SENSORY BIOLOGY: PACIFIC SHARKS 603 



(Pardachirus marmoratus) produces a mucus which repels sharks (Clark and 

 Chao 1973). Pardachirus and a closely related genus (Aseraggodes) occur 

 along the eastern coast of Australia, but no local observations of their shark- 

 repelling capacities were encountered. However, another fish (Diploprion 

 bifasciatum) is known to exude abundant and bad-tasting mucus when dis- 

 turbed, and in several localities of the Northern Territory and Great Barrier 

 Reef it is reported to repel sharks and other potential predators. Several 

 invertebrate animals, especially holothurians (Bakus 1973), are used in 

 Micronesia to poison fish, including sharks, and observations of their avoid- 

 ance by sharks are common. 



To date, no systematic or controlled studies have been carried out of 

 fauna which might be producing "natural repellents" in the South Pacific. 

 Even with the most frequently encountered claims about this matter, no 

 data of a scientific nature appear to exist. For example, in Micronesia and 

 northeastern Australia, one encounters claims that the "ink" squirted during 

 escape and protective behavior by octopi repels predators, including sharks. 

 A tank label in the Honolulu Aquarium goes so far as to claim that octopus 

 ink ". . .deadens the predator's sense of smell." If true, this would have 

 obvious physiological and practical importance, but local scientists were un- 

 aware of any adequate studies conducted on the possibility (Tester, personal 

 communication). This should be a fertile area for future investigation in 

 marine pharmacology, toxicology, and behavioral studies. 



RECOGNITION OF BEHAVIOR PATTERNS IN SHARKS 



Many Pacific Islanders show an awareness of shark behavior patterns, and an 

 ability to discriminate among them, that seems uncanny. Identification of 

 species and activity patterns on the basis of their swimming sounds under- 

 water, mentioned above, is only one example. Visual recognition of shark 

 activity patterns is also acute. 



Benchley (1873), in one of the earliest documentations of this matter by a 

 European explorer in the South Pacific, was puzzled by the fact that local 

 swimmers did not always bother to avoid sharks. Between Tonga and 

 Palmerston Island, he encountered an instance when islanders swam 

 ". . . among them (tiger sharks) without manifesting any apprehension." The 

 implications of this appeared to be that the islanders knew when the tiger 

 sharks were in an aggressive "mood," or possibly that the sharks were not 

 ". . . as dangerous as they are supposed to be." (It is difficult to imagine how 

 Brenchley could have drawn the latter conclusion when the frontispiece of 

 the book shows a particularly gory painting, from the Solomon Islands, of 

 shipwrecked men doing battle with, and being eaten by, sharks!) That aggres- 

 sive behavior can be anticipated or predicted by watching the behavior of 

 potentially dangerous sharks is confirmed by experienced fishermen in many 

 parts of Micronesia. Bending of the back and extension of the pectoral 

 fins of a large shark are considered warning signals of imminent attack, 

 and prompt divers to leave the water, although they might have appeared 



