Diving Patterns and Swimming Environment of Two Loggerhead Turtles during Internesting

Abstract

Adult female loggerhead turtles land on sandy beaches in the Japanese archipelago to nest in a period during early summer to autumn. They lay eggs three times intermittently in the sand at about 20-day intervals. The swimming behavior of two turtles, Nos. 1 and 2, during these internesting periods was measured using new developed self-recording apparatus: time depth recorders (TDRs), time temperature recorders (TTRs), and time light intensity recorders (TLRs). The apparatus were attached to the carapace after the turtles' first or second nesting and recovered at the next landing. The time series data were compared with the environmental conditions. Typical diving behavior was ascertained by numerical factors based on the maximum depth attained and underwater duration. Median underwater duration of the dive was different in each individual, viz. 36.5 min for No. 1 and 25.5 min for No. 2. Meanwhile median maximum depth was 11m for No. 1 and 23.5m for No. 2. This dive was frequently found in No. 1. The swimming behavior of No. 2 was characterized by a high water temperature, which was due to offshore migration. Different behavior was suggested from daily changes in dive types and water temperature encountered by two turtles; No. 1 swam along the coastal zone near the nesting beach, while No. 2 swam further offshore and was transported by the Kuroshio current before returning again to the same nesting beach.