Photo ID in the Harbour of Argostoli

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Green Sea turtle

The harbour of Argostoli encompasses a large seagrass meadow which is used yearly by many turtles as a foraging, resting, and mating ground. Within the harbour we encounter two species of sea turtles; the most numerous and regularly seen loggerhead sea turtle (Caretta caretta) and the rare green sea turtle (Chelonia mydas).

2021-01-29 Atlas 2012 Photo id loggerhead

In most cases, any greens recorded in the harbour are juveniles with an approximate age between 1 and 5 years. It has to be noted that Kefalonia is not a nesting site for the green sea turtle, which in the Mediterranean mainly nests in Turkey and Cyprus. Therefore, these juveniles must travel great distances after hatching to enter our harbour. The loggerheads we record within the harbour vary largely in size and consequently, age. These, however, are mostly a lot larger and older than the greens seen.

2021-01-29 Atlas 2020 Photo id loggerhead

Every summer we run a photo identification project in the harbour. Photo ID is a well-known and widely used technique that uses natural markings to identify individuals. A sea turtle’s head consists of scutes that have unique shapes and patterns on each individual turtle, much like a human fingerprint. By photographing a turtle’s head and comparing it to photos of turtles from previous years we are able to deduce which individuals return to the harbour every year, the sex ratio, and even how long turtles tend to stay in our harbour.

Over the years we have noticed an increasing trend in the number of turtles in the harbour. 2020 was an exception, a possible explanation may be reduced sampling of the harbour due to COVID-19 restrictions. Alternatively, 2020 had lower nesting numbers than 2019 which may explain the lower number of turtles in the harbour. This year is the first time we are running this project throughout the winter months which is giving us some really cool information. So far we have been able to identify 17 turtles in 2021! We are hopeful that through sampling all year round we will record a record number of turtles and reveal some interesting trends such as when most turtles return from their winter foraging grounds.

Written by josh Witzmann

Tags: Chelonia mydas, green turtle, research, Caretta caretta, sea turtle


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