Image courtesy of Ramon Llaneza

From: Claudia Llaneza
Boynton Beach, Florida, USA, June 27, 2008

Understanding Shark Behavior

Our journey to the Bahamas began on Saturday June 21st. We departed from Boynton Beach Inlet, on the East Coast of Florida, in spite of the weather forecast that predicted scattered showers and thunderstorms. Our plan on this trip is to study short-term changes in the behavior of reef sharks (Carcharhinus perezii) and bull sharks (Carcharhinus leucas). My father, who is a marine biologist, uses these scientific names for the sharks. Our team will observe behavioral changes after the sharks are stimulated by sensors.

Our mission on this first dive was to study bull shark behavior. We descended to a depth of about 90 feet, where we saw a green eel, a school of grouper, a turtle, and other creatures of the ocean. Approximately thirty minutes into the dive, lightning illuminated the sights surrounding us. At that time, I began to run out of air so I signaled to my dad, and we began to ascend to the surface. We finally reached the surface, and to our surprise the boat was no where to be found. We realized that a storm had suddenly developed and the sky was filled with dark gray clouds.

We floated for about five minutes until the boat emerged from the storm. We signaled it to come towards us but it did not move. That's when we realized something was very wrong. We decided to swim towards the boat, not knowing that the boat had been struck by lightning and was unable to move. We swam for about ten minutes when we all realized we had “company." As I stuck my head in the water, I noticed a bull shark emerging from the deep waters, and before I knew it five sharks were surrounding us. As we continued swimming towards the boat the sharks followed closely behind! They then began to display aggressive behavior, making rough turns and swimming faster around us. My dad reminded us to swim calmly because this kind of shark behavior was just a response to our movements and the vibrations we were causing while swimming.

Sharks can hear sounds and are attracted to the rapid and irregular, low frequency sounds produced by us while swimming. These movements cause almost the same vibrations and sounds produced by a struggling or injured fish. After swimming around us, the sharks eventually realized that we were not their natural prey and left us alone. As soon as we reached the boat my brother explained that lightning had struck the antenna on top of the boat, shutting off the motors and the electricity. We waited on the boat until we were towed back to our dock. Even though this was a major setback in our plans, our boat is being repaired and we are getting ready to return to our research on Monday, June 30th 2008.

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Postcards from the Field: Shark Watching

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