Why do sardines swim in such large groups?

Sardines swim in large groups, known as schools, primarily for protection against predators. By forming a dense, cohesive mass, they increase their chances of survival through confusion tactics, making it harder for predators to target individual fish. Additionally, schooling enhances foraging efficiency, as it allows sardines to locate food sources more effectively through collective movement. This social behavior also aids in maintaining optimal hydrodynamics, reducing energy expenditure while swimming.