Mystery of Dolphin Tool Use Solved by GU Researchers
July 20, 2011 – Wild dolphins use marine sponges as tools to find food they cannot easily detect through echolocation, according to a new study published by Georgetown researchers in the July 20 issue of the online journal PLoS ONE.
Georgetown’s Eric Patterson (G’12), a Ph.D. in biology candidate, and longtime dolphin researcher and professor Janet Mann published the study 26 years after the discovery that dolphins use tools to forage for prey. The study was funded by the National Science Foundation, the National Geographic Society and Georgetown University.
“Tool-use has long fascinated us, especially since we are the quintessential tool-users and it was once believed to be a hallmark of humankind,” Patterson explains. “But some primates, elephants, birds and other species also use tools, and studying why and how they do so provides insight into the context in which tool-use arises.”
Most wild animals that use tools do so to extract food from difficult to reach places and Shark Bay bottlenose dolphins in Western Australia are no exception.
“These dolphins rip up marine basket sponges that grow along the seafloor and then wear them for protection when scouring the rough substrate for prey,” says Mann.
A staple for the sponging dolphins is the barred sandperch, but the mammals cannot detect it through echolocation because the fish lacks a gas-filled organ called a swimbladder.
Most fish have swimbladders, which helps control their buoyancy. Bottlenose dolphins are able to detect the gas chamber through echolocation.
By using the marine sponges to uncover the sandperch, Patterson and Mann show that the dolphins use the sponge tool to easily access the fish without injuring their beaks on the rough seafloor below.
“Sponging dolphins seem to specialize in hunting these swimbladderless prey when compared to the rest of the Shark Bay population,” says Mann, who has been studying the bottlenose dolphins there since 1988.
Patterson says the researchers believe the small size of the prey explains why “spongers are the workaholics of the bay – they have to hunt often in order for this small-yet-reliable meal to be enough, but it seems to work for them since they are able to pass the method down for generations.”
Nearly all of the female Shark Bay dolphins that live in channels that are 7 to 12 meters deep specialize in sponging.
“These clever dolphins have figured out a way to exploit fish that other dolphins cannot,” Mann says. “This highlights the dolphins’ innovative and problem-solving ability, which has been well-demonstrated in captivity, but less so in the wild.”
Like Mother, Like Daughter
Mann also notes that her research team’s previous work has demonstrated that dolphin mothers pass the sponging method down to their daughters and some of their sons. So far, the team has documented three generations of spongers.
“This tradition is highly specific to the micro-habitat spongers live in, demonstrating the importance of ecology in the evolution of tool-use and culture,” she says.