Unraveling the mystery of mass-nesting sea turtles

Methods

Summary

We will test whether olive ridley sea turtles use olfactory cues (such as pheromones) to coordinate mass nesting behavior. We will capture adult female sea turtles during random searches in the offshore waters of Ostional, Costa Rica in the days just prior to an expected mass nesting event.

Sea turtles will be caught by hand using the turtle rodeo technique [1]. Briefly, when a turtle is sighted at or near the surface and within approximately 1 - 5 m of the boat, the observer will jump into the water and capture the turtle by holding the anterior and posterior medial section of the carapace. The turtle’s head will be lifted up to keep the front flippers out of the water until it can be safely hoisted onto the boat.

We will randomly treat the nostrils of these sea turtles with either ZnSO₄ or saline. ZnSO₄ reversibly anesthetizes olfaction in marine turtles for durations of 1 – 5 days with no apparent trauma nor any observed effect on behavior or feeding [2]. We will tag each turtle with VHF radio transmitters and use a VHF receiver/antenna to track females and monitor whether individuals emerge to nest during the mass nesting event. After the conclusion of the experiment, we will relocate and recapture all tagged turtles to retrieve equipment and replicate the experiment as needed. Pop-up links and floats will act as backup mechanisms for the retrieval of tags.

We will analyze the tracks and timing of nesting between the experimental and control groups based on data retrieved from the VHF receiver. This will allow us to determine whether the temporary loss of olfaction causes a delay in nesting, which would suggest olfaction is involved in the mechanism for mass nesting.

Note: All of the above methodology has been approved and permitted by Costa Rica (ACT-OR-DR-048-15) and the Institutional Animal Care and Use Committee of UNC-Chapel Hill (IACUC 15-220.0-A).

Challenges

Based on our pilot experiment (featured in our video), the primary challenge of our project is tracking sea turtles amongst the hundreds of thousands that emerge to nest. We will rent a VHF radio receiver, antenna, and transmitter first in order to test the equipment at our field site and ensure we purchase the proper equipment to successfully track individuals. While the receiver will ensure we detect a turtle that comes up to nest, it may still be difficult for us to relocate turtles in the water in order to retrieve transmitters. For this reason, we will use pop-up links and floats as backup mechanisms for the retrieval of tags.

Pre Analysis Plan

We will analyze the tracks and timing of nesting between the experimental and control groups based on data retrieved from the VHF receiver. This will allow us to determine whether the temporary loss of olfaction causes a delay in nesting, which would suggest olfaction is involved in the mechanism for mass nesting. If olfactory cues are involved with the synchronization of nesting, we would expect the sea turtles treated with ZnSO4 to lag behind in nesting.

If there is a lot of variance in our gathered data, we will replicate this experiment, reusing the radio transmitters that we retrieved to increase our sample size and increase the power of our analysis. Our "added value" budget will also allow us to purchase more transmitters to maximize the sample size of our initial experiment.