TRACKING OF ADULT MALE AND FEMALE
LOGGERHEAD SEA TURTLES BY
MEANS OF THE SATELLITE
BIOTELEMETRY SYSTEM

Wataru Sakamoto#1, Nobuaki Arai#1 and Norihisa Baba#2
#1: Faculty of Agriculture, Kyoto University
606-01 Kyoto, Japan
#2: National Research Institute of Far Seas Fisheries
5-7-1, Orito, 424 Shimizu, Japan

INTRODUCTION For the last decade, yearly nesting number of loggerhead turtles in the North Pacific Ocean are gradually decreasing. Adult female sea turtles land on sandy beach to lay eggs. The nesting beach is nearly same where they themselves hatched. The mechanism how turtles detect the same beach is unknown. Furthermore the behavior of adult males are hardly known since they never land throughout their lives. The purpose of this research is to know the migration paths of loggerhead turtles in the North Pacific Ocean using satellite tracking system. And these migration paths will be referred to sea turtle conservation program.

METHOD Three satellite transmitters (PTTs) were attached to 2 females (F-1, -2) and a male (M-1). Females were released from nesting beach, F-1 was released on July 28, 1995, F-2 was on August 3, 1996. The male was captured by a set net off the nesting beach on January 9, 1996 and released again 10 days after attaching a PTT. The locations were recorded for 4, 4, and 8 months respectively through Argos system. Migration paths were referred to earth's geomagnetic field, the sun orbital along with their paths.

RESULTS Two female turtles arrived at the same southwestern feeding ground, the East China Sea, soon after the nesting season. However the migration path was different; F-1 migrated southern side of the Kuroshio, while F-2 moved northern side of the Kuroshio along Japan Island. The courses were separated by the prevention from strong against northeastern current. Total migration distance were about 1500 km. The male turtle migrated in southern warm water areas during spring season. Five months later from release, in early summer, it returned to coastal zone neighboring the nesting beach to mate with females. It migrated about 2000 km in total before arriving again at the nesting beach.

DISCUSSION The sun orbital was suggested the possible method to detect the temporal progress in the ocean. Similar sunrise hour was shown for F-1 in the periods of its returning to the East China Sea. The similar sunset hour was shown for the male turtle when it began to return to the nesting beach. We think the earth's geomagnetic compass is not so available for the turtles to know the seasonal or temporal transition in the ocean.