Scientists from Florida Atlantic University’s Harbor Branch Oceanographic Institute in Fort Pierce and Hubbs-SeaWorld Research Institute have revealed surprising new information about bottlenose dolphins in the Indian River Lagoon in a just-published study based on radio tracking research conducted over a three-year period.
In what they call the most comprehensive radio tracking study of dolphins ever conducted in the lagoon, co-authors Dr. Greg O’Corry-Crowe, a Harbor Branch research professor, and Wendy Noke Durden, a Hubbs research scientist based in Melbourne Beach, confirmed that the nine animals they tracked from 2007 to 2010 consider the lagoon their home, seldom if ever venturing out into the open ocean.
No surprise there, the researchers said – earlier Harbor Branch research had found the same thing – but several other behaviors raised eyebrows: The highly-intelligent marine mammals spent a lot of time in waters less than 3 feet deep; they spent 53 percent of their time traveling, but didn’t travel very far, ranging on average only about 17 miles away from their home waters; and, most surprising, the notoriously social animals spent as much as 72 percent of their time alone, interspersed with brief meetings with many other dolphins.
“They do, for the most part, live in the lagoon,” Durden said. “Whatever happens in the lagoon is going to impact them. From what we’ve seen, their ranges are pretty fixed. If they don’t move very much, they are going to be in trouble [if the lagoon becomes more polluted].”
Since the study was conducted, the lagoon has been afflicted with a series of destructive algal blooms fueled by excess nitrogen and phosphorous, seagrass die-offs and fish kills that have periodically disrupted and damaged the lagoon ecosystem during the past eight years.
The scientists and their collaborators collected the newly published dolphin intel by attaching earring-size transmitters to the animals’ dorsal fins and tracking them by boat and aircraft with radio receivers daily or several times a week up and down the 156-mile lagoon. All tracking was conducted in daylight so that the researchers could locate each individual through its unique radio signal and then visually observe and record its behavior.
O’Corry-Crowe said the dolphins observed in very shallow waters were mostly feeding. “They often use these shallow habitats around islands and close to shore. It’s helping them to successfully hunt,” he said.
Both O’Corry-Crowe and Durden emphasized that learning how dolphins spend their time is critical to managing and conserving the species.
“Our finding that shallow water habitats are used extensively by Indian River Lagoon bottlenose dolphins, particularly for foraging, indicates that these habitats are likely critical to their health and fitness,” O’Corry-Crowe said. If those shallow-water habitats are degraded by pollution and ecological changes, it follows that dolphins would likely be harmed.
Other Harbor Branch research has shown that many bottlenose dolphins in the lagoon are already sick, suffering from a variety of diseases.