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.