The effect of flowing water on the locomotor behavior of nurse (Ginglymostoma cirratum) and lemon (Negaprion brevirostris) sharks and on the accuracy of localization of a chemical source by nursing sharks

Abstract

The locomotor behavior of juvenile nurse (Ginglymostoma cirratum) and lemon (Negaprion brevirostris) sharks were monitored automatically. The presence of flowing water (1.17 cm/s) was shown to affect the locomotor behavior in both species of shark. As compared to stagnant conditions, the locomotor variables velocity and frequency of turns tended to increase in the presence of flow. On the other hand, the average step lengths and variability of the frequency distributions for both velocity and angle classes decreased. Finally, a reversal in the ratio of right to left-handed turns made by nurse shark in response to flow was demonstrated. Furthermore, the presence of flow enhanced the accuracy of localization of discrete point sources of shrimp extract solution by the nurse shark. Although the chemical stimulus triggered rheotactic behavior, the steepness of the chemical gradient within the tank also played a role. It was postulated that both the presence of flow and the steepness of the chemical gradient interact and constitute jointly a new stimulus condition.