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Sea Turtles in Puerto Vallarta

The Olive Ridley Turtle (Lepidochelys Olivacea)

By Griffin Page
Naturalist ~ Eco-guide


The Olive Ridley turtle (Lepidochelys Olivacea) is one among the 8 different species of marine turtles that exist in the world. All 8 species are in danger of extinction and 7 of them come to nest on Mexican beaches. Two species are actually endemic to Mexico, which means they are only found here and nowhere else in the world: the Kemp's Ridley (Lepidochely kempii), found in the Gulf of Mexico, and the Black Turtle (Chelonia agassizi), whose nesting area is in the state of Michoacán. Marine turtles are also some of the oldest creatures that ever existed on this planet, some 200 million years of evolution. They have managed to survive that long and are now in danger of becoming extinct; the reason: Human's over exploitation of natural resources.

 

 

Of all the species, the Olive Ridley is one of the smallest in size; small in comparison to the 7 other species of marine turtles, but not small by any of our standards as an adult turtle averages between 26 inches (66 cms) and 36 inches (91 cms) in length and has an average body weight close to a 100 pounds (45 kgs).

 

 

History

 

Turtle fossils dating back to 150 to 200 million years have been discovered. In those days, turtles were much larger than the ones we have today. As can be seen in this picture of the Archelon, the biggest of these ancestral marine turtles, some measured up to 13 feet (4 mts.) long and had a wingspan of 16 feet (5 mts.).

 

 

 

Anatomy

 

The major difference between marine turtles and tortoises is that tortoises are land turtles, they have toed feet, a nail protruding out of each toe and are able to retract their heads into their carapace for protection. Marine turtles on the other hand, have flippers with few nails (usually 2 per flipper) and cannot insert their heads in their carapace. However, marine turtles are better adapted to their environment than land tortoises.

 

Since marine turtles are cold blooded (ectothermic), they are unable to control their body temperature , and so, are found in sub tropical or temperate ocean waters of around 20° Celsius.

 

The Olive Ridley is similar to the Kemp's Ridley, but has a deeper body and slightly upturned edges to its carapace. Its width is about 90 % of its length and an adult weighs around 100 lbs (45 kgs). As in other turtle species, males have larger and more strongly curved claws, as well as a longer tail. This particular species is a slow growing one; they attain sexual maturity between 8 and 12 years of age, their full adult size around 15 years of age and it is believed, can live up to 100 years. Although they are born with one tooth, which they use to break the shell in order to come out of the egg, they lose it rapidly and hence, have no teeth. Their beaks are well adapted to suit their specific feeding needs.

 

Adults are usually olive-grey above and creamy or whitish, with pale grey margins underneath. Newborn hatchlings are almost completely black when wet and medium to dark grey when dry.

 

Migration and Nesting Sites

 

These turtles travel thousands of miles or kilometers between feeding and nesting grounds. Once they reach sexual maturity, between 8 and 12 years of age, the females return to the same beach where they were born in order to lay their own eggs. It is believed that they actually mark the specific location in their memory when they make their way to the ocean from their original birth nest as newborn babies. This is why turtle camps always release baby turtles some distance from the water's edge and let them tread their way into their new home.

 

Strangely, there is a 8 year period between their birth until they reach sexual maturity, called the lost years, where very few turtles are ever seen. They make it to the ocean from their nests and then just disappear for approximately 8 years. It is believed that since the babies aren't yet strong enough to use the ocean currents to get from the breeding to the feeding grounds, that, in fact, the currents actually carry them far from known concentration areas. Because these same currents also carry a multitude of organisms that figure on the turtle's diet, it is suspected that they can feed relatively easily.

 

The Olive Ridley turtles, in Mexico, are distributed along the Pacific coast, including the Sea of Cortez.


The most important breeding grounds for the Olive Ridley are:

 

Western central coast of Mexico - 200,000 nests per year; West coast of Costa Rica - 200,000 nests; Nicaragua - 20,000 nests; Guatemala - 3000 nests; Honduras - 3000 nests; Panama - 1000 nests; Surinam - 2000 nests; French Guiana - 500 nests; Angola (Ambris), Skeleton Coast, northern part of Mamibia - 500 nests; Mozambique - 500 nests; and India - 300,000 ( biggest nesting aggregation still present today).



Other seasonal, but non-reproductive concentrations, occur in feeding areas, like the eastern part of Venezuela or the area between Columbia and Ecuador

 

Feeding

 

This turtle usually migrates along the continental shelves and feeds in shallow waters. They are carnivorous and have quite a large variety of food items on their diet. The well documented data collected from analysis of stomach contents in Mexico show 9 species of gastropods, 26 species of neogastropods, 17 species of pelecypods as well as scaphopods, crustaceans, molluscs, amphipods, isopods, stomatopods, vertebrates and unidentified algae. In simple terms, they eat fish, crabs, shrimp, squid, jellyfish, fish eggs, sea grass and a minute quantity of algae just to name a few.

 

Reproduction

 

These turtles attain sexual maturity between 8 and 12 years of age. The mating occurs principally near the surface of the ocean, close to the nesting beaches or along the migratory routes and is not often observed. If disturbed, the coupling pair may dive down. After the coupling is over, the partners will usually swim separately.

 

As in other species, the male will hold the carapace of the female with the claws of his four flippers. The mating may last for a few minutes to several hours and occurs before and during the nesting season. It is possible that a female may mate with several males.

 

The reproduction season here, in Bay of Banderas, begins in June and ends around December, with a higher percentage of nestlings from July to September. A very interesting fact is that the sex of the hatchling isn't determined in advance by a gene but rather by the temperature during the incubation period. For the Olive Ridley turtle, incubation temperatures around 30° Celsius will produce about half males and half females. Temperatures above 30° Celsius will produce more females and the opposite occurs at lower temperatures. However, at temperatures below 28° and over 32° Celsius, a decrease in survival rate may occur.

 

Once the female is ready to lay her eggs, she will wait for a quiet time when disturbance is at a minimum. As mentioned before, turtles are cold blooded and cannot regulate their body temperature. Because of this, they often choose night time to lay their eggs. Night also offers these turtles better protection from predation and rainy nights seem to be as good a time as any. Let it be known that only female turtles ever return to land and do so only to dig their nest and lay their eggs. Once males have entered the sea, they never return to land.

 

The process of digging a nest and laying eggs is a difficult one for turtles. Apart from being in a completely foreign environment, having to drag close to 100 lbs (45kgs) of weight over the sand for a certain distance, the turtle's vision is poor outside water. She then has to dig, with her rear flippers, a hole of approximately 1 1/2 feet deep (46 cms) and lay an average of 100 eggs. She then has to cover her nest and try to camouflage it. She will do so by shoving sand with her flippers while rotating, creating a pattern much bigger than the original hole and by swinging from side to side, slapping her body on the sand to compact it. If a female is disturbed while digging the nest, she will stop and return to the ocean. However, if the laying of the eggs has begun, she will not stop. During that time, she appears to be in a kind of trance. Well, we know what it's like for humans to give birth, so you can just imagine what laying between 50 to 130 eggs can be like. That is why is of the utmost importance to leave them alone, in peace, and let them carry on with their difficult task.

 

The reproductive cycle is usually annual, but in some cases, turtles may reproduce and nest every 2 or 3 years. It appears that those turtles who travel further during migrations reproduce less often than those residing near the nesting sites which may do so almost every year. During the nesting period, one particular turtle may reproduce 2 to 4 times and so, lay her eggs 2 to 4 times also. The average is 2 nests per reproduction period and the quantity of eggs is higher on the first nestlings and reduces on the subsequent ones. For example, a turtle laying 3 times may produce 130 eggs the first time, 90 eggs the second and 60 eggs the third time. Of course these numbers are just an example and they also vary according to weather, depredation, disturbances and level of health of that specific turtle.

 

The egg size is that of a ping pong ball, perfectly round and is rather soft, unlike a chicken egg, which allows the female to drop them without cracking them. The incubation period varies relatively from region to region. Here, in Banderas Bay, the incubation period is around 40 to 50 days. Other places in the world have shown incubation periods varying between 45 and 65 days and is strongly correlated with temperatures and humidity. In dry, colder weather, it lasts longer than in areas with temperatures around 30° Celsius and a 14% humidity level. Other parameters that influence the length of the incubation period are: sand grain size, organic matter content, clutch size, date of oviposition, and possibly, the proximity to other nests. A shorter incubation period reduces the possibilities for predation and the detrimental effects of bad weather. In 2002 for example, most, if not all the turtle nests in Bay of Banderas and its environs were destroyed by hurricane Kenna.

 

Mass arrivals

 

There are only 2 species of marine turtles that occasionally come in huge numbers to nest on a same beach. Those are the Olive Ridley and the Kemp's Ridley turtles. Mass arrivals or "Arribazones" usually occur every quarter moon (14 to 28 days) and may be repeated two to seven or eight times each season.

 

At the beginning of summer, turtles approach special spots on the shore and during the next quarter moon, thousands of females arrive along a stretch of several kilometers (always less than 10 km). This is thought to be an anti predatory technique and may explain the generation, within short periods of time, of locally restricted populations of hundreds or thousands of females and hence, their success as a species. During mass arrivals, the Olive Ridley turtle shows a cyclic response to temperature, so usually, there are no turtles on the beach at noon. In the afternoon, when the sands becomes fresh, the turtles come onto the beach, increasing their number up to a maximum around midnight, and then start leaving the beach until the next morning. Nesting may extend for two or three nights, and usually, is repeated every last quarter moon until the end of autumn.

 

However, this technique is not always the best approach, especially when the chosen beach is of restricted length as in the case of Nancite and Ostional in Costa Rica. In such cases, the turtles may excavate another turtle's nest in an attempt to lay her own eggs. There may be a high mortality rate in eggs, embryos and hatchlings because the time span between each quarter moon is shorter than the incubation period. This may also happen on longer beaches where the incubation period is longer than 50 days.

 

Because the success of the hatchling of the egg laid in subsequent arrivals is low on small beaches (less than 10 %), it is postulated that the colony is supported by inter-arrival solitary nestlings that lay clutches with higher survival rates. On longer beaches, as in Mexico and India, the survival rate of eggs is usually over 30%, which means that several million hatchlings enter the sea annually. Hence, in the same species, quite different results are obtained with the same strategy.

 

One of the most important nesting beaches in Mexico is that of Playa Escobilla, in Oaxaca, and is counted among the most important nesting beaches in the world along with Nancite (Costa Rica) and the Bay of Bengala (Orissa, India). For example, in 1968, it is estimated that between the 7th and the 10th of august, over 80,000 turtles came to nest on Escobilla. Of course, due to predation, these numbers have diminished.

 

Threats

 

The Olive Ridley turtles, as with many other species of marine turtles, encounter numerous threats through out their lives. The predation begins as early as the incubation period. First, the eggs can be infected by fungi and bacteria. There is also a larvae from a fly, that, normally is supposed to attack only dead or sick eggs, but may sometimes propagate to healthy ones. Also during the egg stage, the predator list may include animals such as dogs, jaguars, foxes, pigs, ants and crabs. During the early stages of life, until they reach adulthood, their predators are, amongst others, coyotes, foxes, dogs, raccoons and coatis, crabs, ants, birds (such as magnificent frigatebirds and pelicans) and fish. Sharks and killer whales are their main natural predators when they reach adulthood, if they make it to that stage at all.

 

Here's a basic list of human impacts on marine turtles worldwide:

 

~ Pesticides, heavy metals and PCBs have been detected in turtles and eggs. The effects have not yet been determined.
~ Oil spills puts turtles at risk. It affects their respiration, skin, blood chemistry and salt gland functions.
~ Garbage can be detrimental to their survival as well. Plastic bags, styrofoam pieces, tar balls, balloons and raw plastic pellets can be mistaken for food and ingested by turtles thus, interfering in their metabolism and gut function even at low levels of ingestion and may cause absorption of toxic byproducts.
~ Where recreational boating and ship traffic occurs, direct collisions and boat propellers cause mortal injuries.
~ Uncontrolled beach development, reduction of nesting beach size by construction of walls and lighting on beaches.

 

It is estimated that only 1% of all hatchlings survive to become adults. The main reason why these wonderful creatures are on the brink of disappearing forever is......humans! Due to over exploitation of the turtles themselves for their meat, eggs, skin and carapace, millions of turtles were slaughtered every year and still are in some areas. Another even more serious problem is the unwanted capture of turtles by commercial longliners and trawler nets. Fortunately, some countries have adopted TED nets (turtle excluder device) and have made them mandatory for commercial fisheries. This type of net has a trap door that opens when a turtle pushes into it, hence releasing it and allowing it to surface to breathe. Millions of turtles drowned annually in the other types of nets. Now, they are pushing for a larger TED in order to allow the escape of bigger sized turtles. As for longliners, a 3 year study, done by the National Marine Fisheries Service in the USA, has demonstrated that by a simple change in fishing equipment from "J" hooks to a type called a "circle" hook, they could significantly reduce the unwanted capture of turtles. Let's hope that countries all over the world adopt these measures in order to stop the rapid decline of these marvelous ocean creatures and thus avoid their complete extinction.

 

Conservation projects

 

Many countries are participating in marine conservation projects such as turtle camps. Some are bigger and include research while others concentrate on protecting eggs in secure nurseries and releasing them after they hatch. In México, there are approximately 500 turtle camps nation wide, of which around 340 are big ones. The larger camps, those who luckily have a little more funding than others, may include specific data collection on the species found in their area and most will also tag adult females while they nest and hatchlings before they are released, and give basic medical assistance to those who may be slightly injured. This supplemental work has great advantages when it comes to marine turtle conservation. The tagging, for example, allows us to count more precisely the number of females nesting on one particular beach and the number of hatchlings that survive and make it back to their nesting grounds years later. In other words, it allows us to determine much more precisely the number of actual turtles in one area, thus giving us important information as to the rate of decline or success of any particular species, thus, also allowing us to make the proper adjustments in order to increase the effect of our efforts in protection and restoration of one species.

 

Education is a big part of marine turtle conservation. It is important to dispel those myths that are causing it's rapid decline. Turtle eggs are not an aphrodisiac; studies have determined that as a fact. More so is that a turtle egg's contents of bad cholesterol (LDL) is much higher than that of a chicken egg, and we all know that even a chicken egg can be bad for your health due to it's high content of "bad" cholesterol. Turtle egg poaching has no reason to exist in our world.....let us tell it like it is.

 

How you can help

 

Should you encounter a female making it's way on the beach to lay it's eggs, here's what to do:

 

~ Stay away from her, at least 10 feet (3.3 meters) and never place yourself in front of it, always stay behind.


~ Be quiet and don't move around, instead, sit quietly and enjoy this wonderful gift life has offered you. Don't forget to get out of the way when it tries to go back to the sea.


~ Don't let people form a circle around her. That can be very stressful to the turtle. Laying her eggs is hard enough for her.


~ If it happens to be nighttime, do not shine any light on it, that may cause her to stop digging and return to the sea, hence, not permitting her to lay her eggs.


~ Call the proper authorities for that area (local biologists or a local turtle camp is preferable) so that they may come and recover the eggs before poachers do their nasty work.


~ Should you encounter a hatching nest, DO NOT TOUCH the baby turtles. Any bacteria, repellent, or food debris can be detrimental to the hatchling's survival. Wash your hands carefully before attempting to help a turtle stuck in debris or having difficulty making it to the ocean. Remember to let it mark it's location, do not put them directly in the water unless it's really necessary.


~ Some organizations collect funds that are distributed to local camps. Don't be afraid to give, your children's future will only be the better for it.

 

They say that our future lies in the hands of our children. That is very true. On your next vacation, bring your children to a turtle camp, teach them or let a knowledgeable person tell them about these marvelous creatures of the ocean. Participate in a baby turtle release program and get the experience of a lifetime. There is little more touching than holding a baby turtle in your hand, giving it a name, a kiss, wishing it luck on it's tough journey ahead and watching it make its way to its home; the sea!

 



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