seaturtle.org : MTN : ARCHIVES : Sign In

Marine Turtle Newsletter 160:5-7, © 2020

Marine Turtle Newsletter-Online

A Juvenile Green Turtle Long Distance Migration in the Western Indian Ocean

Cheryl Sanchez1, Charles Lucas2, Ochieng’ Odhiambo2, Justin Beswick2 & Casper van de Geer3
1Seychelles Islands Foundation, PO Box 853, Victoria, Mahé, Seychelles (E-mail: aldabrascience@sif.sc)
2Local Ocean Conservation, Watamu, Kenya (E-mail: justin@localocean.co)
3Marine Turtle Research Group, Centre for Ecology and Conservation, University of Exeter, Penryn, UK (E-mail: c.vandegeer@exeter.ac.uk)

Juvenile sea turtles are known to undertake long migrations (Hays & Scott 2013) and undergo ontogenetic shifts in their foraging habitats (Bolten 2003; Reich et al. 2007; Arthur et al. 2008). Juveniles can remain in the same habitats for many years (Bressette et al. 1998; Ehrhart et al. 2007; Redfoot & Ehrhart 2013; Shimada et al. 2014), providing an opportunity for in-water studies of marked individuals. Due to the recapture of tagged turtles, a picture is emerging of the migratory patterns between Kenya and the Seychelles (Zanre 2005; von Brandis et al. 2017). Whereas previously described migrations have all taken place from the Seychelles to the continental African coast, the migration presented here is the first documented case of a juvenile green turtle in the opposite direction.

On 3 November 2015, a juvenile green turtle (Chelonia mydas) was captured in the early morning in a net by Baraka Omar, a local fisher, near Watamu, Kenya (Fig. 1). Omar notified Kenya-based NGO Local Ocean Conservation (LOC), and their Bycatch Release Program (BCRP) team met him at the landing site. LOC has been running the BCRP in collaboration with Kenya Wildlife Services since 1998 and works with hundreds of fishers, conducting nearly 1,400 rescues per year. Upon collection of the turtle, it was assessed and found to be in good health and “generally clean,” meaning it was free of algae and epibionts. Measurements of the turtle were taken as per Bolten (1999): minimum curved carapace length (CCLmin): 38.8 cm; curved carapace width (CCW): 38.4 cm; weight: 7.4 kg. Photos of the left, right and top of the head were taken for future visual identification purposes (Fig. 2). As per LOC protocol, this juvenile turtle was tagged in the left rear flipper (KES0113; Inconel 681 tag from the National Band and Tag Company, Kentucky, USA). Since the start of the BCRP, over 8,100 turtles have been tagged by LOC, most of which have prefix KE, KES or KEL. The tagged turtle was then transported to the beach in the Watamu Marine National Park the same day and released.


Figure 1. Map showing the original capture location of the juvenile green turtle at Watamu, (Kenya) and the recapture location of Aldabra (Seychelles) nearly four years later.

Four years later, on 19 September 2019, the same turtle was captured by research staff from the Seychelles Islands Foundation (SIF) Public Trust in the lagoon of Aldabra Atoll (Fig. 1, 2), Seychelles, nearly 950 km (straight line distance) from Watamu. Aldabra Atoll is a raised coral atoll and UNESCO World Heritage Site managed by SIF, about 1,100 km from the Seychelles main island of Mahé, and is nearly 400 km from Madagascar. The atoll consists of four main coralline islands, which surround a shallow interior lagoon (226 km2). A small team (typically 10-15 people) of permanent SIF staff live at a research station at the atoll for research and conservation purposes. The Aldabra in-water turtle monitoring program began in 1986, prior to SIF management, and has been part of routine monitoring predominantly in the lagoon since 1996. The turtle was caught during one of these in-water sessions and measured (CCLmin: 54.0 cm, CCW: 52.5 cm, weight: 45.5 kg). The left rear flipper tag was recorded and the turtle was tagged in the left and right front flippers (Inconel 681 tags: E4955, E4944) based on the SIF turtle tagging protocol. In the nearly four years between captures, the turtle grew 15.2 cm in length, 14.1 cm in width, and gained 38.1 kg, a growth rate of almost 10 kg and just over 4 cm in length per year.




Figure 2. Juvenile green turtle KES0113 at time of capture in Watamu, Kenya (top, middle), and KES0113 recaptured on Aldabra, Seychelles (bottom) nearly four years later.

Although adult green turtles have previously been found to transit between the Seychelles and Kenya (Zanre 2005; SIF unpublished data), this is the first account of a juvenile green turtle carrying out this migration. It is also the first time that a juvenile turtle has been found to swim from the continental coast to the Seychelles. A juvenile hawksbill turtle (Eretmochelys imbricata) carried out a similar long distance migration from the St. Joseph Atoll, Seychelles, to Kenya (von Brandis et al. 2017). This turtle was also captured by a fisher who reported it to LOC through the BCRP. Evidence of migrations to other continental African countries include the recovery of a tag from a green turtle which originated in the Seychelles on the Tanzanian coast (Sea Sense 2015) and a hawksbill turtle originally tagged in the Seychelles was found in Mozambique in the 1990s (J.A. Mortimer, pers. comm.). The recapture event reported here, combined with similar events in the region, highlight the connectivity of turtle populations the Western Indian Ocean (WIO) and the value of these tagging programs.

The work of LOC with local fishers has enabled the tagging of the reported juvenile green turtle, as well as the tag recovery from a hawksbill turtle (von Brandis et al. 2017) from the Seychelles. In this case, the juvenile green turtle was successfully released in Kenya and was then recaptured in a well-protected habitat at Aldabra. The use of both habitats, one with high human impact and the other with little human interference, highlights some of the risks and benefits these individuals may face. This recapture event underlines the wide geographic area that juvenile turtles potentially utilize and therefore the high levels of threat that they face during these migrations, such as bycatch and targeted illegal take (Bourjea et al. 2008). The tagging programs described here are contributing to the ability to effectively manage sea turtle populations in the WIO by providing insight into the migratory patterns of juvenile turtles. Stronger international collaboration between the various sea turtle conservation efforts in the region, exemplified by this paper, are vital to further deciphering connectivity of the turtle populations.

Acknowledgements. The authors thank Mr. Omar, who was active in Local Ocean Conservation’s (LOC) Bycatch and Release Program, from Nov 2014 to Oct 2016, and all the fishers who participate in the program. Thanks to Fikiri Kiponda who leads the Bycatch Release Program. LOC also acknowledge the continued support of the Kenya Wildlife Service of its conservation and outreach efforts. Thanks also to Seychelles Islands Foundation staff Jilani Suleman, Ronny Marie and Jessica Moumou for catching the turtle at Aldabra and to Nancy Bunbury for reviewing the draft manuscript. Thanks to Matt Carter for helping with the map.

ARTHUR, K.E., M.C. BOYLE & C.J. LIMPUS. 2008. Ontogenetic changes in diet and habitat use in green sea turtle (Chelonia mydas) life history. Marine Ecological Progress Series 362: 303-311.

BOLTEN, A.B. 1999. Techniques for measuring sea turtles. In: Eckert, K.L., K.A. Bjorndal, F.A. Abreu-Grobois & M. Donnelly (Eds.) Research and Management Techniques for the Conservation of Sea Turtles. IUCN/SSC Marine Turtle Specialist Group, Publication 4. pp. 110-114.

BOLTEN, A.B. 2003. Variation in sea turtle life history patterns: neritic versus oceanic developmental stages. In: Lutz, P.L., J.A. Musick & J. Wyneken (Eds.). Biology of Sea Turtles. Volume 2. CRC Press, Boca Raton, Florida. pp. 243-257.

BOURJEA, J., R. NEL, N.S. JIDDAWI, M.S. KOONJUL & G. BIANCHI. 2008. Sea turtle bycatch in the West Indian Ocean: Review, recommendations and research priorities. Western Indian Ocean Journal of Marine Science 7: 137-150.

BRESETTE, M., J. GORHAM & B. PEERY. 1998. Site fidelity and size frequencies of juvenile green turtles (Chelonia mydas) utilizing near shore reefs in St. Lucie County, Florida. Marine Turtle Newsletter 82:5-7.

EHRHART, L.M., W.E. REDFOOT & D.A. BAGLEY. 2007. Marine turtles of the central region of the Indian River Lagoon System, Florida. Florida Scientist 70: 415-434.

HAYS, G.C. & R. SCOTT. 2013. Global patterns for upper ceilings on migration distance in sea turtles and comparisons with fish, birds and mammals. Functional Ecology 27: 748-756.

REDFOOT, W.E. & L.M. EHRHART. 2013. Trends in size class distribution, recaptures, and abundance of juvenile green turtles (Chelonia mydas) utilizing a rock riprap lined embayment at Port Canaveral, Florida, USA, as developmental habitat. Chelonian Conservation & Biology 12: 252-261.

REICH, K.J., K.A. BJORNDAL & A.B. BOLTEN. 2007. The ‘lost years’ of green turtles: using stable isotopes to study cryptic life stages. Biology Letters 3: 712-714.

SEA SENSE. 2015. Sea Sense Annual Report 2015. Sea Sense, Dar es Salaam, Tanzania. 24pp. http://seasense.or.tz/reports-publications.

SHIMADA, T., S. AOKI, K. KAMEDA, J. HAZEL, K. REICH & N. KAMEZAKI. 2014. Site fidelity, ontogenetic shift and diet composition of green turtles (Chelonia mydas) in Japan inferred from stable isotope analysis. Endangered Species Research 25: 151-164.

VON BRANDIS, R.G., J.A. MORTIMER, C. VAN DE GEER & J.S.E. LEA. 2017. A long migratory record for a small post-pelagic hawksbill. Marine Turtle Newsletter 152:13-15.

ZANRE, R. 2005. Report on Watamu Turtle Watch’s Sea Turtle Bycatch Release Programme, Watamu, Kenya. Local Ocean Conservation, Watamu, Kenya. 95pp.