GRAY WHALES, Eschrkhtius robustus, AVOID THE UNDERWATER 

 SOUNDS OF KILLER WHALES, Orcinus orca 



William C. Cummings and Paul 0. Thompson' 



ABSTRACT 



Underwater sound playback experiments were undertaken to determine if gray whales would avoid the 

 sounds of killer whales. When presented killer whale "screams" from an underwater projector, the 

 gray whales swam directly away from the sound source. Controls of no intended stimulus, pure tones, 

 and random noise generally failed to induce an avoidance. It appeared that gray whales localized the 

 killer whale sounds and avoided them as a sign of potential danger. 



Killer whales, Orcimis orca, are known to attack 

 large marine mammals, including gray whales, 

 Eschric.hthis robustus (Scammon, 1874; More- 

 john, 1968). Several accounts of such attacks 

 were related to the first author by observers who 

 witnessed these events. Among these were Dr. 

 Carl L. Hubbs of Scripps Institution of Ocean- 

 ography, University of California, and Alan 

 Baldridge, Hopkins Marine Station, Stanford 

 University. In January 1952, Dr. Hubbs saw a 

 gray whale that swam into the thick kelp beds 

 off La Jolla, Calif., apparently fleeing from a 

 group of killer whales. Off the Point Lobos 

 State Reserve, Carmel, Calif., Baldridge ob- 

 served a gray whale calf being eaten by six to 

 seven killer whales. Other observers had seen 

 the initial attack which also involved the mother 

 whale. When Baldridge arrived, the killer 

 whales were chewing on the lips, tongue, and 

 throat of the dead young gray whale. 



Killer whales produce a variety of underwater 

 phonations, including high pitched "screams" 

 and trains of well-separated clicks (Schevill and 

 Watkins, 1966). Underwater sounds have been 

 recorded from about one-half of the known spe- 

 cies of marine mammals, and probably all are 

 capable of some vocal behavior. However, ex- 

 cept for the echolocating abilities of porpoises 

 and a few of their own behaviors associated with 

 sound pi'oduction, very little is known about the 



* Naval Undersea Research and Development Center, 

 San Diego, Calif. 92132. 



significance of underwater sound to marine 

 mammals — virtually nothing where the large 

 whales are concerned. 



Taking advantage of the gray whales' migra- 

 tion in nearby waters, we conducted underwater 

 sound playback experiments to find out if they 

 would react to the underwater sounds of killer 

 whales, possibly avoiding them as a sign of 

 danger. 



METHODS 



The experiments took place off Point Loma, 

 San Diego, Calif., during successive migrations 

 of gray whales in January 1969 and 1970. Each 

 year about 11,000 of these whales pass San Diego 

 on their southward migration to the breeding 

 grounds off Baja California and the Mexican 

 mainland (Rice, 1970). The whales, some with 

 calves, return to our waters in the early spring 

 on their way back to the Bering Sea and the 

 Arctic Ocean. 



Field work was done from a large catamaran, 

 RV Sea See, which served as a stable and roomy 

 platform, moored in 30 m of water, 33 m sea- 

 ward of an extensive kelp bed. The ship held 

 a northerly heading at the mooring. Gray whales 

 normally funneled through this location staying 

 relatively close to the coast, but avoiding the 

 thick kelp. 



Three kinds of acoustic stimuli were prepared 

 on magnetic tape — a natural sequence of 

 "screams" from killer whales, originally record- 



Manuscript accepted March 197], 



FISHERY BULLETIN; VOL. 69, NO. 3. 1971. 



525 



