The Turtle Project

Loggerhead sea turtles in Kefalonia

 

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Introduction
Nesting sites
Some general and nesting numbers
Location and sex ratio
Permanent population

Introduction

turtle tracksThe Loggerhead sea turtle, Caretta caretta nests on most of the southern sandy beaches of Kefalonia. Many of these beaches have been untouched by human development until recently, and therefore offered turtles a safe place to nest, secluded from the outside world. However, in the past 20 years tourist development has been encroaching into these untouched nesting habitats.

Nesting sites

We monitor the population of Loggerhead sea turtles on the main nesting site of Kefalonia, Mounda beach. This beach has been monitored for more than 20 years by different organisations. The number of nests here has shown signs of decline.
We are also making an effort to monitor other nesting beaches, to assess the general situation of the island population. We need some more resources to do this properly.

loggerhead turtleSome general and nesting numbers

Loggerhead sea turtles in Kefalonia are very similar to their fellows in the Mediterranean, which in turn are a little different from oceanic Loggerheads, in that they are smaller. A brief list of their features (all quantities are approximations of averages):

- adult female length: little less than 1 m
- hatchling at birth length: 5 cm
- adult female weight: up to 100 kg
- hatchling at birth weight: less than 20 g
- sexual maturity minimum age: probably 20 years
- number of eggs in a nest: little more than 100
- proportion of infertile eggs in each nest: 5-20%
- number of nests laid in a season by one turtle: 2-3
- years between nesting for a turtle: 2-3
- nesting season: end of May - beginning of August
- hatchling season: end of July - beginning of October
- incubation period: 55 days
turtle nest- nest depth: 20-40 cm

Location and sex ratio

Kefalonian Loggerhead sea turtles are remarkable in various ways.
The island is one of the northernmost nesting sites of sea turtles in the world. This might have important implications in the sex ratio of offspring produced on the island. Temperatures during incubation determine the sex of sea turtles, in a process called Temperature-dependant Sex Determination. Higher temperatures produce more females. Many studies agree on assigning a female skewness to Mediterranean sea turtle populations. Therefore, nesting sites with lower temperatures produce more males and can be considered male reserves. They acquire even further importance in view of global warming. It makes sense to hypothesize that the latitude of Kefalonia produces lower temperatures on its nesting beaches and therefore more males, although this has not been investigated.

argostoli lagoonPermanent population

Kefalonia is also unique in hosting a resident population of Loggerhead sea turtles. There is evidence that a small population of turtles spend the winter in Koutavos lagoon near Argostoli (see picture right). This is an exception for a highly migratory species like Caretta caretta, in the highly migratory group of sea turtles.