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Marine Biology

, 166:25 | Cite as

Diverse foraging habits of juvenile green turtles (Chelonia mydas) in a summer-restricted foraging habitat in the northwest Pacific Ocean

  • Takuya FukuokaEmail author
  • Tomoko Narazaki
  • Chihiro Kinoshita
  • Katsufumi Sato
Original paper

Abstract

Green turtles in year-round neritic foraging habitats are widely considered to have small home ranges and to mainly feed on plant-based diets. In contrast, few studies have examined the summer-restricted habitats to which these turtles seasonally migrate. In this study, we investigated the foraging habits of green turtles migrating to the Sanriku Coast, a summer-restricted foraging habitat in a temperate area (38–39°N) of the northwest Pacific Ocean, using stable isotope analysis and biologging experiments from 2007 to 2015. Stable isotope analysis (n = 40, straight carapace length (SCL): 36.8–90.9 cm) indicated that most of the turtles, especially all smaller turtles (n = 35, SCL < 58 cm), relied on gelatinous prey before arriving at the Sanriku Coast. According to the biologging experiments (451.2 h of behavioral data and 43.2 h of video data, n = 6, SCL: 44.5–81.0 cm), the turtles shifted their main food to macro-algae (135 out of 148 feeding events) and consumed it at the sea bottom during their stay in the specific localized area of the Sanriku Coast. However, the turtles still consumed gelatinous prey in midwater during their movement to other locations along the Sanriku Coast and/or during their migration to southern overwintering habitats (13 events). These results indicated that green turtles migrating to the Sanriku Coast exhibit dietary diversity relative to year-round habitats, and the turtles in this area seem to consume gelatinous prey during the transit period in addition to feeding on macro-algae during the resident period.

Notes

Acknowledgements

We are grateful to all volunteers from the Fisheries Cooperative Association of Funakoshi Bay, Hirota Bay, Kamaishi Bay, Kamaishi-Tobu, Michishita, Miyako, Ofunato, Okirai, Omoe, Shin-Otsuchi, Ryori, Sanriku-Yamada, Sasaki, Toni, Yamaichi, and Yoshihama, who provided us with wild-caught sea turtles. Special thanks to M. Kurosawa, K. Morita, J. Takada, M. Hirano, T. Abe, T. Tashiro, I. Okaya, K. Takahashi and T. Kikuchi, for their great assistance in retrieving the data loggers. We also thank Y. Fujiwara, S. Takuma, H. Murasaki, K. Onitsuka, I. Nakamura, N. Miyata, S. Nobata, M. Yamane, T. Iwata, H. Nishizawa, and T. Abe who assisted in the field. We appreciate T. Miyajima and N. Saotome for their support with the stable isotope analysis. This study was performed under the Cooperative Program of Atmosphere and Ocean Research Institute, The University of Tokyo. We acknowledge the use of the Maptool (http://www.seaturtle.org/maptool/) program for mapping the study site and data logger retrieved sites. We thank three anonymous reviewers for their constructive comments and recommendations. Finally, we would like to dedicate our work to all the people in our study area who were severely affected by the tsunami on 11 March 2011.

Funding

This study was financially supported by the Tohoku Ecosystem-Associated Marine Sciences (TEAMS), the Bio-Logging Science, the University of Tokyo (UTBLS), a Japanese Society for the Promotion of Science (JSPS) research Grant (24241001 to KS), a JSPS Research Fellowship for Young Scientists (16J06542 to TF).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

This study was performed in accordance with the guidelines of the Animal Ethic Committee of the University of Tokyo, and the protocol of the study was approved by this committee (P12-13, P13-6, P14-3, and P15-7).

Supplementary material

227_2019_3481_MOESM1_ESM.pdf (128 kb)
Supplementary material 1 (PDF 127 kb)

Supplementary material 2 (MOV 5016 kb)

Supplementary material 3 (MOV 17539 kb)

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Takuya Fukuoka
    • 1
    • 2
    Email author
  • Tomoko Narazaki
    • 1
  • Chihiro Kinoshita
    • 1
  • Katsufumi Sato
    • 1
  1. 1.Atmosphere and Ocean Research InstituteThe University of TokyoKashiwaJapan
  2. 2.International Coastal Research CenterThe University of TokyoOtsuchiJapan

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