In 2013, 52 of approximately 100 Atlantic spotted dolphins left their home in the shallow waters of Little Bahama Bank (LBB) off Grand Bahama Island, travelled 100 miles south and relocated to a new island, Bimini. For at least 30 years, the spotted dolphins lived on LBB. No one could have ever guessed that one day they would just be gone. But that’s exactly what happened. And Bimini was already home to an existing resident population of both spotted and bottlenose dolphins. We wondered: What will happen next, and will it happen again?

I, and other biologists who work with the Wild Dolphin Project (WDP), led by founder and research director Denise Herzing, PhD, suspect that the dolphins left to find new food sources due to a crash in the food web on LBB. Leading up to the exodus, we found that chlorophyll levels dropped in the region. Chlorophyll is a pigment produced by microscopic marine algae, called phytoplankton. Scientists can monitor chlorophyll levels to determine the health of an ecosystem since phytoplankton is at the base of the food web, providing sustenance for shrimp, snails, and jellyfish. If phytoplankton levels drop, everything else will drop too, including the numbers of flying fish and squid that spotted dolphins rely on. 

After the initial migration event in 2013, we spent the next several field seasons monitoring both locations and learning about the resident dolphins who already lived off the island of Bimini on Grand Bahama Bank (GBB). I remember the first time entering the water with the Bimini dolphins. They were seemingly so familiar in appearance, but there was no question that these individuals were total strangers. We didn’t know them, and they didn’t know us, unlike the dolphins off Grand Bahama who would come leaping excitedly to the bow of our research vessel to catch a ride. The Bimini dolphins sounded different, too. I heard them make barking sounds that I had never heard the spotted dolphins from LBB make. “It’s likely that the dolphins do have different dialects. This has been found in many other areas,” Herzing said. 

We wanted to find out what would happen when the two groups encountered each other. Would they fight over food or befriend each other for increased mating opportunities? “I had no idea what they would do,” said Herzing. “I was primarily concerned that they would be competing for food resources.” To determine how the move impacted social structure, researchers from the WDP analysed the dolphin relationships after the move, led by Cindy Elliser, PhD, a research associate with WDP and researcher director and founder of Pacific Mammal Foundation. From 2013 to 2020, WDP recorded a total of 206 dolphin encounters off Bimini and collected data that included individuals present and behaviours such as fighting, playing, mating, feeding and travelling. Sometimes, groups were made up of only the resident Bimini individuals, while other times, the groups included solely the immigrants from Grand Bahama.