Sponge-Carrying Dolphins

You don’t need Wikipedia to know that “Dolphins are among the most intelligent animals, and their often friendly appearance and seemingly playful attitude have made them popular in human culture.” (Well, maybe you do…)

Scientists published an article last week in PLoS ONE about dolphin smarts and tool use:  some bottlenose dolphins grab sponges from the seafloor. These dolphins don’t use the sponges for scrubbing dishes or cleaning up, but rather, for hunting and protection. From the abstract:

In the only known case of tool use in free-ranging cetaceans, a subset of bottlenose dolphins (Tursiops sp)…  habitually employs marine basket sponge tools to locate and ferret prey from the seafloor. While it is clear that sponges protect dolphins' rostra while searching for prey, it is still not known why dolphins probe the substrate at all instead of merely echolocating for buried prey as documented at other sites.

A previous study, also reported in PLoS ONE, described the sponge-tool-users as mostly female. Mothers appear to pass the skill along to their daughters, finding and eating fish that most other dolphins (and human fishermen) miss.

Each research team studied dolphins hunting for bottom-dwelling fish, such as barred sandperch, in Shark Bay, Western Australia. Science NOW reports that these fish

don't have swim bladders and so are harder to find with [the dolphin’s natural] echolocation.

The scientists reporting in the more recent study developed a theory why the dolphins go to all this work with the sponges. Discover’s 80beats blog sums it up quite simply:

They’re after fatty, energy-rich fish on the seafloor, and the sponges let them scare up a snack without scraping their beaks on sharp rocks or coral.

Time to update that Wikipedia page!

Image: Ewa Krzyszczyk