Research on loggerhead behaviour and movement patterns

By Gail Schofield

Since 2003, I have spent many hours in the sea between April and July collecting information by snorkelling on the in-water behaviour of loggerhead sea turtles (Caretta caretta) which frequent Laganas Bay on the island of Zakynthos to breed.

Gail conducting in-water snorkel surveys

There are 3 existing marine protection zones which were designated prior to the formation of the National Marine Park of Zakynthos (formed 1999) in Greece, based on nesting beach information. Hence the actual marine area use and behaviour by the largest loggerhead breeding population in the Mediterranean was unknown. I documented a wide range of behaviours being exhibited by both male and female loggerheads and movement patterns when in the marine breeding area, and compiled a list of possible research ideas which I combined into a proposal for a PhD study.

Documented behaviours included fish cleaning; mate searching; foraging

(for more details see Schofield et al. 2007. Marine Ecology Progress Series. 336: 267-274

In 2006, I  initiated a PhD study (Universities of Ioannina, Thessaloniki & Patras and the University of Wales-Swansea in collaboration with the National Marine Park of Zakynthos) to investigate loggerhead sea turtle movement and behaviour in the marine area of the National Marine Park of Zakynthos. Understanding movement patterns and the factors that affect animal distribution are integral components of conservation and natural resource management. This is particularly true of the NMPZ marine area where sustainable business endorsement schemes are in development.

I studied the in-water movement of female loggerheads using TrackTag© GPS loggers placed on 3 female loggerheads in 2006, 4 in 2007 and a further 9 in 2008 (ongoing) attached in May and retrieved in June of each year. The data indicated that female turtles primarily use a 5 km stretch of nearshore waters at seabed depth of 1-5 metres. This study clearly showed that the level of protection provided by the 3 existing marine zones required updating. Hence the NMPZ introduced a designated ‘Ecotourism Zone’ in which only boats endorsed by the NMPZ may enter and operate (for more details see Schofield et al. 2007. Journal of Experimental Marine Biology & Ecology 347: 58-68)

Female loggerhead sea turtle following TrackTag GPS logger attachment

While the GPS tracking study provided new insights into female loggerhead movement, information about area use by male loggerheads was required to determine how  to update existing protection measures. We used “Fastloc™” GPS transmitters so that we could follow the movements of male loggerhead sea turtles to obtain information on:

  1. If area use overlapped with females in the protected marine area
  2. Period of residency by males
  3. Migratory routes and whether males use similar wintering/foraging grouds to the females in other parts of the Mediterranean.

All male and female turtles were captured using the established ‘rodeo’ technique, and units were attached to their carapaces. Preliminary data from the 2008 season will be made available as soon as possible.

Capture of loggerhead resting in shallow water

Transmitter attachment by Gail following capture of male loggerhead

Male turtle about to be released with transmitter

Male loggerhead sea turtle following Sirtrack GPS transmitter attachment



2008 GPS transmitter attachments to male loggerhead turtles

Fastloc GPS transmitters were attached to three male turtles on the 3rd and 4th of May 2008 on the Greek island of Zakynthos. The units began operating from the first day and transmit 1-16 locations accurate to within 40 metres each day. Two of the males left the breeding area on the 17th and 18th of May and migrated to wintering/foraging grounds in northern Greece and Croatia. The male at Croatia has started moving south and is currently at the foot of Italy. One male remained on Zakynthos and appears to be a resident male, which is the first scientific confirmation that resident loggerheads exist on Zakynthos ! There is anecdotal information from fishermen that a second male ‘Sotiris’ frequents Agios Sostis port throughout the year. We do not know for how long the transmitters will continue operating – as it will be interesting to see if the three males return to breed in 2009. Full results will be published during 2009. Preliminary results appear below.



John D. Pantis - Aristotle University of Thessaloniki, Greece

Panayotis Dimopoulos - University of Ioannina, Greece

Graeme C. Hays – Swansea University, UK



                                                Boyd Lyon Sea Turtle Fund Scholarship & The Ocean Foundation

                                                The British Chelonia Group                                                       

                                                The Peoples Trust for Endangered Species

                                                TrackTag©  -  Peter Brown

                                                The Bangor University - Charles M. Bishop

                                                The National Marine Park of Zakynthos

                                                Swansea University

                                                University of Ioannina


Sea turtle in-water capture team and boat drivers: Martyn Baker, Kostas Gou\nelis, Giannis Liveris, Giorgos Livanis,, Kostas Katselidis, Martin K.S. Lilley, Nikos Margaris, Giorgos Mitrouskas, David Oakley, Mike-Jen-Hannah Sheldon

Sea turtle in-water & beach retrieval assistants: NMPZ personnel: Sofia Alexiou, Sakis Botos, TyAnn Lee, Ines Palomares, Veneranda Petta-Bika, Enrico Marcon; Archelon volunteers: Mark Barrett, Philip Bradshaw, Chris Dean, Bronwen Gill, Alex Hogg, David Oakely, Emma Ransome, Bianca van Divendyk, Nick Walters, Judith Zbinden

Special thanks to V. Hobson, L. Sourbes, K. Papadimitriou and D.G. Schofield with GIS assistance and advice


Page last updated:  15 December 2008