Barometric pressure is a measure of atmospheric pressure, also called air pressure, that is often indicated as "inches of mercury" on a barometer. Less air above the barometer means lower pressure, and more air means higher pressure. Air pressure presses down on water, but can it be felt by fish? Fish cannot predict changes in barometric pressure, but do they react to changes in air pressure?
Many fishermen believe good or poor fishing can be determined by the level of barometric pressure.
At any given time, barometric pressure is either stable or is rising or falling. Fish react differently to both stable and changing barometric pressures.
Changing barometric pressure stirs up fish in their habitat by changing the buoyancy of low-level food items such as plankton. Small fish follow the plankton, larger fish follow the smaller fish.
Compared with changes in hydrostatic pressure---water pressure up or down within the water column---barometric pressure changes are very slight and not likely to be felt directly by the fish.
Experts say fish likely are not reacting to barometric pressure changes but rather the effects of weather on the water. Weather following a change in barometric pressure can change light levels, water temperature and other factors affecting fish behavior. Fisheries biologist and tournament angler Roger Hugill says, "An extended period of stable weather allows fish to find their comfort zone---a balance of the right water temperature, oxygen, light penetration and other factors---and fuels a nice, steady bite."
