This March there was an unfortunate event on Western Beach. During the early hours, a dead Loggerhead Turtle, Caretta caretta, washed up and was found in a very poor condition. Its front right flipper was missing and the state of decomposition suggested that it had been dead for some time before washing up. On the upside, there was no direct evidence to confirm that the death was human induced although, anecdotally, it is possible that the loss of the front fin was due to some entrapment with fishing gear or an unlucky encounter with a passing boat.
Turtles form part of the reptilian family Cheloniidae, and the members are typically large marine animals. Over evolutionary time, their limbs have formed into fins and spend the majority of their lives at sea. The only remaining clue of their terrestrial heritage is that they lay their eggs on land and they even return to the very beach they hatched from. Their ‘shells’ are in fact a modified rib cage. The ribs have flattened out and fused together creating recognisable plates called scutes. Each separate species can be identified through the number and arrangement of the scutes.
The Loggerhead Turtle is a very popular example of one of these animals and has often appeared in animated films like ‘Finding Nemo’, portrayed as the ‘hip’ surfer type. Don’t be completely dismissive of this though as there is more truth to this stereotype than might first meet the eye. As the second largest marine turtle, loggerheads are oceanic dwellers and can be found within most of the major water bodies around the planet. They can cover huge distances whilst in the oceanic currents and research suggests that they use them in a similar way to the film.
In spite of this huge habitat, their status is set as vulnerable by the International Union for the Conservation of Nature (IUCN) for a number of reasons. Loggerhead turtles can take over 20 years before they become sexually mature. They are very slow to reproduce also as once they have laid around four clutches loggerheads take a break of between 3-4 years before they become sexually active again. This, added to the fact they rely of a high fecundity low survival rate means that populations can take a long time to recover.
Like all turtles, loggerheads return to beaches to lay their eggs from May until around August. The arduous crawl up the beach is very energy-intensive and once at the correct spot they have to dig deep before the nest is ready. Each clutch contains around 100 eggs. A lesser known fact is that the eggs within each clutch are fertilised from multiple fathers and this might be one of the keys to their success by ensuring genetic diversity. Loggerheads, as with many reptiles, have temperature-dependant sex determination with males being born if the average nest temperature is below 28oC and female born if above 31oC. Typically, the female digs just enough for the nest to span both temperature ranges which ensures both sexes are born.
Ultimately, environmental factors can have a huge effect of the sex ratio and this is evidenced in multiple scientific papers spanning many years of research. A major concern is that as the planet warms in line with climate-change predictions, that the male: female ratio will tip ever more in favour of females, until the point where there are no more males. Obviously, this would be catastrophic for the reproduction potential of the standing population of loggerheads all over the world. Much work is already being done by Turtle sanctuaries to remove eggs from nests and artificially incubate them to increase the number of males. These are then released back into the wild as soon as they are hatched.
Another interesting climate-change anecdote is the fact that as average sea temperatures are rising so are jellyfish numbers. Jellyfish are also turtles favourite food. Typically, when prey numbers increase, the predator numbers follow suit albeit with a slight lag. Presently, we are seeing turtle numbers decline whilst jellyfish numbers are increasing. This means there are two factors pushing up jellyfish populations. This is a major reason for the increased jellyfish numbers we are seeing locally on our beaches every summer. An obvious natural solution to this would be to reduce shipping and protect all turtles. In turn, they would consume standing jellyfish stocks and come the bathing season we would not be stung, so often.
Twenty-five years ago, turtle numbers in the bay were much higher than they are today with anecdotal evidence suggesting they were common sighting when out at sea. Today, an encounter is an exceptionally rare occurrence, giving testimony to the general decline in our marine environment. With a predictable increase in shipping within the Straits of Gibraltar, and the bay itself, the outlook remains bleak. The washed-up carcass of the Loggerhead demonstrates that they are still out there, for now.