Argostoli Bay is a picturesque bay and harbour on the western coast of Kefalonia, Greece. Tourists flock here to enjoy the crystal turquoise waters, sun-drenched beaches and Mediterranean food, but another attraction has become a highlight
of the island: turtles. However, recent feeding habits are having damaging effects on the behaviour of this usually docile species.
The Loggerhead turtle (Caretta caretta) is the most common turtle species throughout the Mediterranean, commonly found nesting on beaches across Greece, Turkey and the northern coasts of Africa. Their natural diet consists mainly of
shellfish, including sea urchins and clams, which require strong jaws and a powerful bite, enabling them to crush through the thick shells of their prey.
Despite the common occurrence of Loggerheads across beaches, the species is listed as vulnerable, threatened by pollution, entanglement in fishing gear and habitat loss, as beaches continue to be developed for tourism. These turtles are an
important species in the Mediterranean marine ecosystem, controlling populations of sea urchins that may otherwise damage, and potentially decimate, seagrass meadows and local reefs.
Through feeding on shellfish, minerals and nutrients are recycled, balancing the sediments on the seabed and returning important calcium powders to the water, making the Loggerhead a keystone species in the local ecosystem. Their shell also
provides a mobile micro-habitat, with a record number of over 100 different species of plants and animals found thriving on a single turtle’s back.
Loggerhead turtles are a migratory species, spending the majority of their time at sea, only coming ashore to mate and lay eggs in the summer months. However, recent observations in Greece have found that many turtles are remaining at the
coastline, no longer migrating into the Adriatic sea to forage over winter.
‘Over 100 different species of plants and animals found thriving on a single turtle’s back.’
In Argostoli Bay, Loggerheads can be commonly seen fringing the harbour walls year-round. Wildlife Sense, a turtle research and conservation organization, has been monitoring turtle populations on Kefalonia and has found worrying results.
Loggerhead turtles have become habituated and remain in Argostoli Bay year-round, despite human disturbances, such as marine traffic, fishing and tourism.
They have been regularly observed feeding on fishing bycatch and food thrown into the water by tourists, such as bread, chips and other non-natural items. It is thought that this is attracting more and more turtles to remain in the harbour
all year, as it offers a constant and easy food supply. These foods can cause nutritional deficiencies in the turtles, alongside other health complications such as cardiovascular disease.
Fishermen also feed bycatch to the turtles to attract an increasing number of tourists to the area, which maximises their chance of selling the morning catch, but causes further damage to the local marine ecosystem. Loggerhead turtles are
naturally solitary animals, however they are becoming increasingly concentrated in Argostoli Bay, which is having adverse effects on their behaviour.
A study conducted by a team of researchers at Wildlife Sense found that antagonistic social interactions between turtles increased in areas where turtles were fed fish by tourists and fishermen. They observed increased aggression between
individuals, displaying behaviours such as chasing, sparring and biting. It was found that the most common aggression occurred between individuals feeding on bycatch, highlighting its detrimental effect.
It has also become clear that the resident turtles have become accustomed to boat traffic and humans in the bay; this poses a further threat to their population as it increases the chance of damage by marine vehicles and illegal hunting.
The turtles learn to associate boats with food, and are abandoning natural foraging and hunting behaviours to follow harbour traffic.
The accumulation and permanent residence of turtles in the bay means a continually decreasing number of individuals are foraging at sea, and consequently less calcium is being powdered and returned to the sediments. Turtles are omnivorous
and also feed on jellyfish, helping to control populations of jellies that are rapidly increasing with the global decrease in fish stocks.
‘The accumulation of turtles in the bay means a continually decreasing number of individuals are foraging at sea.’
The turtles also sift through the surface sediment layers when searching for crustacean and mollusc prey, causing aeration which helps provide oxygen to burrowing organisms and prevents anoxic pockets (areas depleted of oxygen) forming.
This affects the rest of the ecosystem, as these key roles are no longer being fulfilled to their previous levels, which can upset the natural cycles and processes that are vital in the functioning of a healthy marine ecosystem.
To combat the detrimental effects of feeding on Loggerhead turtle behaviour, it is important that locals, fisherman and tourists are educated about the impact of their actions. Local guidelines state that feeding is prohibited, however
stricter reinforcement is needed to have a significant effect.
Suitable natural foraging grounds are becoming increasingly rare with the expansion of shipping routes and increased marine traffic within the Mediterranean, meaning Loggerheads are likely to be forced to congregate and interact more
frequently than they are naturally used to.
All these actions exacerbate the problem of the turtles becoming dependent on humans for food. This is an unhealthy relationship and one which should not be encouraged, as individuals become territorial and display increasingly aggressive
behaviour, harming both the individual and the population as a whole.
Featured Image: Lewis Burnett | Ocean Image Bank
Comis C., Vallianos N. and Betts J. (2022) Feeding loggerhead sea turtles increased their social antagonistic interactions in Kefalonia, Greece. Wildlife Sense.