Selectively save only desirable species or size classes. Treatment of several much smaller, but representative sections can provide a subsample from which to estimate the whole population. Kills smaller fish, particularly bluegills. Drawdown of a lake or pond will have a dramatic effect on the fish community. Fish are crowded into a smaller area, usually away from cover.
Small fish become more vulnerable to predation by larger fish and tend to be reduced.
Predators may fatten up and store energy for subsequent spawning. When the water level is brought back up, the fish are relieved from crowding and usually display good reproduction and rapid growth. Water level manipulation can either permit excellent reproduction or prohibit reproduction depending on timing and speed. Their normal habitat is a pulse-stabilized system. Lateral lakes along the Mississippi were famous around the world for bass fishing until the Army Corp stabilized the river.