Barometric Pressure

.ghoti. · September 30, 2010

If you're going to quote specifications, at least get the numbers correct.

1000 millibars is a little less than one standard atmosphere; approx 14.5 psi. I left out a bunch of numbers on the right side of the decimal place.

one foot of water column equals 0.433 psi.

I had to look up some readings for Illinois.

Highest reading ever recorded = 30.99"Hg

Lowest reading recorded = 28.71"Hg

A difference of 2.28"Hg = 77.21mb = 31" water column

A more typical change to see as a front passes is in the range of 10 - 30 millibars, 4 - 12" of water.

John, if you think in terms of absolute pressure, the pressure at any given depth is the sum of the weight of the water above that point, plus, the weight of the air above that.

All of which does nothing to answer the original question.

My own observation is that, more often than not, fishing gets better as the barometer is dropping. And gets worse during a rise. Stable pressure means to look to other factors.

Does this mean bass are responding to an increase in activity in the food chain? Sounds reasonable.

Does it mean they are reacting to a change in light levels? Sounds reasonable.

Wind, current, etc? Sounds reasonable.

All the above? Sounds reasonable.

A different question is, do the bass "feel" the barometric pressure change?

Who knows. The lateral line is a pressure sensitive instrument. Is it sensitive enough to detect these small changes? Who knows. It could very well be.

If that's the case, it could be argued that bass have "learned" that falling pressure means more food will be available for a short period of time, and move to take advantage of it. If we define instinct as learning that occurs over hundreds of thousands of generations, that is.

Fishing Rhino · September 30, 2010

It really doesnt affect the bass directly as much as many think.. But it does affect the food chain. Small zoo plankton are affected. If the pressure is lowering the small zoo plankton become more buoyant and thus easier for small minnows and such to feed on them. Small minnows and such then become more available and then hence the bass. When the pressure is rising and or high the zoo plankton are more stuck int he weeds and on the bottom.

I do agree with what the forage is doing, I just don't think barometric pressure has that much influence on hydrostatic pressure. And that correlation is backwards, anyway. The higher the pressure, then the aquatic creatures would have to move up to compensate. I think it has to do more with light levels, wind and current. A low pressure front moves in, clouds block the sun, there's wind, creating current, and the critters come out, followed by the baitfish, followed by the game fish.

It affects hydrostatic pressure in direct relationship to its rising and falling. When I was a kid, there was a popular toy in a bottle with a squeeze bulb attached. Left alone, it floated, buoyed by an air pocket within.

When you squeezed the bulb, the thing mysteriously settled to the bottom. Squeezing the bulb compressed the volume of air contained within so it could no longer float.

I seem to recall it was a small boat, maybe a submarine.

Fishing Rhino · September 30, 2010

It really doesnt affect the bass directly as much as many think.. But it does affect the food chain. Small zoo plankton are affected. If the pressure is lowering the small zoo plankton become more buoyant and thus easier for small minnows and such to feed on them. Small minnows and such then become more available and then hence the bass. When the pressure is rising and or high the zoo plankton are more stuck int he weeds and on the bottom.

I do agree with what the forage is doing, I just don't think barometric pressure has that much influence on hydrostatic pressure. And that correlation is backwards, anyway. The higher the pressure, then the aquatic creatures would have to move up to compensate. I think it has to do more with light levels, wind and current. A low pressure front moves in, clouds block the sun, there's wind, creating current, and the critters come out, followed by the baitfish, followed by the game fish.

It affects hydrostatic pressure in direct relationship to its rising and falling. When I was a kid, there was a popular toy in a bottle with a squeeze bulb attached. Left alone, it floated, buoyed by an air pocket within.

When you squeezed the bulb, the thing mysteriously settled to the bottom. Squeezing the bulb compressed the volume of air contained within so it could no longer float.

I seem to recall it was a small boat, maybe a submarine.

Fishing Rhino · September 30, 2010

It really doesnt affect the bass directly as much as many think.. But it does affect the food chain. Small zoo plankton are affected. If the pressure is lowering the small zoo plankton become more buoyant and thus easier for small minnows and such to feed on them. Small minnows and such then become more available and then hence the bass. When the pressure is rising and or high the zoo plankton are more stuck int he weeds and on the bottom.

I do agree with what the forage is doing, I just don't think barometric pressure has that much influence on hydrostatic pressure. And that correlation is backwards, anyway. The higher the pressure, then the aquatic creatures would have to move up to compensate. I think it has to do more with light levels, wind and current. A low pressure front moves in, clouds block the sun, there's wind, creating current, and the critters come out, followed by the baitfish, followed by the game fish.

It affects hydrostatic pressure in direct relationship to its rising and falling. When I was a kid, there was a popular toy in a bottle with a squeeze bulb attached. Left alone, it floated, buoyed by an air pocket within.

When you squeezed the bulb, the thing mysteriously settled to the bottom. Squeezing the bulb compressed the volume of air contained within so it could no longer float.

I seem to recall it was a small boat, maybe a submarine.

WRB · October 1, 2010

1000 millibars or 1 bar = 16.5 feet of water, 2 bars = 33'.

1 atmosphere at sea level = 14.7 psi (air pressure)

100 millibars = 1.65 feet of water

33 millibar of pressure would be very close to 6" of water, the distance the bass would need to move up in the water column to off set the added pressure on it's air bladder to maintain absolute neutral buoyancy at peak high pressure.

It's been the consensus that bass move deeper during high pressure or tighter into dense cover, which is contrary to increased barometric pressure.

Interesting facts about how water displaces pressure on a sphere of air under water is equal on all surfaces.

If you submerge a balloon filled with air it will get smaller as it descends and return to it's original size when it raises.

The bass air bladder therefor reduces in size equally as it descends in the water column and expands as it raises.

If a shallow water bass has adjusted it's air bladder for neutral buoyancy to suspend at 3 foot depth; the bass can easily maintain comfortable upright swimming down to about 18 feet, about a 15 foot depth range. Or reverse that and a bass in 18 feet can easily raise to 3 depth and be very comfortable. If you double that to 30 foot depth change, than the air bladder doubles in size, another 15 feet and it will protrude out of the basses throat.

What does this have to do with normal barometric changes on bass behavior...nothing. Normal barometric pressure has little or no affect on the basses air bladder and that was my point.

The fact is; barometric changes give us a great excuse for not catching bass or good reason to go fishing, depending on how you look at it.

WRB

WRB · October 1, 2010