Barometric pressure

[SteveG]

I've read some articles, arguing for and against the belief that barometric pressure swings affect fish activity, either directly or because aquatic insects are affected (either increased or decreased insect activity).

One of the articles stated that the pressure drop right as a front is moving in tends to increase activity. But as the storm/rain sets in and pressure starts to increase, fish hunker down.

On Penns Sunday evening, as a front was moving in, fishing was decent with lots of bug activity and risers. We then got some light rain. Monday morning was just on the cusp of heavier rain, and the water was up a bit, so I decided to work a large streamer in preparation of the rising water. It was the correct choice as I landed a nice 18" fish, and had some chases on different large streamers. But, within 2-3 hours and constant pattern/color changes, no more chases.

This is something I only recently began thinking about (the period of time in which the pressure is rising or falling). I only gave the above as an example that seems to correlate some of the information I read. What is everyone else's opinion/experience, in regard to trout or smallmouth, during pressure changes?

 

[Acristickid]

Well, high pressure equals clear skies and that means copious sunshine which most of the time I find the fishing not very good.
Although, late in the day that usually means no to little wind and that’s good for spinnerfalls.

I think grey rainy days are best. Your not as visible , the bugs stay on the water longer. All I got on that. So much science.

 

[Dave_W]

I've thought about this too.

As you point out, there is something of a conventional wisdom about barometric pressure changes wrought by approaching frontal systems, and fish activity. I think this connection is something that WW anglers who fish lakes are more attuned to than FFers focusing on trout streams. I know some bass/musky guys who will drop anything to fish before an approaching front or storm.

In my experience, there is truth to the theory, although it is more pronounced on big WW rivers. I've experienced some amazing SMB action as storms approached - we're talking (nearly) fish every cast type action. The bass were just really aggressive. It was hard to get off the water when this is happening as thunder and lightning approach. However, like everything else in fishing, it's not a sure thing. Sometimes nothing happens as the front approaches. Nevertheless, I'm usually confident as a storm or frontal system approaches, especially in the summer and autumn months.

It's also been my experience that, the smaller the stream, the less likely that this makes much difference. Trout also seem less likely to react to frontal systems and falling barometers, but I've had some good streamer days like you describe when bad weather is approaching. I'm sure we'll all agree that dreary and rainy days are often the best days to target stream trout.

Good topic!

 

[JasonC]

I’ve read that the reasoning behind this theory is that a fish’s stomach actually has more room to expand in low pressure atmosphere thus making them hungry and leading to more bites. Again, no scientific evidence behind that either.

 

[pcray1231]

So, uh, the pressure difference between high and low pressure, to a fish underwater, is absolutely miniscule. They are covered by water, which is much heavier. The difference between high and low pressure above is probably something like a fish being 24 inches deep and 24.00001 inches deep.

I have severe doubts that pressure has a DIRECT effect on the fish themselves. The pressure changes they go through in the act of rising to the surface to eat a fly far, far outweigh the pressure differences due to weather from the air above.

Direct effect on the bugs? Eh, maybe, once they reach the surface. It's theoretically easier to fly in a HIGH pressure environment. More air. But the difference is going to be pretty small, though not as small as it was on the underwater world. But my best guess is while flies tend to stay on the water longer in low pressure, it's in very small degree, if any, due to a direct effect of pressure, but more due to weather (an indirect effect of pressure).

Indirect effects on trout and bugs? Oh yeah, definitely. Pressure affects the weather.

Low pressure breeds rising air which breeds clouds. Which also tends to keep things cooler and with more relative humidity, if not outright rain. Fish feed better in clouds, and bugs stay on the water longer in high humidity (or rainy) environments, compounding the effect. Low pressure is good for trout fishing, in general.

There are exceptions, of course. Some hatches are triggered by peak temperature being reached and then beginning to fall in the evening. On a cloudy, rainy day, peak temps may be far different than what they are normally. So might put off a hatch. Wind and rain will ruin a spinner fall, as was mentioned. A cold rain can drop stream temperatures and shut off bugs and fish. A lot of rain, obviously, can bring water up or discolor it, putting off fish (or turning them on).

But the point is, weather absolutely affects fishing! And weather is an affect of pressure.

 

[afishinado]

I recently listened to a podcast with Tom Rosenbauer featuring Dr. Russ Carpenter, a fish neurobiologist from Stanford.

He discusses the effect of pressure fronts as well as the moon among other things such as fish hearing sound and their vision.

This is the most fascinating and informative thing I have heard in the long time.

His interview starts at the 40:00 min mark which I recommend listening to until the end. The discussion of weather pressure fronts and moon influence starts at the 1:17 min mark.

In short his conclusions are the change in pressure has an effect on the trout's swim bladder and causes the fish to become dormant until the pressure equalizes.

His conclusions are that during the dawn and dusk period, the current speed slows because the setting sun and rising moon influences cancel each other out at those times. and insects drift (behavioral drift) and the trout feed as opposed to this feeding being attributed to the lower light levels.

Take some time and give it a listen. You won't be sorry you did.

Orvis Podcast

 

[FarmerDave]

Pat, No argument from me on that.

Now please explain why for years, my left knee was as good as any meteorologist at predicting thunderstorms.

I have since lost this ability for the most part (because I ache all over), but when I was your age, I was a [d]walking[/d] limping barometer.

 

[Swattie87]

I think pcray's pressure affecting the weather argument is probably closer to the truth than the pressure affecting things by itself.

Weather and other downstream factors...like water flow and clarity changes that come as a result of the weather play a bigger role IMO.

Case in point...Think small freestoners in the Summer. During typical (not 2018 and so far 2019) Summers they are very low and crystal clear the vast majority of the time from about mid June to September or early October. Fishing is generally tough and slow in these conditions. The best fishing on these kinds of streams is the day immediately following a strong cold front during the Summer, not the day of the front itself, or the day before:

The day a Summer cold front rolls through PA, you have the typical hazy/hot/humid high 80's/low 90's type conditions for most of the day usually. Assume it hasn't rained in at least a few days and the streams are low and clear. Cold front comes through in the late afternoon/early evening with a line of T-storms that drop roughly an inch of rain, in a very short period of time. Streams come up and get off color, albeit for a very short period of time. The influx of water (and food) into the stream activates the feed instinct on the fish. This quick conditions change seems to have a stronger impact on Browns than Brookies IMO, but it will improve fishing for both. Again, only for a short period of time, as the water runs off fast in the Summer, and often 24 hours after the front you can barely tell it rained in terms of the flow and clarity. The pressure in this scenario would generally be falling the day of the front, and bottoming out at about the time the front passes. Pressure would then be rising throughout the day following (the good fishing day).

The day following these kinds of strong cold fronts are the nicest days of the Summer in PA...mid 70's, bluebird sunny, low humidity...The antithesis of what we generally see as "good" Trout fishing conditions. The humidity and heat usually begin to build back in pretty quickly. You only get a handful of these days each Summer, but I typically budget a couple PTO days each year to take off on short notice to fish on them.

Edit: The weather pattern in Summer 2018, and so far 2019 was largely absent of these strong cold fronts from the west. (I think I remember one in August 2018, and taking a day off to fish it.) We've been stuck in a pattern of stalled warm fronts from the south and the jet carrying precipitation along it right over us repeatedly.

 

[wildtrout2]

Swattie87 wrote:
Weather and other downstream factors...like water flow and clarity changes that come as a result of the weather play a bigger role IMO.

I agree, but you didn't mention stream temp. I believe water temp is the biggest player when it come to trout fishing "success". Big temp fluctuations put them down every time. jmo

 

[sarce]

I've had some crazy good days within about 12 hours of a major storm system arriving, especially in winter. In the summer, things can turn on like a light switch just before a storm hits. If it's a sunny day and suddenly the tops of the storm clouds roll in, it's usually game on. Storms feed on strong updrafts which are basically localized areas of lower pressure. Think of a line of storms as a wave in the atmosphere and as the edge of that wave reaches your fishing spot, fish can feel it and they will pounce on anything that hits the water. I think part of this is they don't know how muddy the water is about to turn after the storm and are trying to eat while it's still easy for them.

Obviously, don't put yourself in harms way for a fish, but in the times I've been caught out with no choice but to weather the storm...it's been outstanding fishing. Then after the storm, that first flush of runoff is also usually pretty epic, until it turns to pure mud.

 

[Swattie87]

wildtrout2 wrote:

Swattie87 wrote:
Weather and other downstream factors...like water flow and clarity changes that come as a result of the weather play a bigger role IMO.

I agree, but you didn't mention stream temp. I believe water temp is the biggest player when it come to trout fishing "success". Big temp fluctuations put them down every time. jmo

Agree, definitely. In the above Summer cold front scenario, the water temp drop is actually probably a good thing though. The cool, cloudless, low humidity evening after the front goes through may take a stream temp from the mid or high 60's during the hot weather the day before down to the high 50's, which is perfect IMO.

A temp drop from the ideal high 50's range down to the low 50's is different though...Will slow things down for sure. You get these kind of temp drops a lot with fronts in October. Good, near ideal water temps on those nice 70ish degree days, but things drop off quick when you get a cold snap.

 

[pcray1231]

His conclusions are that during the dawn and dusk period, the current speed slows because the setting sun and rising moon influences cancel each other out.

Moonrise/set has nothing to do with sunrise/sunset. i.e. the moon is as likely to rise at dawn as it is at dark, or any other time of day. Like today, moonrise is 10:40 p.m. For that claim to be true the sun and moon have to be on opposite sides of the earth from one another.

There is some tidal effect, I'm sure, though. Consult tide charts for nearest beach to determine when current speeds would speed or slow. And, keep in mind, the difference between faster current and slower current at "high" tide would depend on the direction of flow of the stream. And if it's north/south running, it wouldn't affect current, just depth on one side vs. the other.

Also, again, pressure represents the weight of the atmosphere pushing down. Under water, it's the atmosphere PLUS the water above, and water is very heavy. So a fish changes the pressure it feels by going up or down in the water, just like if you go to the bottom of a diving well, you can feel the pressure.

And, I did the calculation. The pressure difference between the lowest atmospheric pressure on earth ever recorded, and the highest, is equivalent to 4 ft of depth in water.

In more "normal" numbers, a fish that's 2 feet deep rising to the surface experiences an equivalent pressure change as a land animal going from bright and sunny to the eye of a moderate hurricane in a second or two.

i.e. atmospheric pressure is far more likely to have a direct affect on land animals, or farmer dave's knee, than it is aquatic ones.

 

[FarmerDave]

pcray1231 wrote:
So, uh, the pressure difference between high and low pressure, to a fish underwater, is absolutely miniscule. They are covered by water, which is much heavier. The difference between high and low pressure above is probably something like a fish being 24 inches deep and 24.00001 inches deep.

I have severe doubts that pressure has a DIRECT effect on the fish themselves. The pressure changes they go through in the act of rising to the surface to eat a fly far, far outweigh the pressure differences due to weather from the air above. ...

OK, I said I wasn't going to argue, but I changed my mind. A good argument is a good way to learn.

The pressure difference between high and low pressure to a HUMAN underwater would be miniscule. But would it be to a fish? Fish are way more sensitive to pressure changes. I'm not convinced.

I believe changes in atmospheric pressure do have a direct affect on fish. It may be learned behavior that dropping pressure means rain coming means more food and better cover, whatever.

Fire away Pat, I won't get upset if you intilectually kick my butt.

 

[pcray1231]

Haha,

Pressure is pressure. It's actually more than I thought. But the difference in pressure between a typical high and low pressure (we're not talking hurricanes here) is equivalent to somewhere about a foot of water.

If a fish is 1 ft deep, and pressure suddenly changes from low to high, to the fish it's like it became 2 ft deep. Can it sense that? Yeah, perhaps. Is it enough to throw the fish off any? I really doubt it. They go up and down in the water column all the time, a lot faster than pressure changes due to weather. If a fish has to equilibrate due to pressure change, then they'd have to do the same if they went from deep to shallow or vice versa.

i.e. in their environment pressure changes happen more or less constantly because they move up and down in the water column.

Humans feel pressure differences. There's a difference at sea level vs. Mount Everest for instance. But a fish goes from sea level to mount Everest in 2 ft of water depth change. One would think they are more able to handle significant pressure changes than us humans. No?

Maybe not, I dunno. But that trout sitting at 4 ft deep that shoots up for my fly, grabs it, and turns back down went from sea level to the lower reaches of space and back again in 3 seconds, in terms of pressure variation it felt. Those ones sitting on the bottom that come up near the surface for the spinner fall? Yeah, like climbing 2 everests for the evening feed. They gonna notice that today, it's more like 2 1/4 everests?

But no, a fish isn't going to tell whether the pressure came from water or air. The air is pressing down on the water. It's the same either way. Pressure is pressure.

 

[tctrout]

Agreed, this was a great interview by Tom! Highly recommended, and really made me think about trout and their behavior when related to weather...

TC

afishinado wrote:
I recently listened to a podcast with Tom Rosenbauer featuring Dr. Russ Carpenter, a fish neurobiologist from Stanford.

He discusses the effect of pressure fronts as well as the moon among other things such as fish hearing sound and their vision.

This is the most fascinating and informative thing I have heard in the long time.

His interview starts at the 40:00 min mark which I recommend listening to until the end. The discussion of weather pressure fronts and moon influence starts at the 1:17 min mark.

In short his conclusions are the change in pressure has an effect on the trout's swim bladder and causes the fish to become dormant until the pressure equalizes.

His conclusions are that during the dawn and dusk period, the current speed slows because the setting sun and rising moon influences cancel each other out at those times. and insects drift (behavioral drift) and the trout feed as opposed to this feeding being attributed to the lower light levels.

Take some time and give it a listen. You won't be sorry you did.

Orvis Podcast

 

[FarmerDave]

Pat, I'd like to discuss more, but have a Dr appointment (routine stuff). Then I might be offline until Monday.

I can't argue that the pressure change isn't miniscule. It is, but we both know that fish are a whole lot more sensitive to pressure. The laterline is like an array of pressure sensors that can detect an injured fish which is miniscule compared to changes in atmospheric pressure.

Fish in my pond would feel me walking towards the pond and swim towards me to the surface to look for pellets long before they could see me. How miniscule is that compared to changes in barometric pressure. Granted, it occurs faster, and no fat jokes please.;-)

OK, lets agree that its equivalent to a depth change of about a foot.

You don't think fish can recognize where they are at?

You don't think a fish can tell whether or not they moved?

I am not convinced that the fish can't detect barometric pressure change and as a result, react to it out of instinct, just like my catfish react to anyone walking within 20 feet of the pond.

 

[PennypackFlyer]

I'll say that it looks like the pressure from Pat will keep FarmerDave off the Fly Fishing Forum for several days.

 

[pcray1231]

I can't argue that the pressure change isn't miniscule. It is, but we both know that fish are a whole lot more sensitive to pressure.

It's not that I think it's miniscule. It isn't really. A foot of water is a lot of pressure!

And yes, I think they can detect it. Heck, I can detect it! You feel pressure when you go under water. When you go deeper, you feel it get more pressure. Right? Yeah, I think fish can detect pressure, I'm not arguing that point.

The part I can't fathom is that this level of pressure variation has any real effect on them. The pressure changes on them a lot. They go up, down in the water column. Get up under a rapid, then out to the slow pool. I challenge that a small, slow change, as would be due to atmospheric pressure changes, affects their behavior when much larger, faster pressure changes are part of their everyday lives.

i.e. if their swim bladders get messed up as high pressure moves in. Well, go somewhere a foot shallower. It's all equal again!

I observe fish moving into shallower areas or deeper areas depending on time of day and other factors. The pressure effects of this movement are considerably larger than that from the atmosphere. Many move out of a deep pool into a shallow riff to feed. That'd be like very sudden super low pressure to them, no? Why do their swim bladders not get messed up from that?

As for a guy walking next to a pond. Yes, I think they sense vibration and sound (which is a pressure wave, hehe). An unnatural vibration spooks them, because it's associated with predators.

Indirect effects of pressure? Sure. Light, water temp, flow rates, etc. Even O2 levels. Hasn't been mentioned that higher pressure means more dissolved oxygen stays in solution. Maybe the higher oxygen of high pressure, increases metabolism, but the sunlight keeps them spooked. Then in evening of a high pressure day, they are really really hungry. But on a low pressure day, with less oxygen in the water, their metabolism is less. Combine that with clouds and an all day opportunity to lazily feed, and they won't be as aggressive at chasing things or feeding quite as heavy this evening.

 

[poopdeck]

I can only add for SMB since trout are of little interest to me. Basically I only care if the water is at fishable levels. I don't concern myself with pressure, moon phases, temperatures, sun, clouds, tides (unless I'm fishing tidal water), sun spots or anything else. I would say the only thing that matters is ones ability to get out and actually present something the way it should be presented. Everything else is minutia. I would drive myself mad if I had more factors to concern myself with. I guess I didn't help at all.

 

[FarmerDave]

PennypackFlyer wrote:
I'll say that it looks like the pressure from Pat will keep FarmerDave off the Fly Fishing Forum for several days.

No idea what this means. There is no pressure on me from anyone on this site. I enjoy these discussions with Pat, because he is one of the smartest people I know. Ever notice how our discussions are much shorter? ;-)

Was hoping to take a vacation day to work around the farm, but it's raining [d]again[/d] still. So I decided to save the vacation day. Will definitely be off grid after today.