Spinner dolphins have long been known for their teamwork in capturing prey but a new study using high-tech acoustics has found that their synchronization is even more complex than scientists realised and likely evolved as a strategy to maximize their energy intake.

The study found that dolphins engage in a highly choreographed night-time "dance" to enclose their prey, and then dart into the circle of confused fish in organised pairs to feed for about 15 seconds, before backing out and letting the next pairs in line take their turn. The feeding would last for about five minutes, during which time each dolphin got two opportunities to feed, and then the group rose as one to the surface to breathe, maintaining their circle. The dolphins would take one breath and then dive down and begin the process anew. The study is important because it greatly expands knowledge of spinner dolphin behaviour and much of the knowledge so far about spinner dolphin feeding has been anecdotal because they are primarily nocturnal in their feeding. However, acoustical eavesdropping allowed the scientists to "view" the dolphins' behaviour without interrupting their routine with lights and underwater cameras.

This new study also revealed that the group of dolphins never broke their circle and always surfaced together so the question is how were they communicating with each other, and how do they pass on that knowledge to their young? Dolphins are often vocal and their use of frequency-modulated whistles was thought by many to cue their coordinated behaviour but the researchers found they didn't use those whistles at all while hunting prey – just during non-foraging times or when they were actually surfacing. Instead, they used a series of "clicks," with the highest click rates taking place just prior to foraging.

Spinner dolphins are found primarily in tropical and subtropical waters, offshore and near island chains. They grow to a length of about six to seven feet, and feed on small, deep-ocean prey including lanternfish, shrimp and juvenile squid. During their hunting forays, these athletic, acrobatic dolphins catch and consume a single fish at a time and each lanternfish may only be 3-5 inches long. To match their 3,200-calorie-per-day diet, they need to eat at least 650 fish each night – plus enough extra to fuel the energy they burn during the hunt, perhaps another 200 to 300 fish. That’s a lot of fish!

Results of the study were recently published in the journal, Acoustical Society of America.

Image: oregonstate.edu