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Posts: 479
Location: Northern Illinois | I really believe the relationship between barometric pressure and fish activity illustrates the difference between correlation and causation. Fish activity may not be caused by changing pressure but may be correlated to it. |
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Location: Green Bay, WI | RLSea - 10/6/2017 11:15 PM
I really believe the relationship between barometric pressure and fish activity illustrates the difference between correlation and causation. Fish activity may not be caused by changing pressure but may be correlated to it.
Bingo! No more calls folks, I think we have a winner.
TB |
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Posts: 32781
Location: Rhinelander, Wisconsin | For a number of years during the 70's and 80's my friend Jim Cairnes and I kept meticulous logs of every fish caught and used barograph records from the community colleges we taught classes for. We concluded that small 'ripples' combined with solunar activity periods were correlated to fish activity, that movement up or down was usually a good thing, and that the largest fish we caught were more usually than not dissociated with any data, including wind speed and direction, barograph readings, time of day, depth, etc. We were able to identify several factors that usually included fish activity, but never were able to predict a unknown 'big fish' would move. Lots of possibilities there as to why not, and most seemed to be random events. The capture of targeted big fish had more to do with time spent fishing for that particular fish than anything environmental we could identify, but targeting that fish under the correct subset was a definite positive. |
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Location: Green Bay, WI | In regards to changing atmospheric pressure, here's the thing...
In the water column, the effect of depth on pressure is MUCH more significant than the effect of changing air pressure. For every foot change in water depth, the pressure changes by about 0.43 psi in fresh water. Therefore if you change depth by about 34 feet, you've changed pressure by about one entire atmosphere. For air pressure at sea level there is about 14.7 psi of pressure, which corresponds to 29.92 inches of Mercury. So let's say now that the barometer increases to 30.92 in Hg, for the sake of argument. That's a change of about 0.49 psi, give or take.
(1/29.92) * 14.7 = 0.491
So the point is that for a significant change in barometric pressure (1 in Hg), a fish only has to move a little over 1 foot in depth to experience the same relative change in pressure. And that's assuming the fish is near the surface where any such change in barometric pressure would be more likely to be perceived by said fish. If the fish was 10-15 feet down for instance, the amount of hydrostatic pressure they perceive due to their depth may well overwhelm any such change in barometric pressure.
I realize that it's a hydraulics problem, but it's not a simple one. Air pressure applied to the surface of the water (a fluid) is equally distributed throughout the fluid in all directions. However it's not a perfect hydraulic system in that there are irregularities in the "tank" per se--e.g.; contours of depth interfere with pressure wave transmission; variations in bottom hardness result in more/less compliance of the tank, and therefore may not reflect pressure changes uniformly back into the water column; currents (and wind I suppose) apply opposing pressure waves to alter pressure changes imposed by barometric pressure from the atmosphere. It would seem that these things can all confound even distribution of pressure changes in an open system such as a lake.
Thus I can only conclude that the direct effect of atmospheric pressure changes on fish in a water column are likely very minimal, compared to the hydrostatic pressure changes those fish experience simply by moving up or down a small distance in the water column. Therefore it seems very likely that the environmental changes that accompany said barometric pressure changes (changing light, changing temperature, changing visibility due to wave action, etc) are more responsible for any increased or decreased activity levels in fishes. At least that's what my logic is telling me anyway...
TB |
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Posts: 8715
| I think the mystery behind post frontal high barometer fishing is little more than the fact that they all just ate yesterday ahead of and during the front. |
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Posts: 32781
Location: Rhinelander, Wisconsin | tcbetka - 10/7/2017 10:41 AM
In regards to changing atmospheric pressure, here's the thing...
In the water column, the effect of depth on pressure is MUCH more significant than the effect of changing air pressure. For every foot change in water depth, the pressure changes by about 0.43 psi in fresh water. Therefore if you change depth by about 34 feet, you've changed pressure by about one entire atmosphere. For air pressure at sea level there is about 14.7 psi of pressure, which corresponds to 29.92 inches of Mercury. So let's say now that the barometer increases to 30.92 in Hg, for the sake of argument. That's a change of about 0.49 psi, give or take.
(1/29.92) * 14.7 = 0.491
So the point is that for a significant change in barometric pressure (1 in Hg), a fish only has to move a little over 1 foot in depth to experience the same relative change in pressure. And that's assuming the fish is near the surface where any such change in barometric pressure would be more likely to be perceived by said fish. If the fish was 10-15 feet down for instance, the amount of hydrostatic pressure they perceive due to their depth may well overwhelm any such change in barometric pressure.
I realize that it's a hydraulics problem, but it's not a simple one. Air pressure applied to the surface of the water (a fluid) is equally distributed throughout the fluid in all directions. However it's not a perfect hydraulic system in that there are irregularities in the "tank" per se--e.g.; contours of depth interfere with pressure wave transmission; variations in bottom hardness result in more/less compliance of the tank, and therefore may not reflect pressure changes uniformly back into the water column; currents (and wind I suppose) apply opposing pressure waves to alter pressure changes imposed by barometric pressure from the atmosphere. It would seem that these things can all confound even distribution of pressure changes in an open system such as a lake.
Thus I can only conclude that the direct effect of atmospheric pressure changes on fish in a water column are likely very minimal, compared to the hydrostatic pressure changes those fish experience simply by moving up or down a small distance in the water column. Therefore it seems very likely that the environmental changes that accompany said barometric pressure changes (changing light, changing temperature, changing visibility due to wave action, etc) are more responsible for any increased or decreased activity levels in fishes. At least that's what my logic is telling me anyway...
TB
TB,
We compared hundreds of fish catch spikes during minimal but measurable barometer readings during both relatively stable and trending up/down conditions. The most interesting to me were the spikes during stable weather where mid day activity on sunny/cloudy days, regardless of wind direction or sunlight, correlated to minor but measurable changes up or down. The small changes usually lasted a half hour or so and would move back up or down to the mean line over a couple hours, and catch spikes were more prevalent during solunar events, using the Kinght Solunar book (There was no internet at the time) . The changes one would see above the water were minor wind shifts, for example going from S SE to SE then back the S SE again. Frequently surface activity would pick up, as did bird and shore critter activity.
We were never able to ascertain why fish react to those changes, but they do, even when lakes have 30" of ice.
Example: A high/cold/clear, Wisco NW winds post frontal, 6 tip ups, no action for two hours, wind shifts slightly to N (barometer rises a bit), action occurs, wind shifts back to NW (barometer drops back), action continues until wind shift is back to NW, then shuts down.
One comment, post cold frontal conditions seemed to have more effect on WHERE (one water body to another, and even on a single lake or river) the fish would be active, not IF, windows would be much shorter.
I've noticed the little changes really can have a short effect on the crappie bite, especially when they are suspended. Not a clue why.
Note: The barograph used paper charting. Old school all the way. |
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Location: Green Bay, WI | All interesting stuff--and I certainly can't explain the observations you made while ice fishing. In fact, one could argue that of all the anecdotal stuff being reported, ice fishing would seem to be LEAST susceptible to changes in barometric pressure. Curiosity here, but did you (or have you ever) notice that ice makes cracking noises more frequently when the barometer changes rapidly? I can't imagine that it would have an effect, but I've never paid attention to that aspect.
I think it basically boils down to this: It will be virtually impossible to prove a correlation between changing barometric pressure and fish activity, because it's virtually impossible to isolate the changing barometric pressure. It always seems to be accompanied by some other weather-based or environmental phenomenon. In medicine we used to call this sort of thing a "constellation of symptoms" (or signs), in that it usually wasn't just one thing that pointed to a diagnosis...but rather a grouping of (seemingly) related findings that helped you to figure it out.
TB
Edited by tcbetka 10/7/2017 1:40 PM
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Posts: 32781
Location: Rhinelander, Wisconsin | Ice cracking is mostly a rapid cooling issue. The little rises and drops I was referring to were quite small, and not accompanied by any visible changes in cloud cover or anything discernible than a slight temporary shift in wind direction. One of the barographs was very close to where Jimmy was fishing, and one was here in Rhinelander. |
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Posts: 1828
| Interesting note on barometer: This Saturday we had it down to 29.28 in Hg, which is the lowest (by far) I've ever fished through. really strange because it wasn't a storm or anything - just a little windy. In the fall it seems like the observable weather with respect to barometer is anomalous for some reason.
Fish were going pretty good through the day with the pressure tanking, but not crazy. |
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Location: Green Bay, WI | jaultman - 10/9/2017 7:32 AM
Interesting note on barometer: This Saturday we had it down to 29.28 in Hg, which is the lowest (by far) I've ever fished through. really strange because it wasn't a storm or anything - just a little windy. In the fall it seems like the observable weather with respect to barometer is anomalous for some reason.
Fish were going pretty good through the day with the pressure tanking, but not crazy.
What was the cloud cover where you were fishing, and (if you recall) what was the water temperature?
TB |
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Posts: 1828
| foggy in the morning, fog burned off mid-morning and it was sunny the rest of the day. We fished dawn til dusk with action spread out all day. Water temp started just over 48 and ended just over 52. cold night, small shallow lake.
barometer 29.5 at dawn, bottomed out at 29.28 mid afternoon, started rising. Typically those readings would coincide with a storm, but it was far from stormy. In any case, I continue to love falling and and bottomed out barometer.
Edited by jaultman 10/9/2017 9:19 AM
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Location: Green Bay, WI | jaultman - 10/9/2017 9:14 AM
foggy in the morning, fog burned off mid-morning and it was sunny the rest of the day. We fished dawn til dusk with action spread out all day. Water temp started just over 48 and ended just over 52. cold night, small shallow lake.
barometer 29.5 at dawn, bottomed out at 29.28 mid afternoon, started rising. Typically those readings would coincide with a storm, but it was far from stormy. In any case, I continue to love falling and and bottomed out barometer.
Great information, thanks for the report! This is an interesting topic for conversation--and one that warrants further study...even if it's just anecdotal reporting.
TB |
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Posts: 497
Location: Ludington, MI | Unbelievably low water temps. We've been stalled at 65 or higher for two weeks. |
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Posts: 4269
Location: Ashland WI | tundrawalker00 - 10/9/2017 1:39 PM
Unbelievably low water temps. We've been stalled at 65 or higher for two weeks.
Yes. Where were you fishing Jaultman? |
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Posts: 1828
| small shallow lake, northern MN |
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Posts: 32781
Location: Rhinelander, Wisconsin | The Whitetails were all over the place this weekend after the storm passed through, out in the fields and moving several times from dawn to dusk on a rising barometer Sunday. My grandson Kaden shot a doe (dropped her with a perfect shot from his 7mm-08) during the youth hunt yesterday afternoon, pretty cool.
Saturday the rain was unreal up here so I worked in the office. I worked on getting ready for the Spring Bay Fall outing yesterday, should have been fishing.
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Posts: 90
| jtmenard - 10/2/2017 1:37 PM
My highest is 30.25 which was Saturday when it was falling.
It's a small sample size (98 fish), but this is what I've found...
29.60-29.69....3.1%
29.70-29.79....8.2%
29.80-29.89....23.5%
29.90-29.99....25.5%
30.00-30.09....33.7%
>30.10...........6.1%
Are you switching tactics during different pressure readings? I understand if you don't wish to answer. |
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