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Does high/low air pressure really affect fish behavior? If it does is it a physical thing or learned behavior since low pressure systems are often associated with cloudy days and high pressure with sunny days?
I have always heard that a high pressure system puts the fish down and makes them harder to catch. It seems to be especially common theme amongst bass fisherman. Earlier this year I was smallmouth fishing on a river with a guide and he brought up the subject saying that high pressure “made the fish feel uncomfortable” since the pressure was pushing down on the water and, therefore, the fish. He also thought it affected their air bladder.
I made the comment that it didn’t seem logical that higher air pressure cold make a fish feel uncomfortable since water, or any liquid, can’t be compressed – so how would it know what the pressure was above the water. That’s why the hydraulics on my tractor works so well, right? I realize that deeper water has greater pressure due to the increased weight of the water but would higher air pressure do the same thing?
So, I guess my real question is can fish really “feel” higher or lower air pressure?
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Yes, barometric changes definitely changes fish behavior - BUT - after a lifetime of fishing and hearing both sides of the argument, I believe it to be the RATE of change, rather than the DIRECTION of change.
N.E. Texas 2 acre and 1/4 acre ponds
Original george #173 (22 June 2002)
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Rob,
A fish's lateral line is believed to be exquisitely sensitive to pressure changes. Although water is not compressible, pressure changes still register.
I don't doubt that atmospheric pressure changes fish behavior. However, atmospheric changes are trivial in comparison to simply swimming from say 4' to 5' depth. I think the behavior change is not about comfort, but more about survival instincts related to feeding or reproduction.
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low pressure systems are often associated with cloudy days and high pressure with sunny days I think is has more to do with sunnny and cloudy days and maybe windy v. calm conditions. Bobad is right, the pressure changes that occur simply due to changes in water depth are much greater than the swings you see in everyday barometric pressure and are likely trivial.
Last edited by Shorty; 10/12/07 09:15 AM.
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low pressure systems are often associated with cloudy days and high pressure with sunny days I think is has more to do with sunnny and cloudy days and maybe windy v. calm conditions. Bobad is right, the pressure changes that occur simply due to changes in water depth are much greater than the swings you see in everyday barometric pressure and are likely trivial. Shorty, what causes the fish to go up or down?... 
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Original george #173 (22 June 2002)
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Shorty, what causes the fish to go up or down?... I'm sure it has something to do with swimming around and finning.
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Shorty, what causes the fish to go up or down?... I'm sure it has something to do with swimming around and finning. Isobars on a weather map indicate barometric pressure gradients, indicating both wind direction and velocity - weather changes – clear to cloudy – warm to colder – precipitation (clear/turbid water) - etc. All documenting changes in barometric pressure that makes the fish go up or down...
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Original george #173 (22 June 2002)
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http://www.ngpc.state.ne.us/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=010762Daryl Bauer, one of the posters on this archived thread, is one of Dr. Willis former students and one of our State biologists. I am not sold on barometric changes being the "sole" reason fish behavior changes as there is a whole host of other changes going on at the same time during swings in the barometer. Keep in mind that the pressure changes at different depths are much greater than those that typically occurr in the atmosphere. So is it soley the barometer, or the other changes that are going on as well? I can tell you that I have had some fantastic days of fishing when the conventional wisdom regarding the just barometer changes says I shouldn't have.
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low pressure systems are often associated with cloudy days and high pressure with sunny days I think is has more to do with sunnny and cloudy days and maybe windy v. calm conditions. Bobad is right, the pressure changes that occur simply due to changes in water depth are much greater than the swings you see in everyday barometric pressure and are likely trivial. Shorty, what causes the fish to go up or down?... Increased light penetration with sunny days associated with high pressure?
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
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Don't have time to find it now but did you guys know that low pressue in Hurricanes has been known to cause fish kills?
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
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http://www.fishingclub.com/document.asp?dID=3774 Hundreds of thousands of fish died after rain from Hurricane Isabel washed low-oxygen water and organic matter out of swamps and into rivers across northeastern North Carolina last month.
Low pressure? or something else?
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I think it makes sense as someone has mentioned above that a rapid change in barometric pressure would affect fish behaviour. Consider that as the barometer falls rapidly a fish will have to let air rapidly out of it's air bladder to maintain neutral bouyancy and keep himself from floating to the surface. The opposite would occur when pressures repidly increase. Of course fish do this all the time when they change depth but I imagine that a fishes overall internal systems might be somewhat upset by having to adjust it's bouyancy compensation even when they are not changing depth. Of course slow changes will be less noticeable. I think this is likely to explain changes in behaviour. It's just like when you go up in an airplane and your ears become uncomfortable until things equalize. Or have you ever been sitting in your car in a parking lot when the car next to you begins to move and you feel like it's you that is moving? All these kinds of things are somewhat unsettling to living beings because they are abnormal or mentally confusing. That's my theory, unproven but makes sense to me. I believe that if a fish didn't have an air bladder he would not be affected by atmospheric pressure. It would also make sense that a hurricane could kill fish if you consider that atmospheric pressure could drop so fast that their bladders explode. A fish can only change their air bladder so fast. What happens if you catch deep water fish and bring them up rapidly. If you are scuba diver you know what an embolism is.
Gotta get back to fishin!
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http://www.fishingclub.com/document.asp?dID=3774 Hundreds of thousands of fish died after rain from Hurricane Isabel washed low-oxygen water and organic matter out of swamps and into rivers across northeastern North Carolina last month.
Low pressure? or something else? Shorty, What you mentions does happen of course but I've actually read of extreme low pressure that drops rapidly causing fish kills out at sea during a hurricane. I believe it was mentioned in one of the SRAC ract sheets in regards to nitrogen bubble sysdrome (the bends). I'll see if I can find it.
Last edited by Cecil Baird1; 10/12/07 01:01 PM.
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
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I think it makes sense as someone has mentioned above that a rapid change in barometric pressure would affect fish behaviour. Consider that as the barometer falls rapidly a fish will have to let air rapidly out of it's air bladder to maintain neutral bouyancy and keep himself from floating to the surface. The opposite would occur when pressures repidly increase. Of course fish do this all the time when they change depth but I imagine that a fishes overall internal systems might be somewhat upset by having to adjust it's bouyancy compensation even when they are not changing depth. Of course slow changes will be less noticeable. I think this is likely to explain changes in behaviour. It's just like when you go up in an airplane and your ears become uncomfortable until things equalize. Or have you ever been sitting in your car in a parking lot when the car next to you begins to move and you feel like it's you that is moving? All these kinds of things are somewhat unsettling to living beings because they are abnormal or mentally confusing. That's my theory, unproven but makes sense to me. I believe that if a fish didn't have an air bladder he would not be affected by atmospheric pressure. It would also make sense that a hurricane could kill fish if you consider that atmospheric pressure could drop so fast that their bladders explode. A fish can only change their air bladder so fast. What happens if you catch deep water fish and bring them up rapidly. If you are scuba diver you know what an embolism is. Also keep in mind some fish have an air duct that connects their air bladder to their esophogus to blow out excess gas that builds up from rapid pressure changes while many do not. Trout salmon and catfish have this opening but bluegills, bass, crappie etc. do not. Fish that have this opening are called phyostomas.
Last edited by Cecil Baird1; 10/12/07 01:00 PM.
If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.
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Bobad wrote: However, atmospheric changes are trivial in comparison to simply swimming from say 4' to 5' depth. Atmospheric pressure is double at a water depth of 34ft compared to what it is at the surface. There is more of a pressure change going from a depth of 4ft to 7ft than you would see from the pressure change of an approaching hurricane. Fish go through these pressure changes in depth all the time with little or no consequence. Now when you bring fish up from real deep water, some can have real problems with the extreme change in pressure changes being exerted by the water depth. At a depth of 100ft the pressure is 3 times what it is on the surface. At sea level the air pressure is 14.7 psi. Anyone else ever take scuba diving lessons?
Last edited by Shorty; 10/12/07 01:27 PM.
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Dang it, Shorty, you beat me to the math. And did it correctly, to the best of my knowledge.
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I hope I did it correctly Theo, it's been twenty plus years since I had scuba lessons.  http://www.challengers101.com/Pressure.html Scuba divers know that as you go down to greater depths, the water pressure increases. In fact, the increase in pressure is 14.7 psi for every 34 feet of additional depth. A diver that descends to a depth of 100 feet must withstand a pressure of ...
( 100 ft / 34 ) x 14.7 = 43.24 psi
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Atmospheric pressure is double at a water depth of 33ft compared to what it is at the surface. There is more of a pressure change going from a depth of 4ft to 7ft than you would see from the pressure change of an approaching hurricane.
Anyone else ever take suba diving lessons?
I did once about 15 years ago. I was taking a lesson in a swimming pool while on vacation in St Lucia. I panicked. Not sure why, I'm not claustrophobic - at least I didn't think I was. Anyway, I had a great instructor and 2 days later he had me 50 feet below the surface. Great experience. Back to your example that atmospheric pressure is double at 33 feet than at the surface. Don't you mean the pressure exerted on a human in 33 feet of water is double that of the air pressure at the surface? What I was trying to get at with my question is, since liquids don't compress how could a change in air pressure above change the water pressure below. I don't doubt that fish react to high/low pressure but I was looking more for a scientific/physics explanation. Besides, that guide I was on the river with was very cocky about the whole subject. I'd love to prove him wrong. 
Last edited by RobA; 10/12/07 01:33 PM.
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Back to your example that atmospheric pressure is double at 34 feet than at the surface. Don't you mean the pressure exerted on a human in 34 feet of water is double that of the air pressure at the surface?
Yes in terms of the psi exerted, 14.7 psi at the surface, 29.4 psi at a depth of 34 ft, with an increase of 14.7 psi every 33-34 ft you go down.
Last edited by Shorty; 10/12/07 02:28 PM.
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Interesting subject - same discussion on a different forum... http://www.danblanton.com/viewmessage.php?id=91847
N.E. Texas 2 acre and 1/4 acre ponds
Original george #173 (22 June 2002)
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I read that George an it was very enlightning. I wonder how the UV index also changes before and after a front comes through and what affect that might have as well.
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will this knowledge help any of us catch fish? expound on that.
for me, i kind of look at it like tony perez used to say about the "science" of making contact with a baseball......"see the ball, hit the ball"
we have all these fancy electronics these days, and the knowledge of how fish relate to structure......so locate the fish, and give em yer best presentation.
GSF are people too!  
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will this knowledge help any of us catch fish? expound on that. Help catch fish? I just wanted to shut the fishing guide up.
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If you cant catch fish, you have stinky fingers.
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If you cant catch fish, you have stinky fingers. It seems to me that if you CAN catch fish, you have stinky fingers. Is this a classic catch 22?
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