Pressure change. What's a lot? What's

[Chris at Tech]

So in all the reference I've read on pressure changes on fishing, I still have a few basic questions.

What's reading is considered 'low pressure'?  Is there a mb range, or is that term just used to indicate a drop of pressure?  How about 'high pressure'?  Is there a range or is it just used to indicate a rise from previous readings?

What's a 'big' change in pressure?  2mb?  3mb?

And building on that, what's a rapid change in pressure?  How many mb over how much time?

Obviously, there's not a set range, but I'd like to get a better idea of how to interpret pressure readings I see from the weather services.

Thanks

Chris

[Raul]

Never mind the pressure, look at the weather associated with it. A drop in 3, 4, 5 mb on a sunny clear cloudless day has no effect and so is the opposite.

[Guest ouachitabassangler]

I don't consider atmospheric pressure to be "weather" in the sense the word includes all characteristics of the atmosphere as relating to bass behavior. For instance, air temperature changes don't affect water temperature directly like overnight, so has no effect on bass if the temp drops from 80 to 55 overnight, then warms back up the next day. Eventually a general cooling of the air will of course cool the water and change their behavior, but that takes days when all sorts of weather (series of fronts) can roll in and out. Or a stationary high can result in no wind and general heating of a region, pressure remaining stable, but air temp rising, affecting anglers but not fish. I consider air pressure a product and a measure of weather, a result of passage of a mass of colder, heavier air replacing warmer, lighter air (cold front), or the reverse, a measure of how dense the air is.  Pressure can change dramatically without changing what most of us refer to as weather, such as high winds, storms, rain, snow, heavy clouds, bluebird skies. While it doesn't necessarily make a different type of weather that affects us, pressure does directly affect bass behavior, and a move of one millibar up from 29 to 30 within a few hours can cause bass to go a few feet deeper belly on the bottom or bury up deeper in thick cover. On the other hand a drop from 30 to 29.7 can stimulate bass feeding activity. Small pressure changes taking place over a whole day have a delayed effect on bass, while sudden change has a profound effect. My ears pop sometimes when pressure changes quickly, and the bite changes about as quick as the pop happens.

Carry a barometer fishing and check that out.

Jim

[Raul]

If a drop in air temperature doesn 't affect the water temperature neither does a drop in the atmospheric pressure, water is 800+ times denser than air.

[RoLo]

Barometric pressure is significant only insofar as it's associated with a change in "air temperature".

If a change in barometric pressure is not accompanied by a change in air temperature, it's a "non-event".

A depth change of just a few inches will change the pressure on a fish, more than any change

in barometric pressure.

           I have caught countless fish in the ocean from water over a hundred feet deep.

By the time the fish reaches topside (air pressure: 15 lb / sq in) their eyes are bulging out of their heads

and their stomachs are literally heaved into their throats. Now 'that' is a change in pressure,

and no, there is no catch-and-release in deep-sea fishing.

Roger

[.ghoti.]

As an indicator of temperature changes, cloud cover changes and rain, barometric pressure can can be considered significant.

Barometric pressure itself, has little effect on the fish. Hee's the numbers, from an old instrument tch, for those interested.

The record high was 32"Hg, recorded in Siberia, don't remember the year. The record low was 25.7"Hg recorded in a south China sea typhoon. Again, I don't remember the year. In this country, extreme bp's are considered to be from 28.5 - 30.5"Hg That's a deltaP of two inches of mercury, which is a little less than one PSI, and a little more two feet of water column.

For more exact numbers use the following.

1"Hg = 33.864mBar

1PSI = 2.02"Hg

1PSI = 27.7"W.C.

A typical front, as it moves through the area, may cause a drop of 8mBar.

8mBar = 0.236239"Hg = 0.11695PSI = 3.24"W.C.

That means, the fish has to moved down 3.24 inches to maintain the same pressure on it's body, after the front passes.  I'm not a biologist, I'm a techno-geek, I don't know what this means to the fish. As just pressure, it can't mean much, but as an indicator of inclement weather, and the prospect of easy meals washing into the water, it has to be significant.

Just my $0.02

[senile1]

I'm not a barometric pressure expert, but everything I've read indicates that barometric pressure affects the air bladder on a bass.  And from what I've read regarding these effects, this is an inexact science but there are some general conclusions that can be made.  These conclusions seem to agree with what Jim stated in the quote below.  I, myself, have noticed that a sharp rise in pressure does seem to shut the bite down while a drop can turn the bite on.  Of course, this is only my own anecdotal evidence.  Maybe some of you have experienced something different.  

I don't consider atmospheric pressure to be "weather" in the sense the word includes all characteristics of the atmosphere as relating to bass behavior. For instance, air temperature changes don't affect water temperature directly like overnight, so has no effect on bass if the temp drops from 80 to 55 overnight, then warms back up the next day. Eventually a general cooling of the air will of course cool the water and change their behavior, but that takes days when all sorts of weather (series of fronts) can roll in and out. Or a stationary high can result in no wind and general heating of a region, pressure remaining stable, but air temp rising, affecting anglers but not fish. I consider air pressure a product and a measure of weather, a result of passage of a mass of colder, heavier air replacing warmer, lighter air (cold front), or the reverse, a measure of how dense the air is. Pressure can change dramatically without changing what most of us refer to as weather, such as high winds, storms, rain, snow, heavy clouds, bluebird skies. While it doesn't necessarily make a different type of weather that affects us, pressure does directly affect bass behavior, and a move of one millibar up from 29 to 30 within a few hours can cause bass to go a few feet deeper belly on the bottom or bury up deeper in thick cover. On the other hand a drop from 30 to 29.7 can stimulate bass feeding activity. Small pressure changes taking place over a whole day have a delayed effect on bass, while sudden change has a profound effect. My ears pop sometimes when pressure changes quickly, and the bite changes about as quick as the pop happens.

Carry a barometer fishing and check that out.

Jim

[RoLo]

I'm not a barometric pressure expert, but everything I've read indicates that barometric pressure affects the air bladder on a bass.

Every part of the fish's anatomy (for that matter the human anatomy) is affected by barometric pressure.

However, our bodies are designed to easily tolerate these natural changes in atmospheric pressure

and for the most part we're unaware of their existence.

Fish on the other hand are cold-blooded animals. Consequently, anything that affects

water temperature will affect the disposition, movement and metabolism of bass.

It's an involuntary process in which the fish has no say (their behavior is dictated by water temperature).

Bottom Line: Air temperature affects water temperature, but barometric pressure does not.

I, myself, have noticed that a sharp rise in pressure does seem to shut the bite down while a drop can turn the bite on.

A rise in barometric pressure is typically accompanied by a drop in air temperature.

A drop in barometric pressure is typically accompanied by a rise in air temperature.

It has always been my belief that a rise in barometric pressure that is not accompanied

by a drop in air temperature is a 'non-event'. That is to say, barometric pressure is a symptom

rather than a cause.

Bass in shallow water are the first fish affected by air temperature changes,

but a persistent change in air temperature eventually affects bass in deep water as well.

Roger

[Raul]

Rolo, how come you say what I was going to say before I say it ? just wonderin '.

[RoLo]

I'm glad to hear that

Roger

[senile1]

RoLo,

You have said a couple of times that barometric pressure doesn't affect water temparature.  (I've included your last quote below.)  I agree with that statement.  And it is your contention that the pressure has nothing to do with the bass's behavior.  It is only the water temperature that is affecting the bass.  What I have read is that barometric pressure affects a bass irregardless of any correlation in the air temperature.  I have seen very high barometric pressures with warm, clear, sunny days and these can be some of the more difficult days to put alot of fish in the livewell, at least in my experience.  I've also had storms come in where the pressure drops dramatically but the temperature doesn't, and I've caught alot of fish.  The water temperature in these instances remained fairly constant.  This link describes the supposed effect that barometric pressure has on the swim bladder of a bass, irregardless of the temperature.  (http://home.comcast.net/~rkrz/infoarch/fyibarometer.htm)  I'm just trying to learn here by playing the devil's advocate.    Are there any fishery biologists out there who have definitive evidence regarding this?

I'm not a barometric pressure expert, but everything I've read indicates that barometric pressure affects the air bladder on a bass.

Every part of the fish's anatomy (for that matter the human anatomy) is affected by barometric pressure.

However, our bodies are designed to easily tolerate these natural changes in atmospheric pressure

and for the most part we're unaware of their existence.

Fish on the other hand are cold-blooded animals. Consequently, anything that affects

water temperature will affect the disposition, movement and metabolism of bass.

It's an involuntary process in which the fish has no say (their behavior is dictated by water temperature).

Bottom Line: Air temperature affects water temperature, but barometric pressure does not.

I, myself, have noticed that a sharp rise in pressure does seem to shut the bite down while a drop can turn the bite on.

A rise in barometric pressure is typically accompanied by a drop in air temperature.

A drop in barometric pressure is typically accompanied by a rise in air temperature.

It has always been my belief that a rise in barometric pressure that is not accompanied

by a drop in air temperature is a 'non-event'. That is to say, barometric pressure is a symptom

rather than a cause.

Bass in shallow water are the first fish affected by air temperature changes,

but a persistent change in air temperature eventually affects bass in deep water as well.

Roger

[RoLo]

What I have read is that barometric pressure affects a bass irregardless of any correlation in the air temperature.

Yes, I have read that theory as well, many times.

I have seen very high barometric pressures with warm, clear, sunny days and these can be some of the more difficult days to put alot of fish in the livewell, at least in my experience.

That's a tough one.

I've had 'bad' fishing days in all sorts of weather, and I've had 'great' fishing days in all sorts of weather.

I can't say unequivocally that I remember a great day that I can attribute 'solely' to a falling barometer.

I will say this, frontal conditions without a temperature change are normally accompanied by Wind

and Overcast Skies". Both of these factors cause a change in "Underwater Visibility", a whole other ballgame.

Predatory fish have rod-and-cone vision while forage fish do not. The eyesight of gamefish

adjusts far more rapidly to changes in lighting conditions than that of baitfish.

Exploiting their advantage, gamefish instinctively become active during transitional periods of lighting

caused by overcast skies, windblown water surface and time-of-day.

This is the underlying magic of Dusk, the so-called "Magic Hour".

There is no biologist who can provide us with a definitive answer to the questions

of barometric pressure, solar effects, lunar affects, et al, I'm afraid we're left to our own devices.

Roger

[senile1]

Your points are well-taken, RoLo.  A basses behavior can be affected by a number of things and some educated guessing is involved in determining a pattern.  I think most of us are going to be on the water, trying to find what the fish want, no matter the conditions anyway.  (Except maybe during a lightning storm.)

[Raul]

Are there any fishery biologists out there who have definitive evidence regarding this?

Weeeeeeeelllllllllll, I 'm not exactly a fisheries biologist, I 'm a veterinarian that has worked in Mexico 's fisheries department and who wrote his graduate college thesis on bass, so you can say that I know a thing or two in anatomy, physiology, behavior n ' stuff like that about bass. Fish have always fascinated me and I 've been a fish hobbyst since I was five.

[Guest ouachitabassangler]

I'll agree air pressure changes on the surface don't directly afect water temperature. So what do we KNOW about air pressure? Air pressure most definitely affects boiling of water, as well as it's freeze point. Pressure is higher at the bottom of a column of water than at the top of it, and the 16 pounds of air weight on a square inch of your head is a lot less 3 miles up because there is less air pressing down. Add the weight of a column of air to a column of water and you get increassed water pressure.

Air pressure very directly affects water properties, and affects fish. High pressure can indicate cooler or warmer air temperatures. This summer the southeast will probably suffer the regular set-in highs that result in increased temperatures and little or no wind. Those conditions sometimes last a month or more for miserable weather with no clouds for shade.

It's likely the air bladder is expanded during a drop in pressure on the water (low air pressure), due to lowered air pressure inside it, so bass rise to deflate the bladder to normalize pressure of the bladder against internal organs. The bladder holds them upright, but a too-full bladder would float them up higher than they want to be. It's easier for them to expel air than to gain air because air gets into the bladder through the blood stream more slowly than it departs, and it takes more time for the bass to extract enough oxygen from water to add air. When pressure on the water (high air pressure) increases water pressure from all sides against a bass, the bladder must shrink, compressing air, the blood stream both absorbing oxygen at first, then adding it back later to allow the bass to suspend higher. A shrinking air bladder would send the bass deeper to compensate, to be where water pressure matches bladder pressure. As the bass gets hungry below the baitfish which are not as affected, the blood stream begins pumping air back in so the bass can be comfortable suspending higher. Keep in mind the air bladder mostly allows the bass to remain upright without having to use fins and tail to do that. The air bladder is a finely tuned organ that when changed directly affects the mood of a bass.

http://www.kokodafishing.com/static/newsletter/newsletter_v060326.html

http://www.humminbird.com/generic.asp?ID=404

Here's another interesting article at http://www.quickoneplus.com/fish/barometric.htm

Jim

[Raul]

Here we go........again :, you guys talkin bout swimbladders have the slightest idea on how the swimbladder works, from where the gas inside it comes and to where it goes ? you are just speculating on what the swimbladder does.

The swimbladder's main function is that of a hydrostatic organ.  Neutral buoyancy, the ability of an organism to use little or no energy to stay at particular levels of water, is achieved through the expanding and shrinking of the swimbladder due to varying gas pressures.

When a fish dives, it 's swimbladder is compressed as a result of the increase in pressure at greater water depths.  So in order for the fish to return to its former, higher level in the water, the swimbladder must be reinflated.  Therefore, the most essential function of the swimbladder is the regulation of gases coming in and out of the fish's body.  Thus it is necessary for fishes to be efficient controllers of their buoyancy.

DEFLATION:

On the posterior wall of a closed swimbladder lies a network of capillary beds.  Next to these capillaries is a muscular valve, the oval, which has the job of controlling gases exiting the swimbladder.  Within the oval there are two types of muscles-- circular and radial.  When the circular muscles are relaxed, the radial muscles are contracted in order to stretch the swimbladder out, which in turn creates a greater capillary surface area for diffusion.  Gases from within the bladder diffuse out to the blood through these capillaries.  When sufficient levels of gases have been removed to create a new level of buoyancy, the circular muscles contract.  Now the oval is no longer in contact with the bladder and so the gases are not able to diffuse from one area to another.  A fish "knows" its buoyancy through the responses of nerve endings to the stretching and shrinking of the bladder wall.  So with any change of pressure within the swimbladder as a result of diving or surfacing, a message can be relayed to the brain to initiate the deflation or inflation of the swimbladder so that the fish can maintain neutral buoyancy. The movement of gases from the bladder through the oval is a slow process however, taking over several hours to adjust to just a small pressure change.

INFLATION

The swimbladder has an interesting way of retaining gases.  The inner lining of the swimbladder consists of numerous gland cells collectively called the gas gland.  When the gas volume within the swimbladder is low this gland reacts by releasing lactic acid into the blood, acidifying it.  With acidification, the blood releases oxygen where it accumulates in the rete mirabile.The rete mirabile ("wonderful net") is a bundle of close-lying arterial and venous capillaries that diffuse gases between one another as blood is carried through them, in and out of the gas gland.  The rete mirabile, much like the oval, requires a large surface area for optimal contact between the arterial and venous capillaries.The diffusion of oxygen out through the bladder wall is blocked by a thin layer of crystalline guanine, thus also maintaining the volume of the swimbladder.

In order to restore gases to a deflated, closed swimbladder, the rete mirabile and the gas glands must create a combined pressure greater than that pressure within the swimbladder.  Oxygen, having been forced off hemoglobin by lactic acid, is retained in the venous capillaries of the rete.  Because of the rete's parallel arrangement of venous and arterial capillaries, a countercurrent multiplier effect occur.  This is when gases are able to diffuse from a higher oxygen volume in the venous to the lower oxygen volume in the arterial capillaries, therefore keeping more oxygenated blood within the loop of the rete. When the pressure in the rete exceeds that of the swimbladder, oxygen diffuses out of the rete and into the bladder.  The idea of multiplication comes into effect when we look at the varying lengths of capillaries that make up the rete.  The longer the capillaries are, there is a greater surface area for gas exchange.  So, with longer capillaries, a greater oxygen pressure can be created.This can be most important to those fish who spend the majority of their time at great depths.  With an increase in swimbladder pressure as a result of the greater water depth, the fish would have a harder time keeping gases from being lost from the system.  Therefore, those fish found in deep waters, where the pressure is greatest, generally have longer capillaries that make up their rete so that there is a greater surface area for gas exchange.

[RoLo]

Thanks for giving me a breather Raul

It gets tired after a while, going over the same stuff, over & over & over.

Understanding the purpose and function of the swim bladder (not all fish have them)

handily rules out the theory that largemouth bass shuttle back-and-forth between deep & shallow water.

Not surprisingly, telemetry studies have resounded the expected result. The bigmouth bass

is a homebody that stubbornly resists rapid depth change. Otherwise the largemouth would not possess

a swim bladder, which are reserved for fish that maintain a relatively constant depth.

A swim bladder makes rapid depth change more difficult, for instance, try swimming downward

in the water while holding a beach ball in your arms, or try swimming upward while holding

a bowling ball. Just as they say, fact is stranger than fiction

Roger

[senile1]

I would guess that most everyone on this forum has an area of expertise that they could teach to others.  (Mine is network engineering.)  You guys who know the most about  the Bass's swim bladder should not be surprised that you have to answer many questions about it.  The only way the rest of us can learn what you know is by debating, and asking questions.  As new people come to the forum, some of these questions will be asked over and over.  That's one of the reasons why the forum and this site is so great.  

Having said this, I've learned more about this subject from this thread than from all of my reading in the past.   Thanks, Raul and RoLo.  Just don't let it go to your heads.  

[ernel]

I am far to lazy to retype one of my earlier post concerning pressure changes. This is only an opinion, but it makes since to me.

There are a few things that will help to understand what is actually happening if you keep a few things in mind. First thing is that the barometer is changing constantly. Small increnmental changes are happening every minute of every day, even when the barometer is so called steady. It is not the small changes that are having a positive or negative effect on the fish, it is the major changes. There are two types of frontal systems that can effect your next fishing trip.

A cold front is by far the most dreaded by a fisherman. Not because of the approaching frontal system, but due to the effect after a cold front has passed. Most cold fronts are accompanied a drastic drop in the barometric pressure as the front approaches. Then a short lived low steady pressure. Then a fast drastic rise in pressure. Sometimes even higher than before the front moved through your area. As the low gives way to high pressure, the winds change direction and funnel cooler or even down right cold air from the N-NE. The high will also bring higher winds. The stronger the high pressure system on the back side of the low/cold front, the higher the wind speeds will be. This occurs more in the late fall through the early spring. A cold front does not always produce percipitation, but if there is enough moisture in the air, it will.

This is only my opinin here, but I feel the greatest effect on the fishing is actually caused at a much smaller level. By this I mean on the zooplankton. Zooplankton are effected becuase they have less tolerance to the drastic change in the temperature that comes with the frontal passage. The bait fish that eat the zooplankton, are effected by not haveing as much of a buffet to choose from for a few days. The baitfish are also effected by the increased light penetraton. These two thing will cause them to become less liklely to be out and about moveing around. First because there diets have become restricted, and because they are now even more visible when in open water.

I said all of that to say this. Fishing can be some of the best of your life just before and as a cold front passes into your area. But it can be the hardest after a cold front passes. Not only because of the increase in the B/P, but due to the increased sunlight. Sunlight does not hurt a basses eyes. If it did, then they would have eye lids so they could close them. It does however it make it harder for them to conceal themselves from their inteded prey. Bass will hide in cover just as much for security as they also do to conserve energy. If catching their prey is hard to do, then they are not going to be actively chasing shad that can see them coming from a greater distance. This would be a waste of energy. Bass have learned over time that their chances for finding food will increase in a few days and they just need to conserve for a few days. So with the after effect of the frontal system still effecting their physical aspect, and the addition of increased light l/m bass are going to be moving to one of two places.

Some bass are going to be pulling back out to deeper water. Some are going to be buried in or even leaning on cover. Grass mats, submerged hydrilla, brush piles, and non-floatin or floating boat docks with vertical posts are good places to start. Floating docks without the post don't seem to be as productive for me. The ones seeking cover are of course the ones that remained shallow, and are going to be more spooked. Flipping and pitching jigs and texas rigged worms tight to cover can be, and normally are the most productive for me. Key word here is tight. The thicker and nastier the cover looks the better chance that it will hold a bass. The more isolated the cover is, the more chances that it will hold multiple bass as well. A quiet approach is a must in this situation. Not only in the lures entry into the water, but in the amount of noise that is made in the boat. Sometimes it is the repeated action of casting to the same spot over and over again, and others it is the continued presence of a shaking lure that is staying too long in the bass' home that will draw the strike. Mostly I start out looking for a reaction bite first and for most. A heavy lure that will punch through a grass mat works wonders for drawing reaction strikes. It just quietly appears from above and the bass has the choice to run from it or remove it from it's home. Most bass are not gong to run from a something invading it's home.

Now for the ones that have moved out to deeper water. This will vary how far and deep they move as to what type of lake your are fishing. A genereal rule of thumb, is they will pull back to the first break line from where they were before the front passes. A break line can be as small as a 2 foot change on some lakes and as much as 50 or more on others. It could nothing more than the creek channel that is winding through a flat. For the ones that have made the drastic move to deeper water, I will more than likely be using the dreaded vertical approach of the drop-shot. Sometimes this is the only thing that will draw a strike. Other times it may be the even more dreaded jigging spoon. If the depth change is not as drastic, as in just sliding futher down a sharp point, then I will use a carolina rigged finnesse worm as well. I am just looking for something that will stay in their faces as long as possible without alot of movement. The fish are not wanting to move much, so they are not going to want a bait that is acting all kinds of active and crazy. The bait should act as if it was effected by the frontal passing also.

Now for the second type of frontal system. A warm front. These is one that can be more detremental to you than the fish. It is mostly associated with the coming of spring and summer. It can bring the onslaught of severe thunderstorms and other severe weather as winter fully looses it's grip and gives way to the coming summer.

Sorry for the long post, but there is alot of thenings that an be said for frontal passages and the effect on fishing. I however will leave it at this.

Like I said I am way too lazy to type all that again.

[Guest ouachitabassangler]

Since there's interest in the technical stuff we might as well put everyone on the whole of it.

http://www.bio.davidson.edu/Courses/anphys/2000/Martin/introduction.html

Jim

[gatrboy53]

i think all of you are getting way in over your head on this. im no expert but i did stay at a holiday inn last nite!!!!! ;D ;D ;D