Video: Sailfish ‘slasher film’ sheds light on evolution of group hunting

Once a year for 5 years, a crew of researchers would set sail off the coast of Cancun, Mexico, to locate frigate birds flocking and diving just above the ocean’s surface. The scientists weren’t actually interested in the birds—the animals merely served as a smoke signal for the mayhem unfolding below: sailfish ganging up on sardine schools. Sailfish hunting groups range in size from four to as many as 70, but their strategy is rather simplistic. Unlike chimpanzees, they don’t assume special roles, like cornering the prey while others look on as chimps do, and their attacks aren’t really coordinated, meaning they don’t plan their strikes based on the location of others in the group. It does, however, appear that the sailfish time their attacks: One at a time, they charge the school—rather slowly considering the high speeds they are able to reach—and use their bill, which is covered in microteeth, to rapidly slash and prod the sardines. Then they take a rest. Only 24% of attacks end in a tasty sardine snack, but 95% end in an injury to the prey, the team reports today in the Proceedings of the Royal Society B. This process ends up pummeling the school back and forth, likely causing the sardines physiological distress as well. Injured or disoriented sardines are easier to catch. Though the sailfish actually might not catch as much prey as they would hunting alone, they certainly don’t need to work as hard for it. If this energy-saving technique benefits sailfish in the long run, researchers say this could be an example of behavior that leads to more complex cooperative strategies seen in other group living animals.