The Tortoise (Not Turtle!) that Crossed the Indian Ocean

Photo credit: Catharine Muir (Permission granted)

In 2004, a 55-pound Giant Aldabra tortoise washed ashore near Dar es Salaam in Tanzania. Tortoises are land animals, unlike sea turtles, so it floated rather than swam across the ocean. Based on the barnacles that grew on its legs, scientists found that the tortoise had floated all the way from the Aldabra Atoll in the Seychelles over 450 miles away. The tortoise likely washed away during a strong monsoon and was afloat for several weeks or months along the South Equatorial Current with the westerly monsoon winds before ending up on shore.

Guiding Questions

  • What weather patterns were necessary for the tortoise to make this journey?
  • Which wind and current patterns allowed the tortoise to move East to West?
  • The tortoise washed ashore in December; which monsoon season was this?
  • What adaptations allowed the tortoise to survive starvation for that long?
  • How does this compare to the (intentional) migrations of sea turtles?
  • How are tortoises and sea turtles related?

Datasets

Download a playlist for this module

  • ClimateBits: Monsoons

    This video gives background information about the summer monsoon. In the winter, the monsoon direction reverses over the Indian Ocean, bringing wind and rain to East Africa.

  • Loggerhead Sea Turtle Tracks

    Turtle migration serves as a fun comparison to this unusual story, and can launch discussion about biological adaptations of turtles and tortoises.

  • Ocean Surface Winds

    There is a tie between surface currents and surface winds, and both likely contributed to the tortoise's movement.

  • Sea Surface Currents and Temperature (vegetation on land)

    The South Equatorial Current flows East to West in the Indian Ocean and can be seen in this dataset. Turn on the Country Names and Ocean Currents layers to see the locations and names of the the Seychelles and coastal Tanzanian currents.

External Resources

Cross-cutting Concepts

  • C1: Patterns
  • C3: Scale Proportion and Quantity

Disciplinary Core Ideas

  • ESS2.C: The Roles of Water in Earth's Processes
  • PS2.A: Forces and Motion