318 



CHEMICAL SENSES 



Figure 33 Negaprion brevirostris: locomotor track in monitor tank II 

 with water flowing only in the central "channel" at 1.75 cm/s, as 

 indicated by arrows. After Maynard (1976). 



"tighten" the pattern after onset of the flow, as is evident from Figure 35, in 

 which the record of the first 12 min of another lemon shark is broken up 

 into periods of 3-5 min. 



In parallel experiments, nurse and lemon sharks were tested in Monitor I 

 (cylindrical tank with 16 free-choice compartments) in which various flow 

 conditions were created in one or more compartments to ascertain the spon- 

 taneous locomotor responses to such conditions. Both species discriminated 

 flow rates at least as low as 0.1 cm/s, but they responded differently. The 

 nurse shark remained significantly longer in the compartment without flow, 

 whereas the lemon shark responded by more frequently entering compart- 

 ments with flow. With one exception, difference in behavior was consistent. 

 This surprisingly high sensitivity to flow in both species might be mediated 

 by the lateral-line, electroreception, or both systems in concert. The above 

 experimental approach, by monitoring locomotor behavior, provides a sensi- 

 tive test for the study of this aspect of the problem. 



Gruber (1976) found that flow increased the swimming velocity of both 

 lemon and nurse sharks. Turning behavior was always affected by changes in 

 turning frequency and step length. 



