4 PERSPECTIVE 



migration from North Carolina coastal waters and when they will arrive off 

 the coast of northern Maine and Newfoundland. Likewise, we can predict 

 the time of their return in the fall (Templeman 1944, Jensen 1966). Olsen 

 (1954, 1959) has established the migratory movements of the edible 

 Australian school shark (Galeorhinus Australis), which has been a boon 

 to commercial fishermen. 



The movements of several species, including dusky (Carcharhinus ob- 

 scurus), sandbar (Carcharhinus milberti), lemon (Negaprion brevirostris), 

 bull (Carcharhinus leucas), and nurse sharks (Ginglymostoma cirratum), 

 along the gulf coast of Florida are predictable (Clark and von Schmidt 

 1965). This knowledge has been of great help to the collecting crew of 

 the Mote Marine Laboratory in Sarasota, Florida. The time of birth and 

 mating is also now well known for several species, including nurse sharks 

 (Ginglymostoma cirratum) at Dry Tortugas, Port Jackson sharks (Hetero- 

 dontus portusjacksoni) in Australia (McLaughlin and O'Gower 1971), 

 and sandbar sharks (Carcharhinus milberti) off the east coast of Florida 

 (Springer 1960, 1967). The gestation periods of certain viviparous sharks 

 are now well established; one species, Squalus acanthias, holds the verte- 

 brate record— an incredible 20-22 months (Hisaw and Albert 1947, Gilbert 

 and Heath 1972). 



Much has been learned about shark behavior in the past 20 years, and 

 many of their responses can now be predicted. The agonistic display of 

 the gray reef shark (Carcharhinus menisorrah) (Johnson and Nelson 1973) 

 warns the diver who encounters it. The attraction of several species of 

 sharks to low-frequency sounds, simulating those of struggling fish, has 

 been well established by Evans and Gilbert (1971), Nelson and Johnson 

 (1972), Brown (1973), and Myrberg et al. (1975), among others. The 

 orientation patterns of lemon sharks (Negaprion brevirostris) and nurse 

 sharks (Ginglymostoma cirratum) to specific chemicals of known dilution 

 are predictable (Mathewson and Hodgson 1972). 



While fresh fish and mammalian blood are moderately strong attractants 

 to several species, fresh tuna or bonito juice has repeatedly proved even 

 stronger. Even with such attractants it is often difficult to get captive sharks 

 to begin feeding. Once one shark in a group has rushed at a bait, however, 

 others quickly follow and a "feeding frenzy" often develops. Such active 

 competition for food and other desirable items is not restricted to the 

 elasmobranch level! 



The attraction of many species of sharks by bright or shining objects 

 is predictable. For this reason, dark, nonreflective colors have been recom- 

 mended for the submerged portion of shark deterrents such as the Johnson 

 Shark Screen (Gilbert 1968a) and the Federal Aviation Administration's 

 infant floatation device (Gilbert 1970). The responses of many species 

 of sharks to electric fields are well known and predictable, and Kalmijn 

 (1971) has demonstrated that Scyllorhinus canicula, using the ampullae 

 of Lorenzini as electroreceptors, can locate living prey, even if the prey 

 lies buried in the sand. Many other examples of predictable shark behavior 



