The sea turtle is one of the most ancient creatures on Earth. Fossil records go back 150 million years. Some estimates indicate it first appeared 230 million years ago.
Whenever it was that the first one crawled out of the primordial ooze, they are among the very few existing members of the animal kingdom who have watched the dinosaurs evolve and become extinct. Sadly, the sea turtle itself is facing a very high risk of extinction in the foreseeable future.
I thought sea turtles were found in all the oceans.
That's right. Sea turtles are found near all continental land masses except Antarctica. Saltwater reptiles, they are cold-blooded and get their body heat from their environment. This limits them to the more temperate oceans.
Aren't there lots of different kinds?
There are seven species of sea turtles. Five of them - the Loggerhead, the Green, the Hawksbill, the Olive Ridley and the Leatherback - are widely distributed. The Kemp's Ridley is mostly limited to the Gulf of Mexico. The Australian Flatback is found only in the coastal waters of northern Australia and the Gulf of Papua, New Guinea.
I read that they are protected.
The United States passed The Endangered Species Act in
1973, which prohibits hunting, injuring or harassing sea turtles. This even restricts such activities as riding sea turtles as it puts them under stress. Many other countries have passed similar laws. International trade in sea turtle parts or products is also illegal under an agreement known as CITES (Convention for International Trade of Endangered Species of wild fauna and flora). This agreement was signed by 114 countries. Despite the agreement, trade still continues in items such as tortoise shell for jewelry and ornaments, and small leather goods.
So these laws don't help the turtles?
These laws are helping to a certain degree. Turtles are no longer being killed in vast numbers for food, and their nesting sites are often protected to prevent poachers from stealing eggs. Some native peoples in various parts of the world continue to hunt sea turtles as a part of their traditional diet, but turtle soup is no longer served as a delicacy in expensive restaurants.
Then everything is under control, isn't it?
No, it isn't. Hunting turtles is only part of the problem. Many turtles are killed incidentally by being caught in fishing gear. Although they spend most of their life in the water, turtles breath air. When they are asleep or resting they can stay submerged for up to two hours. When they are active they must go to the surface for air every few minutes.
Shrimp boats use nets that trap and drown more than 10,000
turtles a year. In addition to the deaths from shrimp fishers, thousands of turtles die every year when they are caught in longlines, driftnets, gill nets, and other fishing gear.
Ten thousand -- is that an important number? How many sea turtles are there?
There is no way of knowing the global sea turtle population. The only figure available is the count of nesting females. In most developed countries the nesting sites are protected and monitored. All published figures are estimates based on reports dating back not much further than the early 1990's.
These figures can vary due to two facts. Depending on the species, the females lay between 2 and 9 times per season. Most species lay at intervals of 2, 3, or more years except for the two Ridley species which lay every year.
On the basis of counting nesting females, population estimates range from less than 1,000 for the Kemp's Ridley to 800,000 for the Olive Ridley. Of the rest, only the Green with 200,000 nesting females has a significant population.
Still, 10,000 killed annually out of over one million females -- don't the females lay several hundred eggs each time they nest?
Taking all seven species as a whole, each individual nest contains an average of 150 eggs. However, we're talking about reptiles, which have a very high offspring mortality rate. In a normal biological rhythm only a few offspring from each nest live to maturity.
The most fecund species, the Olive Ridley (which also has the largest population of nesting females), produces 105 eggs per nest, two nests per year, and nests annually. While a few species live as long as 80 years, the breeding period of the females is unknown. Additionally, it takes between 10 and 50 years for sea turtles to reach sexual maturity - 25 years is the average.
What I don't understand is this -- if the sea turtles have been around so long, why are they endangered now?
Because there is another very serious threat which is only recent, relatively speaking. Pollution of the ocean is a problem : litter and marine debris have been proving deadly to sea turtles, particularly plastics and oil spills. Hawaii and Florida have recently observed the presence of a disease called fibropapilloma, which causes the growth of large tumors on the soft tissues of turtles. It appears to be fatal.
Over and above pollution and fibropapilloma, the gravest danger to the sea turtle is coastal development and habitat degradation. As urban sprawl continues to encroach on shorelines, sea turtle nesting beaches are lost each year. Unfortunately, adult females nest only on natal beaches. They return to the beach on which they were born. If that beach is denied them due to erosion or fortification to protect beaches from erosion, then the females generally will not lay their eggs. This means that, with time, groups of turtles belonging to particular beach areas will disappear. Furthermore, there is no interbreeding between groups.
Last year we spent two weeks in a condo on the beach in Florida. There were miles of open beach, and the turtle nests were fenced off to protect them. So what's the problem?
Every year Florida beaches have the highest number of turtle nests in the United States. Florida also has a very high number of residential and commercial buildings on the beach. But if you are living in or visiting Florida during the nesting season (March or May 1 through October 31), chances are you will not see any turtle activity because it takes place in the dark. And that's the problem.
The female sea turtle emerges from the ocean at night, crosses the beach to just beyond the high tide mark, digs a hole in the sand with her flippers, deposits the eggs, covers them with sand, and returns to the sea. Simple isn't it? The problem is that lights will detract and confuse her, causing her to return to the ocean without laying her eggs.
More seriously, if the female does nest and lay eggs, there is a further danger when the hatchlings emerge from the nest. This takes place 50 to 65 days after the eggs are placed in the nest.
The tiny hatchlings break through their papery eggshells beneath the sand covering the nest. No one little turtle is strong enough to break through the sand by itself, but with periodic thrashings the entire nest will burst out of the sand together. They immediately scramble for the ocean. Moving quickly from the nest to the water is critical for their survival. This is always done at night so they are not exposed to hot sunlight.
The hatchlings instinctively head for the brightest horizon, which is the sky over the open sea. If there are artifical lights they will be attracted to those, and they will move towards street lights, porch lights, interior lighting visible through windows, even bonfires. Failing to find their way to the sea, the young turtles are eaten by crabs and other predators, felled by exhaustion, killed by the morning sun, struck by automobiles in parking lots and roads. A single light near a nesting site can be responsible for the death of an entire nest. Under such circumstances the survival to maturity rate drops to one in a thousand.
Oh. I didn't know that. But that's just in Florida, isn't it?
Unfortunately, the answer is "no". Wherever there are nice beaches and a warm climate, you'll find hotels, resorts, and vacation rentals. Those are the beaches the sea turtles like for nesting. They've been doing it for millions of years, but apparently that doesn't count for much, does it?
Florida Power & Light Company
Florida Fish & Wildlife Conservation