Sardines form a tight group in the presence of predators. This is believed to be a protective mechanism that sacrifices some of the group to a predator but protects the others. The group of fish also changes direction rapidly and repeatedly, which confuses the predators. These behaviors may not be beneficial in the South African sardine run, however, because multiple predators surround the fish and they are herded into a tight ball that can’t escape.
The evolution of sardines is an exciting topic. Some of the details are known, but scientists still debate others. A complete article would be required to describe the evolution of the fish and the different theories related to the topic.