With heads never hidden, sea turtles have glided proudly through more than 175 million years of existence. Tragically, the world's eight species of sea turtles have all suffered serious declines in population just in the past 100 years. These majestic reptiles, remarkably adapted to life at sea, are affected directly and indirectly by human activities and deserve our concern and respect.
All sea turtles begin their lives as tiny hatchlings on a beach. They shuffle towards the ocean and venture out, their destinations still somewhat of a mystery to researchers. It is thought that baby turtles spend their earliest, most vulnerable years near large beds of sargasso weed, which provide protection and nourishment for growth. They are then seen in nearshore feeding grounds when they are approximately the size of a dinner plate. They grow slowly and, depending on the species, they are between 15 and 50 years old when they reach reproductive maturity. When it is time to nest, the female turtle will usually return to the beach where she was born to lay her eggs. It is thought that some species live over 100 years, but there is no way to determine the age of a sea turtle from its physical appearance.
There are differences between the species; for example, in appearance, food preferences, and habitat preferences. For fascinating information about each species of sea turtle, visit EuroTurtle and the Caribbean Conservation Corporation's Sea Turtle Species of the World. You'll want to explore these two sites fully since you will also find distribution and population information, several tables of comparative size and reproduction information, maps of nesting beaches, and much more.
Turtles have been harvested for their flesh, oil and shells, and their eggs are sometimes robbed from their nests. Plastic bags and other plastic debris have also been responsible for turtle deaths because they are confused with one of the turtles' favorite foods - jellyfish. They are also threatened by fishing, boat collisions, and all sorts of modifications to their nesting beaches which decrease the hatchlings' chances of survival. Lights and airplane noise associated with developed areas can disturb nesting turtles and disorient hatchlings. Newly hatched turtles may mistakenly travel towards artificial light rather than towards the moonlit ocean, and they will starve to death as a result.
Data Exercise
At the Watamu/Malindi Marine National Park and Reserve in Kenya, the community is involved in conserving turtles through the observation of their nests. If the nests are below the high-water mark, or an exceptionally high tide is expected, a decision is made to move the turtle nest. If a nest is inundated by sea water the eggs will all die. In addition to nest relocation, the volunteers conduct community education programs and collect data on sea turtle nesting and bycatch. Let’s explore some of the sea turtle data from the Watamu Turtle Watch (WTW) program.
Print out the WTW 1999 hatching data.
In the top table, complete the last column, which is the hatching success rate. The first one is completed for you (76%).
Next, complete the data summary table in the bottom, left corner of the worksheet. Here, you are asked to calculate the number of natural and relocated nests, average incubation period, total number of turtle eggs, and the 1999 average hatching success rate.
Based on the number of natural versus relocated nests, and the average success rate of hatching, can you conclude that the community's monitoring efforts are beneficial to the sea turtle?
Now let's examine WTW's nesting data
The first graph demonstrates combined yearly turtle nesting amounts in Watamu and Malindi, Kenya.
- What are the mean and median of the data set?
- What is the range (difference between the lowest and highest values) of the data?
- Despite the graph showing a drastic increase in the number of turtle nestings, we cannot assume that the increase is due entirely to the community’s efforts. What other reasons could there be for the increase in turtle nestings?
The next graph shows yearly turtle nesting amounts on Watamu beach by month.
- From 1997-2002, what month typically had the most turtle nestings on Watamu beach? How many nests have occurred in that month?
- In what year were the most turtle nestings?
- In what single month and year were the most turtle nestings from 1997-2002?
The final graph reflects the yearly turtle net releases by Watamu Turtle Watch at Watamu and the Mida Creek.
- 2001 saw a dramatic increase in the number of net releases. What is the percent increase in net releases between 2000 and 2001? (Ex. Between 1998 and 1999, net releases increased 156%.)
- What is believed to be the cause of this increase in net releases?
- What is the percent increase in net releases between 2002 and 2003?
- What was the cause of this increase in net releases?
The World Society for the Protection of Animals (WSPA) has issued a Turtle Alert, challenging tour operators to adopt turtle friendly practices. You can help, too, by being aware of the problems which are threatening sea turtles and by doing your part to take care of the oceans and beaches for all species.
For other sea turtle activities, take a look at the Gulf of Maine Aquarium's All About Turtles section (includes some information on freshwater turtles, too). You can plot the migration of a sea turtle and take some online quizzes on the Caribbean Conservation Corporation site or track more sea turtle nests with the Folly Beach Turtle Watch Program. And don't miss the Education page of the EuroTurtle site. Additional resources can be found on the Bridge's Sea Turtles page.
If you have questions about the Data Tip of the Month or have suggestions for a future data tip, contact Lisa Lawrence , Bridge Webkeeper.
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