It’s easy to think of bottlenose dolphins as sleek ocean-dwelling marine mammals, but a researcher at the University of North Florida has determined about 300 dolphins lives their entire lives in the St. Johns River between Mayport and Downtown.
Quincy Gibson was the guest speaker Monday at the Rotary Club of Jacksonville. She is a coastal behavior biologist at UNF and has studied the local dolphins for more than two years.
Gibson said the research indicates that in addition to the year-round resident population, about 200 additional dolphins migrate for a few months each year to the St. Johns River and there is yet another group of transient dolphins.
“They are just passing through,” Gibson said.
Before joining UNF’s faculty in December 2010, Gibson was director of research for the Pacific Whale Foundation and studied humpback whales.
Dolphins are the most common marine mammals in North Florida and are very similar to humans when it comes to behavior, she said. Dolphins have a lifespan of 30-50 years in the wild and a dolphin born at Marineland is more than 60 years old.
Gibson said the dolphin’s life trajectory is similar to a human’s. Dolphins begin mating and reproducing in their teens. After giving birth, females nurse their calves for about three years and then the calf separates from its mother.
Gibson and her team of students track dolphin families and study how young dolphins form relationships with their parents, siblings and other dolphins.
One common misconception is that dolphins always travel with the same group.
“Dolphins are socially complex and have the same social system as we do. They form groups based on what they are doing, like hunting or looking for a mate,” Gibson said.
The northern section of the St. Johns River “is a goldmine for dolphin research,” she said. Part of her focus is on working with the U.S. Army Corps of Engineers to ensure that proposed dredging in the river will affect the dolphin population as little as possible.
Gibson said it would be better for the dolphins if dredging could be conducted in winter months, when there are fewer dolphins in the river and they aren’t calving.
“We are working to collect as much population data as we can before the dredging projects begin,” she said.
One of the major threats to dolphins in the St. Johns River is entanglement. Dolphins can become wrapped in discarded fishing line or crab traps. Gibson said several dolphins are wrapped in fishing line. Researchers attempt to capture and free them, but it’s a difficult job because it’s hard to capture a dolphin with a net in the St. Johns River’s swift currents.
Chemical and noise pollution are other issues affecting the dolphin population.
Dolphins rely on their hearing to communicate and hunt for food. The St. Johns River is becoming less polluted, but toxins still can be harmful to the dolphin population,” said Gibson.
St. Johns River dolphins exhibit a behavior that Gibson said has only been observed here. Local fishermen report observing dolphins tossing fish through the air as well as finding dolphin teeth marks on fish that are caught.
“We call it ‘flounder tossing.’ It’s like they are playing with a Frisbee,” Gibson said.
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