Movement Patterns of Juvenile Loggerhead Turtles (Caretta caretta L. 1758) and Green Turtles (Chelonia mydas L. 1758) Hatched in Captivity and Released in the Korean Waters

Abstract

With most sea turtle populations declining, activities to conserve their habitat and nesting grounds and restore their populations are being implemented worldwide. To preserve the Northwestern Pacific populations, the National Marine Biodiversity Institute of Korea has been releasing artificially propagated sea turtles, but whether these individuals join the wild population remains unknown. The present study aimed to determine the movement patterns of artificially propagated juvenile loggerhead (Caretta caretta) and green (Chelonia mydas) turtles fitted with satellite transmitters on their carapaces and released in the waters of Jeju or Yeosu, Republic of Korea, between August 2018 and April 2022. Loggerheads traveled northward to the East Sea, whereas green turtles moved west or southwest. Two 36-month-old and two 48-month-old loggerheads moved toward their potential nursery grounds and toward their feeding grounds, respectively. Three green turtles with a curved carapace length (CCL) of <40 cm moved toward their nursery or feeding grounds, while three individuals (CCL > 45 cm) moved toward their inshore foraging areas. The travel paths were closely related to the direction of local sea currents. Our results implied that releasing artificially propagated sea turtles, considering their age and CCL, can positively contribute to the conservation of Northwestern Pacific populations.

Keywords: artificial breeding; restoration; satellite tracking; sea current; travel path.

Figure 1

Travel routes of satellite-tracked loggerhead turtles KOR0094 and KOR0096.

Figure 2

Travel routes of two satellite-tracked loggerhead turtles, KOR0108 and KOR0109. In the case of KOR0109, the dotted line between the release date and 10/29 (29 October) indicates a period when no tracking signal was received; the reasons for this are unknown.

Figure 3

Travel routes of four satellite-tracked green turtles. KOR0101 with a CCL less than 40 cm stayed in the Yellow Sea, while three turtles with CCLs over 40 cm traveled to the southwest.

Figure 4

Topography and typical current patterns in the North Pacific Ocean (with reference to References [61,62,63]). Red arrows indicate warm currents, blue arrows indicate cold currents, and black arrows indicate gyres. BPIOT, Branch of the Pacific-to-Indian Ocean Throughflow; EKWC, East Korean Warm Current; GDCC, Guangdong Coastal Current; NKCC, North Korea Cold Current; TWC, Tsushima Warm Current; YSCC, Yellow Sea Coastal Current; ZFCC, Zhejiang-Fujian Coastal Current.