Some ecological consequences of fish school volumes

SUMMARY. Two consequences of a recently published method of calculating fish school volumes are examined in the light of ecological population data. First, minnow and roach schools occupy only about 0.01% of the volume of water in which they live, graphically illustrating the vagaries of field sampling, and providing reference values for foraging studies. Secondly, I show that roach schools in one river are constantly within attack range of pike predators. If this situation is general, theories which assume that schools function strategically merely to reduce the probability of encountering a predator, break down, whereas my predictions suggest that there is strong selection for direct predator evasion tactics in schools.