RANDALL: SURVEY OF CIGUATERA AT MARSHALL ISLANDS 



bacora (= Thunnus albacares). Bass et al. (1973) 

 examined the stomach contents of 10 specimens of 

 C. albimarginatus from the western Indian Ocean. 

 They found teleost fishes (exocoetid, myctophid, 

 several soleids) in seven sharks; a spotted eagle 

 ray, Aetobatis narinari, in one; and an octopus in 

 one. 



The stomach of one of the Enewetak silvertips 

 (1,240 mm PCL, 1,650 mm TL) contained a gray 

 reef shark, Carcharhinus amblyrhynchos , 483 mm 

 PCL and 616 mm TL, as well as the dental plates 

 and pharyngeal mills of three parrotfishes 

 (Scarus). The stomachs of the other three sharks 

 were empty. 



Carcharhinus amblyrhynchos (Bleeker) Figure 

 3): This shark, now popularly known as the gray 

 reef shark, was referred to by Schultz in Schultz 

 and collaborators (1953) as Carcharhinus 

 menisorrah (Miiller and Henle). Bass et al. (1973) 

 and Garrick (in press) are followed in the use of the 

 name C. amblyrhynchos herein. 



The gray reef shark lacks dark pigment distally 

 on the first dorsal fin, but the tips of the other fins 

 are broadly blackish, and there is a broad black 

 margin posteriorly on the caudal fin. The dark 

 markings on the fins are more evident on live than 

 on dead specimens. The origin of the first dorsal fin 

 is over the pectoral axil or anterior part of the 

 inner edge of the pectoral fin. A short interdorsal 

 ridge is present or absent. There are 26-28 upper 

 teeth and 24-26 lower teeth; the precaudal verte- 



brae vary from 110 to 117 (two Enewetak speci- 

 mens had 117). 



This shark is abundant in the Marshall Islands. 

 It occurs in many habitats from lagoons to ocean 

 reefs, but it is most commonly encountered in deep 

 channels and outer reef areas. It does not pene- 

 trate the shallows as readily as C. melanopterus. 



The flesh of 11 specimens from Enewetak, 

 1,017-1,190 mm PCL (17.2-26.3 kg), and 1 from 

 Bikini (3.6 kg, length not taken) was tested. All 

 gave a zero reaction for ciguatoxin. The viscera of 

 one of these, 1,158 mm PCL, from Enewetak pro- 

 duced a reaction of 2, however. 



The stomachs of 74 individuals, 520-1,230 mm 

 PCL (2.7-32.4 kg), from Enewetak, Fanning and 

 Palmyra in the Line Islands, Marcus Island, 

 Johnston Island, Palau Islands, and Ducie and 

 Henderson in the Pitcairn Group, were examined 

 for food. Forty-nine stomachs were empty or con- 

 tained only bait. Three had eaten cephalopods 

 (two octopus, one squid), and the rest contained 

 the remains of fishes (in some cases only the lens of 

 an eye or a few remnants of spines or bones). The 

 fishes that could be identified to family or genus 

 were the following: muraenid, belonid, exocoetid, 

 Fistularia, Decapterus , Trachinotus, Acanthurus, 

 and another acanthurid (either Acanthurus or 

 Ctenochaetus). 



In spite of its relatively small size, the gray reef 

 shark constituted a hazard to the personnel of the 

 survey program, particularly when divers were 

 spearfishing or collecting with rotenone. Several 



Figure 3.— Carcharhinus amblyrhynchos, 1,288 mm PCL, 1,640 mm TL, Tahiti, Society Islands. 



207 



