MOVEMENTS AND DISTRIBUTION OF HAMMERHEAD SHARK PUPS ON THEIR NATAL GROUNDS

Ultrasonic telemetry was used to determine the movements and distribution of juvenile hammerhead sharks (Sphyrna lewini) on their natal grounds in Kaneohe Bay, Oahu, Hawaii. Transmitters were force fed to six pups which were tracked for periods of up to 12 days. All animals showed a high fidelity to a shared daytime core area to which they repeatedly returned after exhibiting wider ranging nocturnal movements. During daytime, the shark pups formed a loose school which moved about within the core area, hovering about 1.5 m off the bay floor. This daytime refuging behavior may serve an antipredation function. Nighttime movements covered the bay floor and bases of patch and fringing reefs and probably represented foraging excursions. Occasional forays away from the core area also occurred during daytime. The small size of the total activity spaces may indicate a healthy forage base for the sharks. Nocturnal swimming speeds were greater than diurnal swimming speeds.