Over 100,000 Sea Turtles Nest at the Same Time. How?
November 9, 2015 - Hundreds of thousands of olive ridley sea turtles all arrive together to lay their eggs near Ostional, Costa Rica—and we know little about how they coordinate that feat. Vanessa Bezy, a National Geographic young explorer grantee, is trying to find out more. To test the hypothesis that pheromones trigger the nesting behavior, she's giving a number of turtles that are swimming toward the nesting site a zinc sulfate solution that willtemporarily block their sense of smell, which will let her see whether they're less likely to come ashore. The solution, which wears off within five days, doesn't harm the turtles. The study, approved by the Costa Rican government and the University of North Carolina's biology department, should provide invaluable information to conservation groups hoping to protect these animals.
Learn more about olive ridely sea turtles.
Transcript
ON-SCREEN TEXT:
A few times a year a biological mystery happens on a Pacific
beach in Costa Rica.
Normally solitary, up to 200,000 olive ridley sea turtles
come together to lay their eggs in the sand.
Locals call it an arribada. Spanish for “arrival”.
VANEESA BEZY, NATIONAL GEOGRAPHIC GRANTEE, UNIVERSITY OF
NORTH CAROLINA:
My main interest is understanding how or specifically what
the mechanism is for these sea turtles to synchronize their nesting behavior.
We do not know why the sea turtles specifically come to
Ostional.
ROGER BROTHERS, RESEARCH ASSISTANT, UNIVERSITY OF NORTH
CAROLINA:
Sea turtles are renowned for their ability to travel
extremely long distances specifically as young turtles before returning to the
same geographic are where they hatched to lay their eggs as adults. It’s a
behavior known as natal homing that exists in all species of sea turtles but we
really don’t have a good idea for how they do it.
VANEESA BEZY, NATIONAL GEOGRAPHIC GRANTEE, UNIVERSITY OF
NORTH CAROLINA:
It’s possible that a sea turtle has a pheromone that they
secrete into the ocean and that perhaps the concentration of this chemical
reaches some sort of threshold were all of a sudden the turtles know that it’s time
to nest and come up on the beach at that point.
If the sea turtle needs to smell a pheromone or be able to
perceive it then they need their sense of smell in order to know that it is
time to do this mass nesting event.
We are taking a boat that we hire with a local fisherman out
to the offshore waters of Ostional. And we are about 2 miles of the shore
Once we reach that area we are looking over the horizon for
aggregations of sea turtles in the water.
Once we find the turtles, Roger is helping me in going into
the water and safely capturing them and bringing them unto the boat.
ROGER BROTHERS, RESEARCH ASSISTANT, UNIVERSITY OF NORTH
CAROLINA:
Some days they are more likely to swim way and try to escape
and other days they don’t seem to mind.
VANEESA BEZY, NATIONAL GEOGRAPHIC GRANTEE, UNIVERSITY OF
NORTH CAROLINA:
The experiment that we are focusing on is trying to see
whether if we take away that sense of smell if the sea turtle is less likely to
come up on the beach and participate in a mass-nesting event.
Once we have the sea turtle on the boat we are doing to
different treatments that we are applying to the nostrils of the sea turtle. We
are doing one treatment and this is seawater and that is a control. And the treatment that we are actually doing
experimentally is called zinc sulfate and this is a chemical that temporarily
anesthetizes the olfactory bulb of sea turtles.
So the sea turtle will be temporarily unable to smell anything.
In the few days leading up to a mass nesting event that we
are expecting, we’ve been going out on
the boat and capturing as many sea turtles as possible. Before we release the
turtle we dry the carapace and using spray paint to mark a line either
horizontally or vertically depending on the treatment. And then we release the
sea turtle.
During every mass-nesting event we always have people on the
beach surveying the beach in transect surveys to count the number of nesting
females. I have these volunteers looking for the females that we have marked to
see how many of each type of sea turtle is actually coming up on the beach to
nest.
I certainly don’t think this is a question I can answer in
the scope of my PhD so my hope is that I can then move forward and take this as
a career worth of research that I can keep trying to answer more questions for.