A shoal/school of sardines fish can be 6 kilometers long 3 kilometers wide and 100 feet deep. This fish school will have upto 2,000,000,000 sardine fishes.
A blue whale will eat 3000 to 30,000 sardines in one gulp/mouthful. A huge Sardines school gets attacked by upto 30,000 dolphins, hundreds of seals, thousands of sea birds, hundreds of sharks, many species of whales, whale sharks which is known as feeding frenzy at sea. Many Sardines shoals disappear after a single feeding frenzy.