How does schooling protect anchovies and sardines from predators?

Schooling provides a vital defensive behavior for clupeiform fish like anchovies and sardines by enhancing individual safety through collective action.12

When threatened by a predator, these fish utilize several strategies to avoid capture:

• Formation Contraction: Anchovies, which may be spread over hundreds of meters, rapidly contract into a tight, moving, and writhing sphere only a few meters across when a predator approaches.12
• Predator Confusion: By milling around in compact balls, the school prevents a predator from focusing on or isolating a single individual. This inability to target one fish often frustrates the predator’s hunting attempt.21
• Dilution Effect: Living in large groups reduces the statistical probability of any single individual being consumed. Because a predator can typically only capture one prey item at a time, the risk to each fish is significantly lower than if it were living solitarily.3
• Safety in Numbers: The school acts as a single, large organism, which may deter predators or provide a better chance of survival against various environmental hazards.12