NOTE Dudley et aL: Scavenging off a whale carcass by Carcharodon carcharias and Galeocerdo cuvier 649 



noted that feeding attempts by individual white sharks 

 may be thwarted by larger conspecifics. In our study, 

 although three, possibly four, white sharks were seen at 

 or near the carcass, only one was seen feeding. Although 

 the observation period was brief, this type of behavior is 

 consistent with the existence of intraspecific competitive 

 exclusion. The animal seen feeding was smaller than at 

 least two of its conspecifics, and it is possible that the 

 larger individuals had fed previously. 



The tiger sharks exhibited no evidence of intraspecific 

 competition, despite the presence of up to 10 individuals 

 in the vicinity of the carcass and up to five feeding concur- 

 rently. The abundance of food or the similarity in size of 

 the sharks may have prevented the establishment of the 

 size-dependent hierarchy discussed by Bres (1993). 



Interspecific competition for food amongst reef-dwelling, 

 carcharhinid species has been recorded (Nelson and John- 

 son, 1980), as have apparent interspecific hierarchies com- 

 prising 1 ) the silvertip shark, Carcharhin us alblmarginatiis. 

 the Galapagos shark, C. galapagensis, and the blacktip 

 shark, C. limbatus. ( Limbaugh, 1963 ); 2 ) the oceanic whitetip 

 shark, C. longimanus. and the silky shark, C. falciformis; 

 and 3) hammerhead sharks (Sphyrnidae) and various other 

 species (Springer, 1967). Pratt et al. (1982) noted that the 

 locally abundant blue shark, Prionace glaiica, and shortfin 

 mako. Isuriis oxyrinchus. were conspicuously absent from 

 the vicinity of the fin whale carcass, and a fish spotter 

 pilot observed no blue sharks within a 3.2-km radius. These 

 authors suggested that this was a consequence of territorial 

 exclusion by white sharks. Similarly, Long and Jones ( 1996) 

 suggested that white sharks excluded blue sharks, a spe- 

 cies known to scavenge on whale carcasses, from the blue 

 whale carcass. McCosker (1985) observed a single white 

 shark feeding on the carcass of a grey whale, Eschrichtius 

 rohnstus. and saw no other shark species nearby The white 

 and tiger sharks, however, did not appear to compete at the 

 Bryde's whale carcass. Springer (1967) noted that mixed- 

 species feeding aggregations tend to consist of sharks of 

 similar sizes. If it is hypothesized, therefore, that the single 

 4-m white shark would have competitively excluded a single 

 3..5-m tiger shark, the presence of several tiger sharks may 

 have prevented this from occurring. McKibben and Nelson 

 ( 1986) speculated that juvenile gray reef sharks grouping in 

 a loose aggregation or as a polarized pack may obtain pro- 

 tection from larger sharks. The tiger sharks, attracted by a 

 single stimulus, may have derived an incidental defensive 

 benefit. 



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