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Sea turtles - at ‘loggerheads’ with global warming

Ensuring maximum protection for a loggerhead turtle's 79 eggs has got us thinking of protection, but what are the major threats affecting turtles?

Duncan Barry
4 July 2012, 12:00am
The loggerhead is the most abundant sea turtle in the Mediterranean Sea, and the US.
The Malta Environment and Planning Authority last week issued instructions to ensure maximum protection for the site where a turtle laid 79 eggs earlier in the week. As things stand, Ġnejna Bay is now out of bounds for barbeques, music, pets and any deep holes dug in the sand by swimmers have to be filled in before they leave.

The emergency conservation order prohibits various activities and is valid for six months.

This order was released after a surprise visit by a Loggerhead Sea Turtle that crawled on to the beach recently, dug a hole and laid 79 eggs, which left those who witnessed this rare scene astonished.

According to MEPA, loggerhead turtles were protected by national and international legislation and this is the first time in over 50 years that a nesting turtle has been officially recorded here. The last recorded nesting was back in 1960 in Golden Bay. In that case, the female was killed and the eggs were stolen.

A surveillance system is in place at Ġnejna, operated by MEPA, the Malta Resources Authority and environmental group Nature Trust.

There are widespread concerns regarding sea turtles' survival that is being threatened by natural and anthropogenic phenomena. One is the decreasing number of male hatchlings in some areas due to disruption caused by global warming, as turtles exhibit temperature-dependent sex determination.

Could occasional turtle nesting, influence in migratory species be linked to global warming such as the rise of sea level, changes in temperature and ocean pollution?

Prof. Patrick J. Schembri from the Department of Biology, University of Malta says that "most female loggerhead turtles will return to the same beach where they hatched to nest. However, a small number will explore new beaches. This is very important for the survival of the species in the long term as otherwise the population will always be restricted to the same few beaches, running the risk of extinction if any of these beaches are lost, for whatever reason.

"The factors which cause a few females to explore new sites are not known, but what is known is that turtles use a number of environmental cues to navigate. Amongst these cues are current patterns, the chemical composition of the water as well as tracing chemicals in sand found on beaches.

"Since sea currents are in part dependent on water temperature characteristics, then temperature changes may indirectly affect navigation and migration routes of turtles.

"Similarly, any changes in the chemical composition of seawater and beach sand (such as changes brought about by 'pollution') may also affect turtle navigation and migration and the use of beaches for nesting."

The loggerhead's sex is dictated by the temperature of the underground nest while incubation temperatures generally range between 26 to 32°C.

According to the professor, "it is the temperature of the nest that plays an important role in determining the sex of the developing loggerhead turtles in the eggs. Normally, warm temperatures will result in more females than males and vice-versa for cooler temperatures.

"One should note however that it is not the air or sea temperature that is important but the temperature of the nest, which is affected by many factors such as the depth of the nest, the type of sand, humidity, where the nest is sited, like for example if there is any shade during part of the day. In short, it is the nest microclimate that is important."

Very little is known about why sea turtles nest on some beaches and not on others.

Schembri says that "many factors influence beach selection but it is not known exactly which factors or even the relative importance of the various factors.

However, he says that currents, physical properties of the sand such as size of sand particles, and chemical properties of the sand have been shown to play a major role.

A protected species

Turtles are sometimes accidentally caught by fishermen and there exists a programme for rehabilitating such turtles.

Schembri says that "turtles are protected species and it is illegal to kill, capture or harm them. Therefore there is hardly likely to be any information on any 'poaching' that may take place.

"Ever since the law protecting turtles has been enforced, the market for turtles (mainly the restaurant trade) has disappeared so there is little point in poaching turtles unless for personal consumption."

John J. Borg, Senior Curator, National Museum of Natural History, also had his views to share on the subject.

Borg says that the loggerhead turtle used to breed in high numbers on most of the Mediterranean beaches with the largest numbers today doing so on beaches in the Aegean (Turkey and Greece) and North Africa, especially along the vast Libyan coastline.

"Climate change can affect the general behaviour of the animal,  but not the choice of a breeding beach. Any form of pollution, like oil pollution, light and sound pollution and any other forms, can have a negative impact on the animal's general behaviour including the choice of breeding beaches.

"Marine turtles have strong site tenacity, that is, they return each year to the same beach to lay their eggs. In some cases, when disturbance is high, they will abandon breeding altogether and return back to sea without laying," Borg says.

Rome study

Prof. Schembri meanwhile says that marine turtles are highly philopatric, that is, the young return to the same beach from which they had hatched: a sort of an imprint.

"A study on the genetic characterisation of the turtle 'Caretta caretta' based on old museum material from Italy and Malta, was carried out in 2011 by the University of Rome and the National Museum of Natural History.

"This study showed that Maltese turtles present in the national collection held at the Natural History Museum had a unique strain, which means that these marine turtles were genetically different from other Mediterranean populations, thus showing how very site specific these animals can be."

So what are Borg's views on the contributing factors to turtles hatching more female eggs?

"In all reptiles, temperature plays a very important role in determining the sex of hatchlings. This has been well studied in crocodilians as well as in marine turtles.

"It is the surrounding temperature during a critical period of embryonic development that determines whether an egg develops as male or female. This period occurs after the egg has been laid, so sex determination in these reptiles is at the mercy of the ambient conditions affecting egg clutches in nests.

"For example, in many turtle species, eggs from cooler nests hatch as all males, and eggs from warmer nests hatch as all females. In crocodilian species - the most studied of which is the American alligator - both low and high temperatures result in females and intermediate temperatures for males."

Article 12 of the Council Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora, together with the Regulation 25 of the Flora, Fauna and Natural Habitat Protection Regulations (L.N. 311 of 2006, as amended) state that the deliberate disturbance of these species, particularly during the period of breeding, rearing, hibernation and migration, is prohibited. And this is why anything that may disturb the turtle from the above is prohibited, at least for the next six months in Gnejna Bay.

In fact, MEPA has said that the "capture, killing, taking, keeping, trade and the deliberate disturbance of these species, particularly during the period of breeding, rearing and migration, is prohibited," adding that although a similar was reported over 50 years ago, no substantial evidence existed on record.

Caravans and cars cannot enter the designated area, camping and bonfires are prohibited and only manual beach cleaning is allowed.

Borg says that usually, the absence of lights and noise as well as predators are determining factors. Egg-laying is a lengthy affair and the animal is at its most vulnerable. Some species have adapted to low light levels while others have not.

Both Schembri and Borg agree that awareness on sea turtles has grown in Malta over the last few years.

Schembri confirms the last time a Loggerhead turtle attempted to nest locally (at Golden Bay in 1960), the turtle was eaten and the eggs were taken.

This time round though, the story has been completely different thanks to the awareness.

According to Borg, a number of NGOs are working very hard on the educational part of conservation with school children as well as adults. Also, people are now more aware of these animals; whenever an injured turtle is encountered out at sea, they normally contact one of the NGOs for assistance.

"Thanks to the annual turtle release activity held jointly by government departments and NGOs, people are becoming more aware of the conservation needs of sea turtles, however there is ample space for improvement."

Borg adds that "the National Museum of Natural History in Mdina also has a section dedicated to marine turtles while plans are underway to expand this visual display highlighting not only the biology and ecology of these fascinating reptiles, but also the threats they encounter".

Isla Harrison
I am an Ecology graduate from Cardiff University in Wales, UK. I have Maltese family and have been going to Ġnejna Bay for years. Any chance of volunteering with the turtles?