Contribution to the Biology of the Whitetip Reef Shark (Triaenodon obesus)

摘要

The whitetip reef shark, Triaenodon obesus (Ruppell), is broadlydistributed in t4e tropical and subtropical Indian and Pacific oceans from theRed Sea (type locality) and east coast of Africa to the eastern Pacific. Formerlyclassified in the Triakidae, it is now regarded as a carcharhinid. It is distinctivein its slender body (depth about 7 in precaudal length), obtuse snout, 43 to 50teeth in each jaw in at least two functional rows, the teeth with one or twosmall cusps on each side of the large central cusp, and white tips on at leastthe first dorsal fin and upper lobe of the caudal fin. It is closely associated withcoral reefs and is often seen at rest in caves. There is evidence that this sharkhas a home cave to which it may return after foraging for food. Althoughreported to attain a total length of 7 feet (213 em) or more, the largest of 231individuals measured by the author and associates was 168 em total length(135 cm precaudal length). Seven recoveries were made of 124 whitetips taggedat Johnston Island (time at liberty with tags 16 days to 2 years). Two of thetagged sharks were caught in the same area as that in which they were releasedand the others were taken .3 to 2.9 km from the tagging sites. The growth rateof the tagged sharks, which ranged from 81 to 105 em precaudal length, variedfrom 2.1 to 4.2 em/year. Two captive sharks, 73 and 88 em precaudal length,grew at the rate of 4 and 2.3 cm, respectively, in the Gulf of Aqaba, Red Seaover a period of 3 years. A whitetip born in captivity in July at a precaudallength of 43.2 cm at Enewetak, Marshall Islands, grew 2 em in 6 weeks. Thestomachs of 56 whitetips were opened; 33 were empty; 17 contained the remainsof fishes (those identified were all reef fishes such as scarids and acanthurids);four had eaten octopuses, and two contained both fishes and octopuses. Onereference described a diet of xanthid crabs and spiny lobsters. A juvenilewhitetip was found in the stomach of a larger grouper (Epinephelus lanceolatus);some of the larger sharks such as the tiger and Galapagos sharks are probablymore important predators than this grouper. The sex ratio does not deviatesignificantly from 1 : I except for whitetips caught in traps; 65 of 107 trap-caughtsharks were males. The smallest mature female T. obesus of this study measured101.2 cm precaudal length (but a smaller size might be expected), and thesmallest mature male was 82 cm. Litter size ranges from one to five. Comparedto other carcharhinids, T. obesus is a relatively placid species which need notbe feared by divers unless provoked or attracted by spearfishing (even thenaggressive behavior toward man is rare). This shark may cause ciguaterapoisoning, especially if the liver is eaten.