, the blacktip reef shark ranges from South Africa, the Red Sea, Pakistan, and
India eastward to the western Central Pacific (Compagno 1984).
The whitetip reef shark is common in Polynesia, Melanesia, and Micronesia, northward to the
Hawaiian Islands, and southwest to the Pitcairns (Compagno 1984).
Habitat Preferences—Most species of requiem sharks inhabit tropical continental coastal and
offshore waters, but several species prefer coral reefs and oceanic islands (Compagno 1984).
Requiem sharks inhabit a wide variety of coral reef habitats with no apparent preference.
Grey reef sharks prefer open water, above reefs, particularly along steep outer slopes or dropoffs at
depths from 1 to 274 m. This species is common around the islands of the northern Marianas and
Micronesian atolls where it frequents lagoons, channels, and seaward reefs (Myers 1999).
Silvertip sharks are typically found over dropoffs and offshore banks at depths of 30 to 400 m but
have been observed in lagoons, deep channels, and surface waters (Myers 1999). Adult Galapagos
sharks can be found over steep outer reef slopes and offshore banks at depths of 30 to 180 m.
Juveniles are more commonly found in waters between 2 and 25 m (Myers 1999).
Blacktip reef sharks are common inshore and occasionally offshore on continental and insular
shelves. This species is generally associated with reef flats, shallow lagoons, and reef margins
(Compagno and Niem 1998).
The whitetip reef shark is one of the most common sharks in lagoons and over seaward reefs and is
frequently found resting on the bottom over sand patches. This species is generally found at depths
greater than 3 m and has been observed as deep as 300 m (Compagno and Niem 1998; Myers
1999).
Life History—Carcharhinid sharks reproduce by internal fertilization, and all but one species (tiger
shark) in this family are placental viviparous (embryos are nourished by a placenta like organ in the
female) (WPRFMC 2001). Juvenile carcharhinids are often associated with inshore areas such as
bays, seagrass beds and lagoon flats but move into deeper waters as they mature. Adult sharks
frequent inshore areas during mating or birthing events and on occasion for foraging (WPRFMC
2001).
4-21