Fish beware: Bottlenosed dolphins may be able to pick up your heartbeat

To snap up fish, bottlenosed dolphins may rely on more than just sharp sight and sonar detection. The creatures might also pick up on the weak electric pulses prey produce each time their hearts beat or air filters through their gills.

In a new experiment, two bottlenosed dolphins named Dolly and Donna reliably sensed faint electric fields on the scale of microvolts, says Tim Hüttner, a sensory biologist formerly affiliated with the University of Rostock in Germany. That puts the marine mammals’ Spidey sense on par with the Guiana dolphin (Sotalia guianensis) and some egg-laying mammals like platypuses.

The ability to detect the electrical signals living things give off is called electroreception. It has been previously documented in fish, amphibians and sharks (SN: 6/27/16). But it was only in 2011 that the Guiana dolphin made the list, as researchers discovered telltale sensory receptors hidden in an organ on the animals’ snouts (SN: 7/27/11).

In 2022, Hüttner and his colleagues  identified the same structure in bottlenosed dolphins and confirmed that the creatures could detect electric fields on the scale of 0.5 millivolts per centimeter (or 500 microvolts), similar to those that some large fish and crustaceans emit. The new finding suggests that common bottlenosed dolphins (Tursiops truncatus) can likely make out the much subtler signals emanating off the majority of fish, the team reports November 30 in the Journal of Experimental Biology.

For the new study, the researchers trained Dolly and Donna to position their snouts in a metal apparatus and to swim away if they could sense an electrical impulse delivered to their sensory organs. The dolphins proved sensitive to both direct current and alternating current, two forms of electricity that living things generate. The dolphins excelled, however, at detecting direct current, which produces a steady signal. Donna picked up on fields as low as 5.5 microvolts and Dolly on those of 2.4 microvolts.

The study provides solid evidence for an intriguing theory, says Paul Nachtigall, a marine biologist at the University of Hawaii at Manoa. Scientists have long regarded dolphins’ sensory organs, pits on their snouts, which prior to birth carried whiskers, as vestigial structures. It’s plausible that the organs may have evolved to fit another purpose, he says.

Electroreception may come in handy in situations where sight and echolocation are impaired. For instance, Guiana dolphins are benthic feeders, primarily hunting for food on the seafloor, where the sediment can muck up their senses.

Bottlenosed dolphins don’t hunt the same way but do often reside in murky waters and occasionally stick their heads into the sand to look for fish, in a hunting method called crater feeding. Echolocation stops working close up, but electroreception allows dolphins to spot prey a few centimeters away. The ability may just give the creatures the last push they need to nail a target, Hüttner says.

To test this idea, the team would like to study the dolphins’ electroreception while they are moving, Hüttner says.  

Other species of dolphins have pits on their snouts as well, raising the possibility that electroreception is more widespread, he notes. Given that these creatures adopt different hunting strategies, the ability may serve an additional function: helping dolphins to orient themselves along Earth’s magnetic field lines as they migrate.

“There’s just so much to find out,” Nachtigall says. “This study is just the first page of a book.”