Facts Require Confirmation....Beliefs Thrive Without Confirmation
Barometric pressure is not without merit but its relationship to fish behavior is widely misconceived.
The association between atmospheric pressure and fish disposition is coincidental, it is not causal.
Additionally, barometric pressure is a lagging indicator, like driving your car while looking in the rear-view mirror.
Water Pressure versus Air Pressure
Air is a highly 'compressible' medium, whereas water is virtually 'incompressible'. Changes in barometric pressure
are barely perceptible to fish. As an example of Air versus Water, imagine pressing an air-filled balloon
against a rock and expecting a reaction from the rock. To further display the power of water pressure,
allow me relate a graphic but real-world example. In saltwater, we often fished for ling (red hake) and whiting (silver hake)
at the Ambrose Lightship where water depths exceed 100 feet. Fish that were hauled topside were subjected to
a lethal plunge in water pressure. Due to a dramatic reduction in water pressure their eyes were bulging
out of their sockets and their gullet was in their mouth and turned inside-out.
Needless to say, catch-and-release was not an option.
A Little Science Goes A Long Way
All matter has weight, even gaseous matter such as the earth's atmosphere. Air is extremely light
but the earth's atmosphere is several hundred miles high, so at sea level our atmosphere exerts 14.7 pounds
of pressure per square inch. Barometric pressure (atmospheric pressure) is usually quantified by the height
that a column of mercury rises in a standardized tube. At sea level, normal barometric pressure will force mercury
29.92 inches up the tube, which is expressed as 29.92 inHg or 'one atmosphere'. Okay, now we have
a Barometric Baseline, so let's add some meteorological events. During an average cold-front
(high-pressure clockwise cell) the barometric pressure will climb to around 30.32 InHg, a mean rise of 1-1/3%
on balance. During an average warm-front (low-pressure counterclockwise cell) the barometric pressure
usually falls to around 29.52 inHg, a drop averaging 1-1/3% below normal.
In contrast to air, water has a far greater specific gravity. At a depth of 34 feet, water exerts the same
pressure per square inch (lb PSI) as several hundred miles of atmosphere. So at 34 ft deep, the sum
of air pressure and water pressure is 29.4 lb PSI or 'two atmospheres'. Due to water's high specific weight,
when a fish swims just 5.4 inches downward in the water column, the rise in pressure is identical to an average
high-pressure system (cold front). Inversely, when the same fish swims 5.4 inches higher in the water column,
the drop in pressure is equivalent to an average low-pressure cell (warm front). For anyone interested in calculating
their own formulas & results, I've included two useful constants:
=> 1-foot column of water = 0.433 lb / sq. in.
=> 1-foot cube of water = 62.35 lb
COINCIDENTAL FACTORS
In and of itself, barometric pressure exerts no influence on fish behavior, however it frequently accompanies
meteorological conditions that do. In any case, there's no advantage to monitoring a proxy like atmospheric pressure,
when the direct causes are more obvious and more timely. Atmospheric pressure is not only a symptomatic indicator
but often a laggard indicator. Listed below are easily recognized weather conditions that directly affect the behavior
and disposition of fish, regardless of barometric pressure:
APPROACHING COLD FRONT
> Falling Barometer
Until the cold front is actually upon you, the barometer will likely continue to creep lower
> Building Cloud Cover
Reduced light level is positive for fishing, with or without a falling barometer
> Increasing Winds
Wind creates surface refraction that reduces luminosity and also aggregates plankton
which are both positive conditions, with or without a falling barometer
> Steady Air Temperatures
Stable weather over the long-term is very positive to fishing.
but over the short-term, steady air temperatures have no appreciable effect
PASSING COLD FRONT
> Rising Barometer
By this time, increased winds & falling air temperatures have spilled the beans
> Clearing Cloud Cover
Increased light levels are negative for fishing, with or without a rising barometer
> Gusty Winds
Early on, gusty winds are not negative, but persistent cold northwest air mixed into the epilimnion
eventually becomes negative. Barometric pressure offers no input as to the pivot point in timing.
> Falling Air Temperatures
Falling air temperatures is one of the most negative events in bass fishing,
especially for Florida-strain bass. Once again, barometric pressure offers no useful input
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APPROACHING WARM FRONT
The four conditions noted above under 'Approaching Cold Front' also apply to an 'Approaching Warm Front'.
In other words, the barometer cannot differentiate between an approaching warm front and an approaching
cold front (ouch). On the other hand, 'wind direction' quickly and accurately distinguishes an approaching
warm-front from an approaching cold-front.
Roger
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