Sicily Fiennes investigates the fragile ecological state of Greek loggerhead turtles, and the efforts to conserve their population.
Written by: Sicily Bambini Fiennes
Loggerhead sea turtles have likely been nesting in Greece for many centuries, but they were first discovered there in 1977 by Dimitris Margaritoulis and Anna Kremezi-Margaritouli. The species Caretta caretta has now become synonymous with the country, notably nesting in the Peloponnese, Crete and Zakynthos. However, due to anthropomorphic activity, the Mediterranean subpopulation has? become part of a collection of 10 threatened loggerhead subpopulations worldwide, known as Regional Management Units (RMU’s). Combined, these subpopulations lay 200,000 clutches annually (Casale, P. & Tucker, A.D. 2015.). Their protection is especially important as they are a small yet integral part of just one sea turtle species. There are 7 species worldwide which all face varying anthropogenic threats to their survival.
The biggest threat to Mediterranean loggerhead sea turtles is commercial fishing, most notably bottom trawling and drifting longline fishing. This is compounded by human tourism. On the islands of Zakynthos and Crete, tourism has massively increased as they have become popular holiday destinations, particularly so in the resorts of Laganas and Rethymno.
The majority of loggerhead turtle nests in the Mediterranean are protected by a small non-government organisation (NGO) called ARCHELON (The Sea Turtle Protection Society of Greece). This year has been unparalleled in terms of nest numbers, and is proving to be one of the most successful ARCHELON has ever experienced. The year’s first nest was found on Gerakas on the 11th of May 2016 by the National Marine Park of Zakynthos, making it the earliest laid annual nest on record. Last September ARCHELON projects had 3,250 nests, and as of this year, there are over 5,106 in August alone! This is likely a result of the incredible effort to protect the nests by conservationist volunteers.
ARCHELON has protected sea turtles for over 35 years on Greek beaches. Collectively, volunteers walk over 75 km of beach each day in a gargantuan effort to protect sea turtle nests. ARCHELON’s work consists of morning and night surveys so scientists can assess turtle activity on the beaches, protecting the nests, and tagging the nesting females. Raising public awareness is also a major part of ARCHELON’s work; this include schemes such as information stations, presentations in hotels, turtle spotting tours and providing live information to beach users.
Why have nest numbers increased ?
Loggerheads and sea turtles all over the world are at risk from climate change, with their nests being particularly vulnerable. Sea turtles, along with other reptiles, are oviparous, meaning they lay eggs. The sex of their eggs is influenced by the temperature of the sand in which they incubate. There is already thought to be a strong bias towards female hatchlings, with one study in 2010 finding that 90% of loggerhead newborns were female (Casale, P. and Margaritoulis, D., 2010). With only a minor rise in mean nest temperature, the risk of complete feminisation of a nest is higher, which could drastically reduce the number of reproductive males (Casale, P. and Margaritoulis, D., 2010).
Increasing temperatures have a number of other effects: i they lead to faster development of egg clutches, which results in a shorter inter-nesting period in the water. They may also contribute to nests being laid earlier, possibly explaining the increased nest numbers. Global warming could also affect the embryonic development of the eggs and reduce hatchling emergence
In recent years Greece has experienced warmer winters, therefore raising the surface temperature of the sea, which might have triggered earlier nesting this year. Increased temperatures may also have affected food availability, which resulted in greater nutrients becoming available to nesting females, leading to an increased number of nests.
Rising sea temperatures also pose a risk. In several key nesting areas beds of seagrass, Posidonia spp., act as natural barriers to prevent erosion of nesting beaches. Rising sea levels could affect the deposition of such seagrass, therefore making these nesting beaches vulnerable to erosion. This can decrease the area of beach habitat which is available for sea turtles to use, as the soft sand at the back of the beach is preferred for nesting.
The protection of nests has proved to be particularly successful in the Peloponnese, in the south of the Greek mainland. Here metal grids are essential to protect the nests due to high rates of stray dog predation. These are placed over the nest and held in place by bamboo rods. Additionally, there is a high rate of nest relocations carried out by ARCHELON in the Peloponnese due to variable sea levels, which can change sand deposition levels and inundate nests if relocation measures are not taken. The spike in nest numbers in this area is likely due to these conservation measures, which ensure that the turtles have a better chance at development. The ramifications such a rise holds for ARCHELON are huge, as it confirms that the work it has been doing for the past 35 years is finally, clearly showing.
A lot can be learnt from Kyparissia’s ongoing success, both in terms of hatchling survival rates and attempts to infer the minimum sexual maturation age for loggerheads in the Mediterranean. Kyparissia Bay has now overtaken Zakynthos as the largest rookery in the Mediterranean with over 2500 nests, an unexpected increase of 175 % from last year. This increase has also helped scientists to understand when the first generation of protected hatchlings will come back as neophytes (‘new turtles’) to nest, which would confirm Casale’s predictions of minimum sexual maturity (Casale et al, 2011).
Students and young people are mobilised now more than ever to offer support to NGOs such as ARCHELON, especially those of us who study science. We can offer these skills where help is needed: every paper we write, or lecture we sit through, equips us with tools which can be applied to fieldwork and conservation. Volunteering is about being part of something bigger than yourself; it is about whatever contribution you can provide!