All eight species of sea turtles are threatened or endangered, primarily because of the destruction of their breeding grounds, poaching of their eggs for food, and marine pollution. Sea turtles spend almost all their lives at sea, but like all reptiles, the females must lay their eggs on land. When they come on shore, sea turtles have to contend with predators, poachers, and loss of their breeding beaches to seaside hotels and resorts. In some places, coastal pollution has destroyed their food supply of shallow water grasses and seaweeds.
In the ocean, adult sea turtles have only two enemies, sharks and people. Many are accidentally tangled in fishermen's drift nets and long lines. These air breathers drown when they cannot reach the surface. Some sea turtles swallow floating pieces of plastic, mistaking them for jellyfish. The plastic blocks other food from getting into their stomachs, and the turtles starve. Some sea turtles have been found with tumors growing on their bodies, possibly a result of marine pollution.
Many islands and coastal areas now protect breeding sea turtles, but to sustain their populations we need to be able to protect them throughout their range. Yet little is know about their habits and migration routes. Radio tags on some sea turtles allow them to be tracked by satellites.
The Kemp's ridley (Lepidochelys kempii), the smallest of sea turtles, is also the most endangered. (The Kemp 's ridley was named in 1880 for Richard Kemp, a fisherman who shipped specimens to Harvard University from Key West.) It is concentrated in the Gulf of Mexico (yet rarely is found in nearby Caribbean water). It sometimes swims and drifts northward along the Atlantic coast and even crosses the Atlantic to Europe and Great Britain. Some even reach New England on the seasonal migration up the coast.
The nesting and breeding areas of the Kemp's ridly remained a mystery for many years until a film taken of the Mexican coast in the 1940's accidentally revealed the nesting site of thousands of ridley sea turtles. They lay their eggs on a beach at Playo Rancho Nuevo, in Tamaulis, Mexico. From this beach on the eastern coast of Mexico, baby ridleys enter the water and may be carried by currents around Florida and up the western Atlantic coast and across to Europe.
In 1990, biologist Richard Byles placed radio transmitters on six adult female Kemp's ridleys and tracked them by NOAA satellite until the transmitters fell off ( they were designed that way) or quit working. The satellite used GPS-Global Positioning System - to locate their position every time it passed overhead.
The radio tag could only transmit a signal to the satellite when its antenna was out of the water, that is, when the turtle surfaced to breathe. In this way, researchers got information not only about a turtle's migration path, but also about how long she stayed under water (96% of the time!). Byles learned from this project that adult female ridleys migrate along the coast of the Gulf of Mexico in shallow water less than 150 feet deep, where they may encounter fishing nets and pollution from oil drilling operations.
Track the migration routes of six rare Kemp's ridleys.
- Review the information provided in the background with students.
- Trace the route of the Kemp's ridley on a chart of the Gulf of Mexico and the Atlantic Ocean.
- Superimpose the path of the Gulf Stream system onto the map.
- Discuss, "How do the two features overlap?" (The Gulf Stream is the ridleys' transport.)
- Using Byles' research data on 6 adult Kemp's ridleys (which he named 7660, 7661, 7662, 7663, 7664, and 7665), have 6 teams of students choose one turtle each to follow. (Perhaps they could invent more exciting names for their subjects!)
- First, students need to make a scale for their maps.
Have students measure the distance between New Orleans (at the mouth of the Mississippi Delta) to the northern point of the Yucatan Peninsula and then compare that distance to the scale on an atlas showing the same area.
- Plot the turtle's migration path from June 15, 1990-August 31, 1990.
- Use a ruler and the scale to compute distances traveled. Compare maps to determine which turtle traveled the farthest, which one the least.
How far away did each turtle end up from the nesting site of Playo Rancho Nuevo at the end of the recording period?
Where do most of the females prefer to "hang out?"
What other kinds of information can you deduce from the maps?
Classrooms with access to a computer modem will also be able to receive satellite-generated turtle-tracking data at the same time as marine researchers.
Tracking Right Whales
WhaleNet is tracking Right Whales in the Atlantic Ocean using tags that sent position data to satellites. You can use that data from WhaleNet in the same way as the data for sea turtles. WhaleNet also makes tracking maps available for the area surrounding the whale's location.
The loggerhead route
On a chart of the Atlantic Ocean, map the path a young loggerhead turtle takes (from Atlantic coast to the Sargasso Sea, at the center of the North Atlantic Drift), as explained in the second story of A Tale of Two Turtles. Loggerheads have also been tracked by satellite.
Find at least three ways sea turtles are different than pond turtles (possible answers: size, habitat, diet, sea turtles can't withdraw head and flippers into shell, back flippers are paddle-like, etc.).
- map of the Gulf of Mexico
- colored pencils
- map of North Atlantic Drift (including through Straits of Florida, Gulf Stream, and across to Europe)