Sea turtles are an important part of cultural history for people all over the world. Ancient myths and legends present the turtle as a symbol of strength, stability and wisdom. A Chinese myth tells the story of the creation of the earth occurring on the shell of an immense turtle. Many other cultures, such as the Greeks and Egyptians, considered the turtle to be sacred. In Bangkok, Thailand, for example, turtles are a sign of immortality. Even today, people give special significance to turtles. They are beautiful, graceful animals, very important to both the environment and to societies both as food and for trade.

There are eight different species of sea turtles alive today:

The Green Turtle (Chelonia mydas) is a circumglobal species and is the most common of the eight sea turtles. The green turtle can be recognized by a single pair of scales in front of the eyes rather than 2 pairs of scales, which most sea turtles have. They are one of the largest species of sea turtles: their shells can be up to 3 ft long, and they can weigh up to 300 lbs. They are called green sea turtles for the color of the fat under their shell, not for the actual color of the shell, which can range from a greenish shade, to brown, black, or even gray. The green turtle feeds on seagrasses and seaweed. Its important nesting and feeding grounds are in the tropics. It has long been harvested for meat and eggs in Costa Rica, Caribbean, Indonesia, and Panama. Its cartilage is used in Asian countries for turtle soup.

The Black Turtle (Chelonia agassazii), which is named for the black or gray color of its shell, is confined to the Eastern Pacific Ocean. It is protected in the Galapagos and nominally in Mexico. They are still subject to illegal harvest, and are on a decline.

The Flatback Turtle (Natator depressus) live only in the waters of Australia where it is protected by law, with the exception of aboriginal harvest. It is named for its flat shell, and can grow up to 39 inches long and 198 lbs.

The Loggerhead (Caretta caretta) has an anti-tropical distribution. It is found in Northern and Southern Indian Ocean, Australia, Japan and the Southeastern US. The loggerhead can be identified by its large head as well as by a reddish brown carapace (upper shell) and dull brown or yellow plastron (lower shell). The loggerhead can grow between 32-41 inches and can weigh up to350 lbs. This turtle doesn’t suffer from poaching or capture for meat, but rather from accidental capture. It has powerful jaws for eating shellfish living on the bottom of the ocean.

The Hawksbill (Eretmochelys imbricata) is subject to intense intentional trade. Its beautifully patterned shell is a source of tortoiseshell used to make jewelry and combs. Its narrow head and beak make it look like a hawk, owing to its name. This is one of the smaller sea turtle species. It only grows 30-36 inches and weighs100-150 lbs. It is common on tropical reefs in the Caribbean islands and Australia. It is smaller than the green sea turtle and its shell is reddish brown with yellow streaks. It feeds on encrusting animals such as sponges, sea squirts barnacles, and seaweed.

The Olive Ridley (Lepidochelys olivacea) nests mainly in the Pacific Ocean, around Costa Rica, Mexico and Nicaragua, as well as the Northern India Ocean. It is the most abundant species of sea turtle, as well as one of the smallest, weighing less than 100 lbs. It is olive green in color, giving it its name.

The Kemp’s Ridley (Lepidochelys kempi) is the rarest species of sea turtle as well as most endangered. Kemp’s Ridley is the smallest sea turtle, only growing to be 24-28 inches and weighing 77-100 lbs. Its carapace is olive green, and its plastron is yellowish. This turtle only nests on one beach in the world, in Rancho Nuevo, Mexico. In 1942, in only one day, 42,000 Kemp’s Ridleys could be seen nesting on this beach. In 1995, there were only a total of 1,429 nests.

The Leatherback (Dermochelys coriacea) is exploited for eggs. Its Atlantic colonies seem to be secure from disruption, but other sites have declined. It is the largest sea turtle- growing up to 7ft long and weighing at least 1,200 lbs. Instead of a hard shell, it has thin, tough, rubbery skin. Five distinct ridges are formed by small bones buried in their skin. Its carapace is black with white spots while the plastron is whitish to black. This turtle lives in the open ocean, it can dive the deepest and travel the furthest of any other sea turtle. Its body shape is very streamline; it has powerful front flippers to aid in strong swimming. It is rarely seen except on nesting beaches. Jellyfish are the main component of their diet.

Reproduction in sea turtles:

Mating: During the mating season, all species of marine turtles migrate from feeding areas to mating areas. After mating, the males then return to foraging areas while the females proceed to nesting beaches. Some turtles migrate more than 2600 km, but most travel less than 1000 km. Female turtles do not usually reproduce every year, except for Kemp’s Ridley. Males may breed every year. Mating can occur anywhere in the water but usually occurs at the surface. Mating is not gentle. The male bites the female’s flippers and neck. Her shell gets clawed from the male’s large claws on the hind and front flippers that hold him in place. The male may also get attacked from other males during this process. Males will bite other male’s tails and flippers. Turtles can stay together while mating for about 10 hours.

Nesting: Most females lay several clutches of eggs, which reduces the likelihood of all eggs being lost. This can be done at 2-week intervals. When nesting, turtles generally escape the heat by creating their nests at night, except for the L. kempi and N. depressus. Eggs hatch after 6 to 13 weeks of incubation depending on the temperature. They generally hatch in the early evening. They can tell whether it is evening or daytime based on the temperature of the sand. They dig toward cooler sand; if they start digging and the sand gets progressively warmer they wait until the sand cools. If they hatched during the day they would have to face excessive heat and predation.

Navigation: After hatching, sea turtles primarily use vision to find the sea, orienting themselves toward the brightest light, presumably the moon. They move away from elevated silhouettes, such as sand dunes and vegetation. Turtles also rely on wave cues to swim offshore, moving toward approaching waves. They sense the wave motion under water by monitoring the sequence of accelerations they experience in the water column. Loggerhead and leatherback hatchlings use internal magnetic compass orientation. Turtles emerge from their nests without an established directional preference. They acquire a directional inclination while crawling on the beach toward a light source. This sets their magnetic compass. They do not have a polarity-based system but an inclination system, which means they follow the intensity of the earth’s magnetic field and not the poles.

Conservation: Sea turtles worldwide are being protected under the endangered species list and by federal agencies. Efforts are being made to develop local help and to educate locals on the importance of these marine reptiles, not only for the future generations, but also for the health of the environment. Unfortunately, sea turtles are still being killed in drift nets, disoriented by street lights, taken as eggs for alcoholic beverages, and are killed as adults for souvenirs, food and shell products. Worldwide, help is needed from both young and old to save these remarkable ancient, endangered animals. Currently, there are several different attempts being made to help protect these species and increase their populations. Shrimp trawling is a large problem for sea turtles, many get caught in the nets and drown. TED’s (Turtle Exclusion Devises) have been developed to reduce sea turtles getting caught in these nets. TED’s are trap doors in the nets that allow the sea turtles, but not the shrimp to escape. Shrimp farms are also being started. Instead of harvesting the shrimp, which can cause the accidental capture of the turtles as well as other marine animals, shrimp are being raised in farms. Turtle hatcheries have also helped reduce the decline of sea turtles by removing the eggs from nests where they may be eaten by predators or removed by poachers. The eggs are taken to the hatchery where they are incubated and later released.

• A projector - VPU
• Projector screen
• Lab top computer-with Microsoft Power Point software

• Chalk, chalk board (white board or large papers with markers will suffice)
• Small paper cups (enough for two for each student, or for each group if they are divided into groups)
• Plastic spoons (enough for each student or group)
• Several bags of M&M’s (enough to fill each cup half way. Skittles can be substituted for M&M's, Pop Rocks can also be incorporated for better demonstration.
• Paper and pencils for students to write.

Engage: The teacher may want to engage students in this topic by asking if any students have seen live sea turtles. Offer examples of seeing them on the beach or at Sea World. Ask what they know about turtles. The teacher should then introduce this topic by explaining the importance of sea turtles and their conservation. Inform the students about the destruction that human activity can cause. For example, the destruction that shrimp trawling causes to marine communities, especially sea turtle populations. This lesson will discuss these concepts in more detail, but it would help the students to have some prior knowledge.

Preparation:

Activity 1: Identification of Sea Turtles

The teacher will need to make colored handouts of the different turtles. Divide the students into groups, give a different picture to each group, and have them discuss the characteristics of the turtle and have them to try to identify the species from these characteristics. Write the names of the eight sea turtles on the board for the students to chose from. After about 5 minutes of group discussion, continue with the Power Point presentation and have each group describe the turtle they were given, telling what they noticed about it and what species they thought it was.

Activity 2: Slide Show of Turtle Identification, Reproduction, Navigation, and Conservation

The class will need to provide access for a Power Point presentation. This will include a computer and VPU projector, as well as a projector screen. If these aren’t available, an overhead projector and transparencies should work.

Activity 3: M&M-Shrimp Trawling Analysis

Divide the class into groups of 4 or 5. Each group will have 2 plastic cups, a spoon, and some M&M candies. The teacher will need to tabulate each group’s results separately and record them on the board to discuss among the whole class. Then tabulate all the findings to obtain the group’s total results, and discuss this in comparison to actual results of sea turtle capture that are occurring around the world.

Activity 1: The class should be divided into groups. Each group is giving a picture of one of the turtles. Explain that they are scientists and they just found this turtle on the beach. They have no idea what this turtle is, and want to identify it. What characteristics does the turtle have that can be used to identify it? Write the names of the species on the board; explain that the turtles are often named based on their appearance. Have the students discuss the characteristics they noticed with the whole class and whether or not they came up with the right name.

Activity 2: Beforehand, download Power Point presentation from attached web site. These pictures will include images of turtle identification, navigation, reproduction, and conservation. Go through each turtle identification slide; discuss the characteristics that the students noticed and what species they thought it was. Take note of the different morphology structure of the shell and facial features. Comment on the fact that many of the turtle’s names and identification are based on physical features. Explain any identifying characteristics, habitat, diet and their endangered status that the students don’t mention. Go through the rest of the sections, asking the questions provided on the slides and discussing the concepts before continuing on to the next slide. If the teacher doesn’t have access to Power Point, overheads with the pictures can be used, and the background information should suffice for discussion.

Activity 3: Divide the class into groups of 4 or 5. Give each group a spoon, an empty cup, and cup of M&M’s (or Skittles). The spoon represents the shrimp trawling nets, the M&M’s will represent different marine animals, as well as sea turtles, the cup full of the M&M’s represents the ocean full of fish, and the empty cup represents the boat holding the catch. Assign a specific color to sea turtles and to the different captured organisms (such as shrimp, halibut, tuna, dolphins, bottom dwelling marine organisms, etc), that the students choose or that they have studied in class. Each student will take a spoonful of M&M’s out of their cup, placing it in the second cup, and record the number of each color, in other words, organisms, that they caught. (Pop Rocks can be substituted to represent shrimp. They are smaller and more difficult to catch, demonstrating the large amount of bigger species that end up being caught in the attempt to catch this small species.) The group will compile the results and share them with the class, these will be written on the board by the teacher. Have each group add up the total catch of each color and write this total on the board. If the class is learning fractions or percentages, this can be practiced by having the students determine the fraction or percentage of shrimp caught from the total catch. If not, simply have the students subtract the total number of shrimp caught from the overall total in order to see the amount of bycatch that results in shrimp harvesting. The teacher should then discuss the findings and overall costs of trawling and net fishing to the marine environment. Discuss why this is decreasing sea turtle populations, and what is being done or can be done to prevent this (TED nets, etc.). In addition, discuss the conservation efforts exist to help protect these species (various conservation groups, turtle farms, etc.). Have the students come up with ideas on what we can do to reduce such bycatch of other marine species as well.

Download our PowerPoint Presentation on Sea Turtle Biology and Conservation. (11.6 MB)

Question 1: What kinds of characteristics are used to identify sea turtles?

Question 3: What human impacts are influencing the destruction of nesting beaches? What is the overall effect of shrimp trawling and massive net fishing on marine organisms? What can be done to prevent these?

Question 4: What are your ideas for conserving these declining, fragile sea turtle populations? And what can you do to help?

Go back over the slides of sea turtles and ask the students to explain what they have learned about each one. Ask them what the major factors that adversely affect sea turtle populations and habitat are. Ask them to repeat any interesting myths or ideas that they learned and any possible questions they might still have.

As a final activity to get the students to stand up and talk in front of each other and practice reading aloud (if reading aloud is a task appropriate for the age group), we allowed each group to select a note card with an interesting fact for the students to take away from the lesson, that might not have been touched upon in the presentation. Here are some suggested facts for this activity:

• Only 1 in 1,000-10,000 baby sea turtles survive to adulthood.
• Before TED’s were introduced, 55,000 sea turtles were killed a year because of commercial fishing.
• While sea turtles are developing in the nest, the sand temperature determines whether it will be a male or female. Cooler sand gives more males, warmer sand gives more females.
• Baby sea turtles break out of their shell with a sharp tooth, which soon falls off. They dig out as a group effort; it takes several day to dig out of the hole.
• Some scientists believe that sea turtles can navigate by detecting the angle and intensity of the earth’s magnetic field.

A coloring book can also be printed out for the students if it is age appropriate. The web site for the Year of the Ocean provides a coloring book with for teachers to print out for their students. This coloring book provides further information on sea turtles for the students. It can be downloaded at this address: http://www.yoto98.noaa.gov/books/seaturtles/seatur1.htm

After this lesson, the teacher can suggest to the students to read about sea turtles and conservation. They can go to Internet sites or contact companies that are involved in sea turtle conservation. Have the students adopt a sea turtle or volunteer for organizations that are involved in researching sea turtles. Other information about other organisms that are affected by shrimp trawling or animals that are endangered that the students may want to know about, can be found by going to the library or looking on the internet.