646 



Concurrent scavenging off a whale carcass by 

 great white sharks, Carcharodon carcharias, 

 and tiger sharks, Galeocerdo cuvier 



Sheldon F.J. Dudley 

 Michael D. Anderson-Reade 

 Greg S. Thompson 



Paul B. McMullen 



Natal Sharks Board 



P Bag 2 



Umhianga Rocks 4320, South Africa 



E-mail address (for S Dudley): dudley a shark co za 



The great white shark, Carcharodon 

 carcharias (Lamnidae), and the tiger 

 shark, Galeocerdo cuvier (Carcharhin- 

 idae), are two of the largest species 

 of macropredatory sharks. Both are 

 known to prey on dolphins (Delphini- 

 dae) off KwaZulu-Natal, South Africa 

 (Cockcroft et al., 1989). Although scav- 

 enging off whale carcasses by white 

 sharks (Carey et al, 1982; Pratt et al., 

 1982; McCosker, 1985; Long and Jones, 

 1996) and tiger sharks (Compagno et 

 al., 1998) has been documented, the 

 two species have not been recorded 

 feeding concurrently on the same car- 

 cass. In August 1993, Natal Sharks 

 Board (NSB) observers saw both spe- 

 cies feeding on the carcass of a hump- 

 back whale, Megaptera novaeangliae. 

 off Durban, but they were not seen scav- 

 enging concurrently (NSBM. In Sep- 

 tember 1997, elsewhere in the south- 

 west Indian Ocean, tiger sharks were 

 filmed feeding on a humpback whale 

 carcass off the southern tip of Mada- 

 gascar, but no white sharks were pres- 

 ent. Compagno^ subsequently viewed 

 the footage and verified the identifica- 

 tion of the tiger sharks. 



This paper presents observations of 

 white and tiger sharks scavenging off 

 the floating carcass of a Bryde's whale, 

 Balaenoptera edeni. off the coast of 



' NSB (Natal Sharks Board). 199.3. Un- 

 publ data. Natal Sharks Board, P. Bag 2, 

 IJmhIanga Rocks 4320, South Africa. 



'^ Compagno, L. J. V, 1999. Personal 

 commun. South African Muspum, P.O. 

 Box 61, Cape Town 8000, South .Africa. 



KwaZulu-Natal, South Africa. These 

 observations are of a single event and 

 hence should not be attributed more 

 significance than they can support. 



Methods 



The National Sea Rescue Institute 

 (NSRI) reported the presence of a 

 Bryde's whale carcass to the NSB at 

 midday on 26 April 1998. The NSRI, 

 which had responded to a call reporting 

 the carcass as a capsized yacht, found 

 it floating 4 km east of the Durban 

 harbor entrance ( 29°52'S, 31°24'E ) with 

 large sharks in its vicinity. The follow- 

 ing day various reports were received 

 that the carcass had drifted 25 km to 

 the north and was several kilometers 

 off the mouth of the Umdloti River 

 (29°38'S, 3r07'E). Large sharks were 

 reported to be feeding on it. 



On 28 April, three of the authors 

 launched a 5.5-iti open-deck boat, 

 equipped with photographic equipment 

 and a shark cage, from the beach at 

 Umhianga Rocks (29°43'S, 3r05'E). 

 The carcass was located 6 km offshore 

 of the launch site and 10 km south of 

 its position on the previous day. It was 

 observed for 5 h. Conditions were excel- 

 lent, with a glassy sea, light wind, little 

 current, an estimated water tempera- 

 ture of 23°C and clarity of 15 m. 



This account was written by S. F. J. 

 Dudley (who did not witness the event) 

 on the basis of separate interviews with 

 the remaining authors and on viewing 

 27 min of video footage filmed by M. 



D. Anderson-Reade and an additional 

 4 min of footage filmed from another 

 boat. All distances, times, and shark 

 lengths (precaudal length, PCD are 

 approximate. The carcass was identi- 

 fied to species from the video footage, by 

 the presence of prominent head ridges 

 (Peddemors-'). 



Results 



A white shark of 5 in was encountered 

 500 m from the carcass. The shark 

 made numerous passes within 2 m of 

 the stationary boat and just below the 

 surface. This behavior continued for 15 

 min before the boat continued towards 

 the carcass. This animal was not seen 

 again. 



Immediately upon reaching the car- 

 cass, two tiger sharks of 3.5 m were 

 seen cruising 3 m below the surface. 

 Two white sharks were present as well, 

 one of about 4 m and the other a larger 

 animal with a distinctive bite scar on 

 the right side, located dorsolaterally 

 and posterior to the first dorsal fin. 

 A second boat was present and both 

 shark species made approaches to each 

 boat. The shark cage was deployed and 

 occupied by two divers. A number of 

 tiger sharks with distended abdomens 

 were seen feeding on the carcass, usu- 

 ally singly but sometimes in groups of 

 two or more. Their approaches to the 

 carcass were leisurely and gave no evi- 

 dence of intraspecific aggression. The 

 white sharks, which were not seen feed- 

 ing during this period, moved off soon 

 after the cage was deployed and the 

 animal with the bite scar was not seen 

 again. 



For 20 min the boat and cage were 

 maneuvered around the carcass in an 

 attempt to film the feeding process. 

 Large quantities of organic debris 

 reduced water clarity and because vis- 

 ibility was better from the surface, the 

 divers returned to the boat and the 

 cage was retrieved. 



A 4-m female white shark, possibly 

 the smaller animal seen at the carcass 



' Peddemors, V. M. 1998. Personal com- 

 mun. Natal Sharks Board, P. Bag 2, Umh- 

 ianga Rocks 4320. .South Africa. 



Manuscript accepted 6 January 2000. 

 Fish. Bull. 98:646-649 (2000). " 



