230 Shark and Company 



to be unable to discern colors because the retinas of the eyes of most 

 species do not seem to have color-perceiving cones. Recent experiments 

 conducted by Dr. Eugenie Clark indicated, however, that at least one 

 shark was violently repelled by the color yellow. The experiments were 

 performed at the Cape Haze Marine Laboratory at Sarasota, Florida. 

 Dr. Clark was working with 8-foot Lemon sharks (Negaprion breviros- 

 tris) enclosed in a pen next to a dock, trying to train them to push a 

 "target" for food. One shark, trained to a white target, hungrily dashed 

 toward it, as usual, one day. But Dr. Clark had substituted a yellow tar- 

 get to test the shark's color perception. A few feet from the target. Dr. 

 Clark reported, the shark whirled, did a back flip out of the water and 

 then began going crazily around in circles. Transformed into what ap- 

 peared to be a very neurotic shark, it refused to eat, and soon died. 



Did the mere sight of yellow do all this? Neither Dr. Clark nor any- 

 one else knows. Certainly yellow isn't that repulsive to other sharks, for, 

 during World War II, many yellow life-rafts were nudged and some- 

 times attacked by sharks. 



Aristotle, a pioneer fish-watcher, said that fish could hear, "for they 

 are observed to run away from any loud noises like the rowing of a gal- 

 ley." There have been times when marine biologists were not as posi- 

 tive as Aristotle that fish could hear, but in relatively recent times dis- 

 coveries have been made which clearly demonstrate that fish can hear, 

 and can discriminate pitch. Little, however, is known about the hearing 

 of sharks in particular. There seems to be little doubt that Selachians 

 can hear, or at least pick up vibrations accompanied by what humans 

 sense as sound. Selachians respond to vibrations, such as the pulsations 

 of a steamer's screws in the open sea, or the ringing of an underwater 

 bell in a laboratory experimental tank. And they do appear to have ears- 

 inside their heads. 



The question of how sharks can detect prey at considerable dis- 

 tances has long fascinated both fishermen and marine biologists. Neither 

 vision nor the sense of smell can explain some of the amazing prey- 

 detection performances sharks have put on before observers' eyes. Al- 

 though there is no doubt that the shark's super-sensitive olfactory system 

 can detect minute quantities of blood whose odor is carried toward them 

 by currents, the sense of smell alone cannot explain how sharks can track 

 prey whose scent or blood is being carried away from the shark by cur- 

 rents. Nor can vision alone be the sense sharks use to find prey that is 

 behind obstructions, such as rocks. (Skin-divers have reported many 

 such incidents.) 



Somehow, sound or vibration detection would seem to be the answer 

 to these mysteries. Dr. Warren Wisby of the Institute of Marine Science 

 at the University of Miami has been seeking the answer in a long-range 



