Individual variation in feeding habitat use by adult female green sea turtles (Chelonia mydas): are they obligately neritic herbivores?
- 748 Downloads
Satellite telemetry and stable isotope analysis were used to confirm that oceanic areas (where water depths are >200 m) are alternative feeding habitats for adult female green sea turtles (Chelonia mydas), which have been thought to be obligate herbivores in neritic areas (where depths are <200 m). Four females were tagged with satellite transmitters and tracked during post-nesting periods from Ogasawara Islands, Japan. Three females migrated to neritic habitats, while transmissions from another female ceased in an oceanic habitat. The overall mean nighttime dive depths during oceanic swimming periods in two females were <20 m, implying that the main function of their nighttime dives were resting with neutral buoyancy, whereas the means in two other females were >20 m, implying that they not only rested, but also foraged on macroplankton that exhibit diel vertical migration. Comparisons of stable carbon and nitrogen isotope ratios between 89 females and the prey items in a three-source mixing model estimated that 69% of the females nesting on Ogasawara Islands mainly used neritic habitats and 31% mainly used oceanic habitats. Out of four females tracked by satellite, two females were inferred from isotope ratios to be neritic herbivores and the two others oceanic planktivores. Although post-nesting movements for four females were not completely consistent with the inferences from isotope ratios, possibly due to short tracking periods (28–42 days), their diving behaviors were consistent with the inferences. There were no relationships between body size and the two isotope ratios, indicating a lack of size-related differences in feeding habitat use by adult female green turtles, which was in contrast with loggerhead sea turtles (Caretta caretta). These results and previous findings suggest that ontogenetic habitat shifts by sea turtles are facultative, and consequently, their life histories are polymorphic.
KeywordsLife history Ontogenetic habitat shifts Reptile Satellite telemetry Stable isotope analysis
We thank H. Suganuma and K. Narushima of Everlasting Nature of Asia (ELNA), the staff (Y. Iwata, Y. Horita, and M. Ogasawara) and volunteers of the Ogasawara Marine Center, M. Kaneko and the staff of the Club Noah Hahajima, and the fishermen of Chichijima and Hahajima Islands, for field assistance and logistical support. We also thank the Sea Turtle Association of Japan for supplying tags and equipment, and Y. Matsuzawa for discussion. T. Miyajima and Y. Umezawa of the Biogeochemistry Laboratory, Ocean Research Institute, University of Tokyo, assisted with the stable isotope analysis and allowed us to use their mass spectrometer. G.C. Hays provided useful advice on attachment of the transmitter and data analysis. M.J. Miller helped to improve the manuscript. Figure 1 was created by the Maptool at http://www.seaturtle.org. Two anonymous referees provided constructive comments on the manuscript. This work was partly supported by a Grant-in-Aid from the Japanese Society for the Promotion of Science (No. 15255003) to K.S. and a Grant-in-Aid for Creative Scientific Research (No. 12NP0201) from the Ministry of Education, Culture, Sports, Science and Technology of Japan to K.T. The experiments were conducted under licenses issued by the Ministry of the Environment and complied with the current Japanese laws.
- Baba N, Kiyota M, Suganuma H, Tachikawa H (1992) Research on migratory routes of loggerhead turtles and green turtles by the Argos system. Report on commissioned project for fishing boat scientist data analysis in 1991. Fisheries Agency of Japan, Tokyo, pp 100–106 (in Japanese)Google Scholar
- Baba N, Kiyota M, Suganuma H, Tachikawa H (1993) Research on migratory routes of loggerhead turtles and green turtles by the Argos system. Report on commissioned project for fishing boat scientist data analysis in 1992. Fisheries Agency of Japan, Tokyo, pp 86–99 (in Japanese)Google Scholar
- Bjorndal KA (1997) Foraging ecology and nutrition of sea turtles. In: Lutz PL, Musick JA (eds) The biology of sea turtles. CRC, Boca Raton, pp 199–231Google Scholar
- Bolten AB (2003) Variation in sea turtle life history patterns: neritic vs. oceanic developmental stages. In: Lutz PL, Musick JA, Wyneken J (eds) The biology of sea turtles, Vol II. CRC, Boca Raton, pp 243–257Google Scholar
- Brockmann HJ (2001) The evolution of alternative strategies and tactics. Adv Stud Behav 30:1–51Google Scholar
- Grafen A (1988) On the uses of data on lifetime reproductive success. In: Clutton-Brock TH (eds) Reproductive success. Studies of individual variation in contrasting breeding systems. University of Chicago Press, Chicago, pp 454–471Google Scholar
- Hatase H, Takai N, Matsuzawa Y, Sakamoto W, Omuta K, Goto K, Arai N, Fujiwara T (2002) Size-related differences in feeding habitat use of adult female loggerhead turtles Caretta caretta around Japan determined by stable isotope analyses and satellite telemetry. Mar Ecol Prog Ser 233:273–281CrossRefGoogle Scholar
- Hirth HF (1997) Synopsis of the biological data on the green turtle Chelonia mydas (Linnaeus 1758). US Fish and Wildlife Service Biological Report 97:1–120Google Scholar
- Japan Fisheries Resource Conservation Association (1999) Research on migratory routes and diving ecology of sea turtles. General report on commissioned project for conservation research of aquatic animals in 1994–1998. Vol 1. Japan Fisheries Resource Conservation Association, Tokyo, pp 1–90 (in Japanese)Google Scholar
- Kurata Y, Yoneyama S, Tsutsumi S, Kimura J, Hosokawa S (1978) Experiments to increase number of green turtles through the release of the young. Report on fundamental research for fisheries development in Ogasawara Islands. No. 3. Ogasawara Fishery Center, Tokyo Metropolitan Government, Tokyo, pp 58–80 (in Japanese)Google Scholar
- Limpus CJ, Limpus DJ (2001) The loggerhead turtle, Caretta caretta, in Queensland: breeding migrations and fidelity to a warm temperate feeding area. Chelonian Conserv Biol 4:142–153Google Scholar
- Maekawa K, Nakano S (2002) To sea or not to sea: a brief review on salmon migration evolution. Fish Sci (suppl I) 68:27–32Google Scholar
- McMahon CR, Autret E, Houghton JDR, Lovell P, Myers AE, Hays GC (2005) Animal-borne sensors successfully capture the real-time thermal properties of ocean basins. Limnol Oceanogr Methods 3:392–398Google Scholar
- Miyawaki I (1994) Sea turtles captured at the coast of Kushimoto Town, Wakayama Prefecture, and their straight carapace lengths. In: Kamezaki N, Yabuta S, Suganuma H (eds) Nesting beaches of sea turtles in Japan. Sea Turtle Association of Japan, Osaka, pp 75–80 (in Japanese)Google Scholar
- Musick JA, Limpus CJ (1997) Habitat utilization and migration in juvenile sea turtles. In: Lutz PL, Musick JA (eds) The biology of sea turtles. CRC, Boca Raton, pp 137–163Google Scholar
- Suganuma H, Horikoshi K, Tachikawa H, Sato F, Yamaguchi M (1996) Reproductive characteristics of the Ogasawara green turtles. In: Keinath JA, Barnard DE, Musick JA, Bell BA (eds) Proceedings of the 15th annual symposium on sea turtle biology and conservation. NOAA Technical Memorandum NMFS-SEFSC-387, pp 318Google Scholar
- Tachikawa H, Sasaki A (1990) Tagging study of adult green turtle in Ogasawara Islands. Umigame Newsletter of Japan 6:11–15 (in Japanese)Google Scholar
- Wang WL, Yeh HW (2003) δ13C values of marine macroalgae from Taiwan. Bot Bull Acad Sin 44:107–112Google Scholar