Fishes appear well oriented in their movements in the oceanic environment, but the mechanisms they use for orientation or navigation are very poorly understood. Dr. Klimley is investigating these mechanisms with the scalloped hammerhead shark (Sphyrna lewini). Using ultrasonic telemetry, he has identified two oriented behavioral responses, straight-line swimming and homing (i.e., repeated movements away from and back to residence), at seamount El Bajo Espiritu Santo in the Gulf of California. He now is seeking to determine what environmental cues sharks use to carry out these behaviors by correlating an increase in the directionality of their swimming movements with the presence or absence (or strong gradient) of an environmental feature. Instantaneous swimming directions, depths, surrounding water temperatures, and light levels will be recorded continuously by a computerized data-logging system. Dr. Klimley will obtain the following environmental measurements: (1) vertical profiles of current directions and speeds, water temperatures, and light levels periodically along the shark's swimming path, (2) sea-surface temperatures from satellite images, and (3) a flower-petal-shaped survey pattern of bottom topography, total magnetic fields, and local field differences from the earth's average field. He will determine whether or not the straightness or directionality of shark tracks or instantaneous swimming movements are correlated with any of the above features. The research will focus, in particular, on magnetic-field features because preliminary results indicate possible utilization by hammerhead sharks. An important outcome of identifying those environmental features to which fish orient is that mapping of the environment would then enable prediction of those locations where fish densities are highest. Such a capability would increase the capture success of fisheries.
