Barometric Pressure and Fishing: Fact or Myth

I am a fishing enthusiast and it is something I can’t deny. A couple of years back I used to actively wrote articles about sport fishing and its phenomena in our state. Some of it were published in the local newspaper and lots of them were published online and shared though out fishing forums. Being a fishing enthusiast myself, I can’t help finding new ways and gather new information on how weather around us effect the fish’s feeding activity and behavior. One of the thing I learnt was how barometric pressure or air pressure effect fish behavior. The point was, when there was a drop or increase in the air pressure, you must know when to go fish or throw your bait.

Understanding Barometric Pressure / Air Pressure

Before we go further into details on how and does barometric pressure effect fish behavior, we need to first have at least some basic knowledge on what is barometric pressure.

Pressure, whether in the air or in the ocean, is expressed by scientists as units of “atmosphere.” One atmosphere is defined as the pressure caused by the weight of all the overlying air at sea level. Atmospheric pressure is often called barometric pressure because it can be measured by the height of the mercury column in a barometer. Changes in barometric pressure, therefore, indicate capricious weather. In general, low-pressure systems bring unstable conditions, often with precipitation and clouds. A rising barometer means high-pressure is approaching, the harbinger of stable and clear skies. On a given plane, low-pressure areas have less atmospheric mass above their location, whereas high-pressure areas have more atmospheric mass above their location. Likewise, as elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation.

Air Pressure and Height Relativity.

Air Pressure and Height Relativity.

Average sea-level pressure is 101.325 kPa (1013.25 mbar, or hPa) or 29.92 inches (inHg) or 760 millimetres of mercury (mmHg). In aviation weather reports (METAR), QNH is transmitted around the world in millibars or hectopascals (1 millibar = 1 hectopascal).

Underwater Barometric Pressure

How much do fish respond to these day-to-day fluctuations? Consider that a normal value for barometric pressure is about 30 inches. Strong high pressure is about 30.70 inches. A powerful low, such as during a hurricane, can reach down to 28 inches or less. The difference between these two extremes (2.7 inches of barometric pressure) is equal to about .09 atmospheres. The rate of a falling barometer also tells us how fast a low-pressure storm is approaching. A slow-moving storm would have a dip of about .02 to .03 inches of barometric pressure per hour; a fast-moving storm will drop the barometer about 0.05 to 0.06 inches per hour.

Pressure in the ocean, called hydrostatic pressure, increases with depth due to the weight of the overlying water. Water is almost 800 times denser than air. Thus, hydrostatic pressure increases much more rapidly than atmospheric pressure. If you swim or dive just a few feet below the water’s surface, you feel this rapid increase in pressure.

Simply said, barometric pressure does not change quickly enough to magically turn the bite on or off. The rate and amount of change in barometric pressure is insignificant compared to what’s going on below the surface.

Hydrostatic Pressure and Fish Activity

Hydrostatic Pressure and Fish Activity

Hydrostatic Pressure

At a depth of just 32.8 feet in the ocean, the hydrostatic pressure is equal to the pressure from the entire weight of the earth’s atmosphere as measured in pounds per square inch. In other words, at 32.8 feet, the total pressure, due to the weight of both the atmosphere and the water, is two atmospheres. At 65.6 feet it’s 3 atmospheres, and so on and so forth.

Fish can tolerate hydrostatic pressure because they have a swim bladder containing a volume of gas, which they adjust to equal their environment. This enables most fish to comfortably make small and quick up or down movements in the water column.

In the ocean, four main factors can change the hydrostatic pressure in the fish’s world:

  1. Natural air bladder adjustment
  2. Tides
  3. Waves
  4. Weight of the air (but quite a gradual effect)

When compared to the effects of the tide, waves, and normal movements of the fish in the water column, changes in hydrostatic pressure caused by barometric-pressure are trivial for saltwater fish. Even a dramatic change in the barometer will be lost to the everyday pressure changes experienced by fish under normal oceanographic conditions.

Conclusion

So, my friends. Always remember that observing the mercury column of your everyday Barometer and smile to yoursefl, Yes! it is a good day to fish…or going to work is not really that bad if you think about it in a positive way, but it’s unlikely that barometric pressure alone can trigger the sudden bite that angling’s common wisdom often asserts.

Truth to be told, I was fooled by this myth some times ago that made me bought a Casio Twin Sensor (Baro & Altimeter) so that I know when is the right time to go fishing, but on the bright side, now I know that barometric pressure does not effect fish behavior but I can monitor if the weather is good and safe to go out fishing and doing other outdoor activities.

Happy Fishing!

Source:

  1. Dr. David Ross, 2004.  The Fisherman’s Ocean (Stackpole Books). Woods Hole Oceanographic Institution.
  2. International Civil Aviation Organization, Manual of the ICAO Standard Atmosphere, Doc 7488-CD, Third Edition, 1993, ISBN 92-9194-004-6
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