Alum Spotlight: Celebrating Captivating Sea Creatures

It’s April 14, which means it’s National Dolphin Day — an occasion to highlight and educate about these iconic and familiar marine mammals.

While some people may think dolphins are always happy due to their friendly appearance, they have a darker side — something scientists with the Wild Dolphin Project (WDP), the world’s longest running underwater study of dolphins, know all about.

In a new study recently published in the journal Animal Behavior and Cognition, lead author and Florida Atlantic University (FAU) alumna Cassie Volker of WDP explored the aggressive fights between the males of two species of dolphins that coexist in the Bahamas.

“People have the misconception that dolphins are cute and cuddly because of how they are portrayed in movies and in captivity,” Volker said. “But dolphins are very intelligent, social mammals who live complex lives. They are skilled hunters, they recognize individuals within their groups, and they even have preferences on who they associate with.”

Based in Jupiter, the Wild Dolphin Project was founded in 1985 by Denise Herzing, Ph.D., an affiliate professor in the FAU Charles E. Schmidt College of Science, to study the behavior and communication of two species of dolphins in the Bahamas, the Atlantic spotted dolphin and the bottlenose dolphin. Since then, Herzing, who also serves as the research director of WDP, and other scientists with the project have studied everything from social structure and habitat use to genetics and of course, aggression between males.

Along with Herzing as her coauthor, Volker's goal for this study was to determine if spotted dolphins altered their aggressive behaviors based on their opponents, in this case, when they fought those of their own species versus when they fought bottlenose dolphins, which are about a third larger in size.

When fighting, spotted dolphins have a variety of behaviors in their repertoire, like head-to-head posturing, open mouth displays, tail and jaw smacking, body charging, bubble displays and the pinning of an individual on the seafloor.

Volker sleuthed through 13 years of archival underwater video encounters from WDP’s long-term database to find footage of aggression. She analyzed 22 video clips, totaling more than 180 minutes.

Volker said that it’s “thrilling to watch the drama unfold during these intense encounters,” both in the wild and in the video clips. “Of course, you're worried for the dolphin who is the target of the aggression because you don't want any serious injuries to occur, but the good news is, the aggression we have observed isn’t deadly.” In more than 35 years, WDP has never seen a death as the result of an aggressive encounter. “But, some of the behaviors sure do look painful,” she added.

The scientists found that when the smaller spotted dolphins fought the larger bottlenose dolphins, they tended to use behaviors that required more energy, such as chasing. But when the spotteds fought each other, they used display behaviors like open-mouths, rather than biting or chasing. “As the smaller species, spotted dolphins have more to lose in a fight with the bottlenose dolphins. So having strong signals, even if they are risky, probably sends a clearer message,” Herzing said.

For these two species, aggression is an important part of their relationship, something that Herzing calls surprising. “These two species travel together, play together, mate sometimes, so the fact that they also fight tells us that they have a complicated relationship. This study really showed that it is necessary, when communicating with another species, that signals may need to be overt to get through,” she said. “Even in the case of two dolphin species that have similar physical features, their cultures are likely different enough to warrant emphasized signals in their interspecific communication.”