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THE HIGHS AND LOWS OF BAROMETRIC PRESSURE

Barometric pressure has a major influence on fish behavior which can give the angler an advantage and general idea of what they can expect out of a day of fishing.
By Tony Salerno
Tags: inshore, offshore, freshwater, surf
THE HIGHS AND LOWS OF BAROMETRIC PRESSURE
A falling barometer associated with a low pressure system is known to trigger a good striped bass bite.

Most veteran anglers in the know will make Mother Nature their first consideration when planning a day on the water. This is particularly true when heading off into the Big Pond. Most savvy anglers are also aware that tides, temperature, and lunar phases are also key factors towards a day of success. The truth is you cannot equate all these factors without atmospheric pressure, better known as barometric pressure, which not only impacts our weather, but also has a major influence on fish behavior which can give the angler an advantage and general idea of what they can expect out of a day of fishing. And while predictions are just that, we can unlock some of the mysteries determining when the bite should be on or off.

Simply, barometric pressure is nothing more than a measurement of pressure, which is nothing more than the weight of air over a certain point, which in this case is sea level. It is instrumental in weather observations, since its fluctuation indicates the movement of weather fronts and systems. Barometers consisting of liquid mercury (Hg) are commonly used to measure the surface air pressure. A mercury barometer is a glass tube with mercury that has been placed upside down in a container of mercury. Any change in pressure causes the mercury in the tube to either rise or fall. For example, when the air pressure rises, it pushes the mercury higher. When the air pressure drops, so does the mercury level. The mercury is measured in units known as millibars (mbs) or inches of mercury (Hg.) At sea level, a normal barometer reading is 30 inches (Hg.) If a relatively strong high-pressure system was to move into an area, the barometer would read between 30.50 and 30.70 inches. Conversely, if a strong low-pressure system were to move in, the barometer could dip as low as 27.25 inches of mercury. The greater the difference in air pressures between the two competing systems, the greater the wind. Just the same, the greater the surface area covered by low pressure, the greater the size of the area of wind. Under high pressure, weather is typically fair, with sunny skies. Conversely, low pressure means precipitation, wind, and inclement weather. A barometer reading of 28 inches or lower is typically associated with strong gusty winds from the east and northeast. When the pressure drops below 28 inches, then you are looking at anything from an old classic nor'easter, to a potential hurricane.

EFFECT ON FISH
There are no definitive answers on how a rising or falling barometer affects fish. In fact, this is one influence that marine biologists and ichthyologists have studied least. However, most marine biologists and ichthyologists do agree that fish sense pressure changes through their air bladders. Most also believe that fish without air bladders sense pressure change through their lateral lines. The lateral line system found in many fishes is the sensory unit of the species, which is sensitive to the difference in water pressure. Even a minor barometric pressure change affects a fish's swim bladder.

The general theories are that when the barometric pressure rises, it exerts pressure upon the bladder, thus affecting their behavior and appetite.

The general theories are that when the barometric pressure rises, it exerts pressure upon the bladder, thus affecting their behavior and appetite. When the barometric pressure is dropping, there is less pressure on the fish's bladder, which means there is less pressure squeezing on the bladder, causing it to expand. When their bladders expand, fish feel the discomfort and don't concern themselves with feeding as much. When the barometric pressure is steady and holding at around 30.00 inches for at least 24 to 48 hours, either after a high or low-pressure system has passed, the fish become stabilized and begin feeding aggressively. During this period, the weather is usually fair, winds are light, and may remain that way for several days, or until the next low pressure system moves into the area. Just before a low-pressure system is about to move into an area, the fish can sense that the barometer is about to drop. Since they know that it won't be long before their bellies will begin to ache, they will often go on an intense feeding binge until the pressure drops.

Assuming the theory that fish sense pressure changes with their swim bladders is correct, it must be noted that different species of fish have different size bladders. Therefore, each species will sense barometric pressure differently, which may be why some fish will shut down, while others may bite under the same conditions. True or not, there is no doubt in my mind that barometric pressure has a dramatic influence on fish. However, rather than wasting space trying to figure out the scientific concept behind the theory, allow me to explain my approach that keeps me in the action under most weather conditions year after year.


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