DIURNAL SWIMMING PATTERNS OF WHITETIP
REEF SHARK, TRIAENODON OBESUS, AS
OBSERVED BY BIO-RECORDER SYSTEM

Kazunari Yano^*, Osamu Abe^*, Yoshitake Takada^*, Minoru Toda^**, and Senzo Uchida^**
*Seikai National Fisheries Research Institute, Ishigaki Tropical Station,
Fisheries Agency of Japan, 148-446 Fukai Ota, Ishigaki, Okinawa 907-04, JAPAN
^**Okinawa Expo Aquarium, 424 Ishikawa, Motobu-cho, Okinawa 905-03, JAPAN

INTRODUCTION Whitetip reef shark, Triaenodon obesus, is a common species of tropical inshore of the continental shelves and island terraces, frequently found near the bottom, resting in caves or under coral ledges during daytime. The whitetip reef shark appears to have a narrow home range, moving within a radius of only a few kilometers. This study presents the diel swimming patterns of captive whitetip reef shark in swimming tank of an aquarium, which were measured by bio-recorder system.

MATERIALS AND METHODS Adult-size whitetip reef shark, Triaenodon obesus, was captured in a swimming tank of the Okinawa Expo Aquarium and was used in the present study during from 3-24 December, 1994. The diel swimming patterns of whitetip reef shark were measured with a time-depth recorder and time-illumination recorder (bio-recorder system, 18 mm in diameter, 109 mm in length, 284 g in air, and 3.5 g in water). The time-depth and time-illumination recorders were attached to first dorsal fin of the shark.

RESULTS AND DISCUSSION This reef-associated shark was usually found near the bottom, sometime resting in caves or under coral ledges-like areas in the swimming tank during the day. This study indicate that it is more active at night. The diel swimming patterns are probably adapted to feeding behavior, particularly active swimming in home range areas during nighttime and crevices and holes in the coral during daytime, where it catches small fish, crustaceans and octopus.