Generally speaking, low pressure is better fishing than high pressure, e.g., the dreaded cold front moving in turns things off. However, drastic/rapid changes in pressure in either direction can shut things down, too.



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I have to wonder how atmospheric pressure can alter anything at all under the water as it it so much denser. Anyone care to elaborate on this?

 

Pz=Po + 0.0967*z

Pz is pressure in water depth
Po is pressure at surface
z is depth in meters

Though I don't think pressure is the reason for the fish feeding activity/inactivity. Oxygen levels increase in water when a low pressure moves in. The fish feed more actively because of premium oxygen levels. I could find more on this but it would take some searching, been away from this for a couple yrs so I am rusty on formulas.

 

I follow biometric pressure more then the Solunar tables. I find I catch more fish when the pressure is falling( just before the storm).

This link may help
http://www.anglerwise.com/2010/02/09/how-does-barometric-pressure-affect-fishing/

 

But it doesn't say why?

 

It's a rapid change in pressure, usually from high, stable pressure to low that really messes up fishing. But like others have said, the small time frame right before and the start of a storm can be stellar.

 

It's a rapid change in pressure, usually from high, stable pressure to low that really messes up fishing.

Anyone have any idea why this is the case?

 

Look it up and let US know argh. I personally don't care cuz everyday is a good day for fishing.

 

External Weather Factors

In Denny Richard's book Fly-Fishing Stillwaters for Trophy Trout, chapter 13 "External Factors" he touches on the effects of barometric pressures.


"Approaching storm fronts are synonymous with falling barometric pressures, and over the past decade I've tried to monitor trout behavior during these periods. Invariably, trout become almost dysfunctional. As the barometer falls, so does the level of activity. Fish tend to be sluggish, completely non-aggressive, have little if any interest in feeding, and, if given an opportunity, will slink off to deep water and hold up until the weather improves.

Most often, these periods of inactivity will coincide with a barometric pressure reading of under 30.

Fishermen can use a barometer to predict the level of fish activity as effectively as a television weatherman uses it to predict weather changes.

When the barometric pressure reading hits 29.7 or lower, I find that trout become sluggish and rarely respond to food. The lower the barometer falls, the more dramatic the impact. My advice is to stay home and tie flies. A twist, however, is while the barometer is skidding just before a summer thunderstorm, trout activity can approach frenzy levels. I've had some of my finest moments fishing as a storm front hovers on the horizon. But once the front hits and the barometer stabilizes on the low-side, fishing is usually poor until the barometer moves above 30.0. I rarely concern myself with barometric pressure readings during periods of extended fair weather. When the barometer reading stabilizes around 30.2, trout feed fairly consistently. I rarely see the barometer get above 30.5, so it's a guess as to how trout behave when that happens."

Quick water temperature swings, four days during the full moon phase and a north wind. Are a few other external weather factors that may have a negative impact on trout activity and angler success Denny also touches on.

GG

 

It has been known for a long time that the barometric pressure has an effect on fishing. How the pressure directly effects the fish is still not fully understood, but knowing how to use the barometric pressure readings can greatly increase your chances of catching fish, especially in shallow and fresh waters.

Barometric pressure is the measure of the weight of the atmosphere above us. It exerts pressure on the waters we fish and even on us. In fact, it can change how well some people feel. It is believed by many, that it may have a similar and even more dramatic effect on fish effecting their feeding habits.

Measurement of barometric pressure is accomplished with the use of a barometer. A barometer measures the weight of the atmosphere per square inch (pressure) and compares it to the weight of a column of mercury.

The first instrument was invented in 1643 by Evangelista Torricelli. His barometer used a glass tube from which all air has been removed (a vacuum) and is inserted into a container of mercury that is exposed to the pressure of the air. The air pressing down on the mercury in the container forces an amount of the mercury up into the glass tube. The height to which the mercury rises is directly proportional to the pressure of the atmosphere. This is usually measured in inches (inHg) or in millibars (1 inHg equals 33.864 millibars).

Today aneroid barometers, invented by the French scientist Lucien Vidie in 1843, are the most widely used instrument to detect air pressure. An aneroid is a flexible metal bellow that has been sealed after removing some of it's air (a partial vacuum). A higher atmospheric pressures will squeeze the metal bellow while a lower pressure will allow it to expand. This expansion of the metal is usually mechanically coupled to a dial needle which will point to a scale indicating the barometric pressure.

A new form of barometer uses a pressure transducer. This transducer is like a miniature aneroid barometer that converts the amount of air pressure into a proportional electrical voltage. This voltage then can be fed into a digital readout and/or into a computer.

Barometric pressure varies with altitude. A higher elevation will have less atmosphere above it which exerts less pressure. To keep readings standard across the world, barometric pressure is to be indicated at sea level. Therefore, readings at elevations other than at sea level will require a correction factor which is based on the elevation and the air temperature (colder air weighs more and will require a greater correction).

The barometric pressure changes as the weather systems over us changes. When you look at a weather map that has those blue "H"s and red "L"s, this is indicating the areas with High and Low pressure. It is worth noting that the areas with high pressure are the areas with good weather, and the areas with low pressure are the areas with bad weather. Barometric pressure has been used by weathermen since the beginning of meteorology to predict the weather. It can also be used by fishermen to predict the quality of fishing, and more importantly, how to fish.

As a general guideline, think of 30 inHg (1016 millibar) as being a normal level. World records vary from a high pressure of 32.0 inHg in Siberia to 25.7 inHg during a typhoon (both readings are off the scale of most barometers). For the US, extreme levels can be considered as 30.5 inHg and 28.5 inHg. When it comes to fishing, a change of just +/- 0.02 inHg from normal is enough to effect their feeding habits.

It is important, however, to note that the effects of barometric pressure is greater in fresh and shallow waters, than it is in deeper waters. This is probably due to the fact that the pressure of water is so much greater in deeper waters making the air pressure above it no longer having any significance.

Some general rules regarding barometric pressure are:

Pressure Trend

Typical Weather

Fishing Trends

Suggested Tactics

High

Clear skies

Fish slow down, find cover or go to deeper waters.

Slow down lures and use baits more attractive to fish. Fish in cover and in deeper waters.

Rising

Clearing or improving

Fish tend to become slightly more active

Fish with brighter lures and near cover. Also fish at intermediate and deeper depths.

Normal and stable

Fair

Normal fishing

Experiment with your favorite baits and lures.

Falling

Degrading

Most active fishing

Speed up lures. Surface and shallow running lures may work well.

Slightly lower

Usually cloudy

Many fish will head away from cover and seek shallower waters. Some fish will become more aggressive.

Use shallow running lures at a moderate speed.

Low

Rainy and stormy

Fish will tend to become less active the longer this period remains.

As the action subsides, try fishing at deeper depths.


It is important to note that after a long feeding period, the action will slow regardless of the following conditions. On the flip side, a long period of poor fishing conditions may be followed by a really good one.

It is also important to note, that the barometric pressure is just one of many factors that effect fish feeding habits. Other effects include water temperature, light, tidal forces, water clarity, the pH level, water levels, wind/surface disturbance, boat traffic, fishing pressure, and so on. Another good judging factor of fishing is the solunar effects which play a role in the tidal and illumination factors.


As noted above nobody really seems to know just why this affects feeding habits.

 

I found this as it shows a direct link with oxygen fixing with hemoglobin and atmospheric pressure as a straight-line graph.

http://www.anesthesia2000.com/physics/Chemistry_Physics/physics21.htm

....just some more info.

 

So, with the knowledge that atmospheric pressure is transferred through the water column and pressure affects the ability for oxygen to bind to hemoglobin ( low pressure allows less oxygen to bind to hemoglobin binding sites) then, atmospheric pressure must affect fish activity. With respect to fish feeding-frenzy just before a storm, this must be due to an anamoly in the atmospheric pressure. This could also coincide with an increase in the oxygen level of the water when it cools down thus absorbing more oxygen after a fasting by the fish, just some thought here!

 

http://midcurrent.com/science/the-pressure-myth/

 

"A rise or fall in barometric pressure, such as with an approaching cold front, usually means a shift in the weather pattern. And it is the change in the weather, not any fluctuation in barometric pressure, that affects both the fish and the fishing. In fact, most saltwater species probably aren’t even aware of barometric variations".



Fair enough, so maybe not directly affected...but it does indirectly affect them by causing changes in the weather

 

You have a handful of vacation days per year. You decide to use some to fish one of your favorite lakes. The weather is supposed to be good but there are reports that a front may move through. You:

A) Decide to stay home and hit up the local fish farm. You're not happy unless you're guaranteed fish.
B) Fish your destination. You've been planning this trip for months and you'll have a good time even if the fishing isn't the hottest.
C) Go to a different lake; the prospects are better there.
D) Stay home an mow the lawn. You forgot there's a full moon this week as well, so your vacation will need to wait a couple of weeks.

 

B and C. I did B while I was there, and another couple of guys did C (a lake in the same relative area) and faired pretty well.

 

Jack Shaw discusses barometer levels and trends in his Book Tying Flies for Trophy Trout .

My experience is trout do not like extremes at either end as others have mentioned sudden shifts. A rapid drop to bad weather and cold temperatures is the worst in my experience. But I don't necessarily think it's the weather change itself but perhaps that insects know not to hatch when the weather is really awful with heavy rain or hot and sunny. I also have observed insect will emerge on windy days more heavily when the wind abates - if only a bit.

Trout like all salmonids are photo-phobic; adverse to light and seek deeper water in bright light. Reaction also depends on species and stock. True kamloops trout are far more likely to 'sulk' than domesticated stocks that will continue to readily feed when kamloops fish have gone off the bite.