Navigation of Sea Turtles

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Navigation of Sea Turtles

• Christina Ryder
• Herpetology
• January 24, 2003

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A Little bit about sea turtles

• from the families Chelonidae Dermochelyidae
• - caretta caretta (loggerhead sea turtle)
• -chelonia mydas (green sea turtle)
• -eretmochelys imbricata (hawksbill sea
  turtle)
• -dermochelys coriacea (leatherback sea
  turtle)
• -lepidochelys kempi (Kemps ridley sea turtle)

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• Loggerhead sea turtle
• Green sea turtle?

Hawksbill sea turtle ?
?Leatherback sea turtle Kemps ridley sea turtle?
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and a little more

• Special adaptations for life at the sea
• -large shells for protection
• -tough keratinous beak to bite
• -modification of limbs to flippers for
  swimming

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The great journey
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from the beginning

• Hatchlings must leave the nest to safely get to
  the sea to find food, shelter, and warm water

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So how do they do it?

• They must rely on the reflection of the moon and
  stars on the ocean, the downward slope of the
  beach, and the lack of vegetation to get them to
  the sea

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Then, Its off to the Gulf Stream

• Once in the water, the baby turtles must find the
  current of the North Atlantic gyre. For as long
  as possible, the turtle swims against the waves,
  away from the coast. They also use the direction
  of the waves to set their compasses for future
  reference.

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Staying in the gyre

• For the rest of its life, except time to lay
  eggs, the turtle will remain in the gyre, relying
  on the waters to provide food and warmth.
• A turtle usually spends about 5 to 7 years
  circling the Sargasso Sea.

• Getting off-course is deadly. The turtle must
  turn south or else the current will carry him or
  her to the frigid waters of England.

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So, how do they do it?

• By using their internal compass and magnetic
  inclinations to sense the angles created by the
  magnetic field.
• By sensing the slight change of angle, the turtle
  is able to make the correct turns to follow the
  current to stay alive.
• 57? ? Florida beach
• 60?? Gulf of Portugal

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So, how does it work?

• The earth has a magnetic field best described as
  lines of magnetic force that flow around the
  planet from the magnetic South Pole to the North
  Pole.

• Turtles brains contain the magnetic mineral
  magnetite used for detection and orientation.

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And then they return

• When the female is mature and is ready to lay
  eggs, she returns to the very beach at which she
  was hatched.
• She digs a hole, lays her eggs, and then returns
  to the ocean.

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How does she get there?

• By swimming , of course!

But how does she know where to go?

• In addition to a sense of direction and guidance
  by their magnetic inclinations, sea turtles have
  map-sense. (They remember the relativeness of
  one location to another.)

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and the whole journey starts over again
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Conclusion

• the loggerhead migration picture mow looks like
  this Hatchlings emerge from their beachfront
  nests at night and head toward the bright light
  coming off the ocean, setting their magnetic
  compasses. Once in the water, they swim directly
  into the waves. Swimming into the waves keeps
  the youngsters heading away from the coast. When
  they hit the Gulf Stream, they ride the current,
  relying on their magnetic inclination compasses
  to tell them when to turn and head south for the
  Sargasso Sea. Then, in late adolescence, they
  find the magnetic inclination angle of the
  Florida beaches and ride it home.

-according to Kenneth Lohmann
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References

• www.cccturtle.org/behav.htm
• www.google.com
• Reptiles and Amphibians. Roger Conant/ Joseph
  T. Collins ed. Houghton Mifflin Company, 1998.
• Sea Turtles Master Migration with Magnetic
  Memories. Science. April 29, 1994 v264 n5159
  p661(2)
• www.unc.edu/depts/oceanweb/turtles/