A Sea Turtle Story
It is late August in Argostoli on the Greek island of Kefalonia. Peak holiday season is in full swing and walking along the harbourside there is a buzz in the air. Large groups of tourists are gathered along the waters edge. Dozens of fishing vessels are moored alongside the harbour, attempting to entice the onlookers to the day's catch. Upon closer inspection it is not the fish the tourists are interested in, but rather the creatures that are swimming alongside the boats in the azure blue waters of the Mediterranean.
As the large red-brown patterned carapace glides into view it is clear that what has caught the tourists’ attention are the majestic Loggerhead sea turtles this historic harbour is famous for.
The turtles glide gracefully through the water as if flying, only stopping to feed on the barnacles living on the harbour wall, or the by catch from fishermen.
I am amazed by their size; on average 100cm in length and weighing more than 135kg they are heavier than most humans. It is an astonishing transformation from the small and vulnerable hatchlings that can fit in the palm of a hand.
Loggerheads are the world’s third largest turtles, after the soft-shelled Leatherbacks and the hard shelled Green turtles. They are characterized by their uniquely large head and reddish brown shell and are omnivorous, feeding mostly on bottom dwelling invertebrates.
Loggerhead turtles have been a feature of the world’s ecosystems for the last 40 million years, and although their range covers all but the most hostile of the world’s oceans they are now on the IUCN list of vulnerable species. The natural obstacles faced by young and adult sea turtles are staggering, but it is the increased threats caused by humans that are driving the species to extinction.
This is the story of the Sea Turtles of Kefalonia, of the epic journey from egg to adult, and the challenges faced along the way. Challenges which only the fittest and luckiest individuals will survive and return to Kefalonia to produce the next generation.
These adults in the harbour are the lucky few. Only an estimated 1 in 10,000 overcome all the obstacles to survive to this stage.
The Greek islands are an important area for the turtles, which feed in the inshore waters, and lay nests on the sandy beaches that line the coast.
I travelled to the island of Kefalonia to document the challenges loggerhead turtles face on their journey from egg to adulthood, and find out how conservation organizations are working to save the species from extinction.
I joined the charity Wildlife Sense in August to investigate the threats facing the sea turtles in Kefalonia, and find out how volunteers are helping protect the species.
The first stage in the life of a Loggerhead sea turtle occurs when the female leaves the sea and climbs up the beach to build a nest and lay eggs. Our first job was to survey the beaches for any evidence of nesting.
Rising at 5am each morning with the stars still shining and the sun below the horizon, I joined other volunteers as we cycled for over an hour to reach the nesting beaches. Walking along the beaches, we looked for evidence of any new emergences before tracks were washed away.
A fascinating characteristic of sea turtles is that they almost always return to the same area of their birth, and commonly the same beach, to lay their own nests.
Adult females use the cover of darkness to emerge from the sea and climb the beach to construct a nest and lay eggs. This is the only time an adult will leave the sea during it’s whole life cycle, up to 70 years.
If a female emerges and decides a beach is unsuitable for nesting she will not lay eggs and return to the ocean. These types of non nesting emergences are becoming increasingly common due to factors such as tourist disturbance and light pollution from hotels and beach bars.
These morning surveys also monitor existing nests for any evidence of hatchlings. By counting tracks and monitoring nests each day valuable data can be collected. Nests contain on average 100 eggs and incubate for 50-60 days. As we know when each nest was laid, we can estimate when each nest will hatch. If a nest is 10 days overdue, at the 70 day mark, then a nest must be excavated to find the cause of hatching failure.
This was my next task with the Wildlife Sense team.
There are many reasons why a nest may not hatch. Disturbance by tourists, predators and the sea or bacterial / fungal infection could all be responsible.
On our hands and knees we dug down to find the nest, often buried over 30cm below the surface, creating a crater like hole on the beach in the process. As we dug down we came across a large rock. Our fear was the rock may have blocked the exit of he hatchlings from the nest below. As we removed the rock sure enough we caught our first glimpse of the nest, and the palm sized outline of a hatchling. It was motionless, and upon closer inspection had clearly been dead for some time.
We dug on, encouraged by the thought there may still be live hatchlings in the nest below. Moments later we were rewarded with movement of two live hatchlings stuck beneath the rock. We carefully proceeded to lift them up and place them in the trench we had dug towards the ocean. The first stage of a hatchlings life requires a weary scurry to the sea, warming muscles up before battling the elements of the ocean.
Unfortunately these were the only remaining live individuals and we set about cracking the unhatched eggs open to investigate the reason for their failure to hatch.
It appeared bacterial and fungal infections had overcome a number of eggs, specifically from the microbe S. marcescens, which is characterized by an almost fluorescent pink coloring to the yolk. These turtles had fallen at the first hurdle of their epic journey.
The next day brought more drama. During the routine morning beach survey we found that the storm the previous night had caused the tide to rise, flooding a number of nests. With no intervention the wet eggs would rot, so we were left with no choice but to relocate the nest. It was a race against time, and involved carefully removing all the eggs from the flooded nest and relocating them to a more suitable area as soon as possible. For one nest it was too late, and the tide had risen too high. The eggs had turned a green shade and started to rot, the result of hours submerged in a lake of saltwater. Two more nests, although briefly submerged by the tide, were slightly higher up the beach and luckily had not been submerged long enough to be destroyed. We successfully relocated these nests to dry sand higher up the beach where they would develop as normal.
Without the work of the volunteers around the Argostoli area 4 nests would have been lost to the storm that night.
If eggs are successful in hatching then the young turtles will encounter a new set of challenges in their first stage of life, on their journey from nest to sea.
Light pollution is a significant problem for hatchlings. Through millions of years of evolution turtles have adapted to hatch at night, when the sand is coolest, and follow the brightest light, historically being towards the sea due to the reflection of the night sky in the water. Because of lights from beach bars, hotels and cafes, hatchlings have trouble determining which direction to head in. Hatchlings head towards these bright lights rather than the ocean and once the sun rises and temperatures climb, the newborns are at significant risk of dehydration.
To combat this problem volunteers from Wildlife Sense spend nights on the beaches most affected by light pollution. Boxes are placed over the nests to prevent hatchlings heading towards artificial lights. Volunteers regularly check the boxes and place any hatchlings in a trench to begin their journey. This stage really highlights the vulnerability of the hatchlings. After following tracks to find a hatchling heading away from sea towards the bright lights of the beach bar I held the 20g baby in the palm of my hand. It is remarkable that in 20 years these babies may return to Argostoli harbor weighing more than most humans.
Once the hatchlings disappear beyond the waves the real struggle for survival begins. A tiny speck in a vast ocean, young turtles are prey for a number of oceanic predators, including crabs, sharks and whales.
It will be at least 17 years until the females will return to land to lay eggs. Hatchlings swim for 20 hours until they are far out to sea, where they live using the macroalgae Sargassum for protection. They will remain here, growing until they are 45cm in length at juvenile age, where they will then migrate to inshore waters using a combination of magnetic and visual cues to direct themselves.
Returning to inshore waters, adult turtles again face a range of threats from contact with humans.
Although poaching is not a problem in Europe, in central America turtles are seriously threatened by hunting for their eggs and meat, which are considered a delicacy in many places.
In Europe the primary threat to adult turtles is entanglement in fishing gear including longlines and gillnets. Loggerheads need to breath air at least every 7 hours, so getting caught in fishing nets is extremely dangerous and can often result in drowning.
It is worrying that the harbor turtles of Argostoli are in such close proximity to fishing vessels and the associated dangers they present. The slow moving giants are often unable to react to fast boats, resulting in serious injury following collision.
In addition to the commercial fishing vessels in the harbour individuals fish with hooks and lines from the harbour wall. Although illegal, the harbour authorities do little to enforce the law, despite the volunteers best efforts for cooperation.
Plastics also pose a threat to sea turtles, as they are often mistaken for food items. A common example is the ingestion of plastic bags, easily mistaken for the jellyfish that make up a large part of the sea turtle diet. Ingested plastic causes numerous health concerns, including intestinal blockage, reduced nutrient absorption and malnutrition, suffocation, ulcerations, or starvation.
Ingested plastics release toxic compounds, including polychlorinated biphenyls, which may accumulate in internal tissues. Such toxins may lead to a thinning of eggshells, tissue damage, or deviation from natural behaviors.
There were worrying levels of plastic debris found every morning both on the beach surveys in areas yards from nests, and also numerous items floating in the harbour, tempting the turtles to a fatal meal.
Finally, climate change poses a threat to the species as a whole. An intriguing feature of turtle offspring is that sex is determined by the ambient temperature of the nest. An incubation temperature of 3 degrees celsius results in an even sex ratio. If the temperature is lower, more males will be born, and if higher, more females will develop. As global temperatures increase scientists predict sex ratios will skew and the number of females will increase. This raises concern over the connection between rapid global temperature changes and the possibility of long term population extinction.
As the threats to the species only appear to be increasing it is encouraging that commitment from conservation organizations, volunteers and local communities appears to be growing. Valuable data is being gathered, nests are being protected and local communities and businesses are engaging in the conservation effort by switching off beach bar lights and reducing pollution. Fishermen are using more sustainable methods, with the introduction of turtle excluder devices in nets enabling turtles to escape if caught in gillnets.
For the species to survive in the long term cooperation between conservationists, fishermen and the tourist industry is key. Fishermen and their equipment are the primary cause of non-natural adult deaths, and many nesting beaches are shared with tourists and beach bars. If these groups can work together then there are at least a few less challenges for the Sea turtles on their journey through life and one day, maybe the lost hatchling I held in my palm will return to the island to lay its own nest.
