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Rising water temps

IMO.....Often its the combined factors which come into play with the low pressure that make conditions favourable, ie; Westerly winds, Rain, And Warmer temps, (especially in Winter). When these all act favourably the fish "Will" feed, it`s getting the timing right with them that counts.
In the Summer too, pressure differences come with these changes which can make them feed or not.
And a rule I was told as a kid and remembered easily because it rhymes, "When the wind blows from the East the fish bite least, and, When the wind blows from the West the fish bite best"!!
 
I appreciate that many of us have become restless with this post. When I used to watch Young Scientist of The Year, I picked up many tips.

Sam wrote: And water is compressible but had very little to do with any of this. Which confuses me as Jim stated he didn't understand the influence of air pressure on water pressure, then went on to try and lecture me on hydraulic systems
Someone also said solids are incompressible...... Lectures on electron degeneracy pressures by PM only because I'm bored now....

Sam regarding your post above. I did say that to all intents and purposes, water is not compressible. I'll stick to that. My examples in connection with hydraulics were intended to demonstrate that point.

I have done a little sum on the effects of barometric pressure. I've calculated the pressure (100mb) at a depth of 1 metre, I hope that it's correct. These figures are approximate. I've carried out these calculations in millibar because that's what the weather forecasters use to describe lows and highs.

Atmospheric pressure is assumed to be 1000mb
at one metre depth water pressure is 100mb
A fish feels the combined pressure 1100mb

If atmospheric pressure drops to 950mb
Water pressure at 1 metre is constant at 100mb
A fish feels a combined pressure 1050 mb
A drop in pressure on the fish of 1050/1100 about 5%

If atmospheric pressure increases to 1050mb
Water pressure at 1 metre is constant at 100mb
The fish feels the combined pressure of 1150mb
An increase in pressure on the fish of 1150/1100 about 5%

If the fish were at 2m, the water pressure would be 200mb and the pressure change on the fish, based on a low of 950mb or high of 1050mb would result in a drop or increase of about 6%.

This shows that the bulk of the pressure difference on a fish is down to changes in atmospheric pressure rather than the depth the fish is at. This wasn't obvious to me, but quite interesting. If these sums are correct, and I'd be grateful for anyone to check them, then this may explain one or two observations of fish behaviour.
 
Sam Lloyd said:
If the atmosphere is 950mbar it will be 1150 mbar at 2 meters. If the atmospohere is 1050 is will be 1250 at 2 metres. So its a difference of 1.45 PSI :)

As for how much mater is compressed, someone has already quoted wiki as saying its 1.8 percent. I've never said it would affect shallow depths, I just conrrected a common misunderstanding ;)

Merry xmas Dave
Click to expand...

1.4%...hmmm. If you care to look again, is exactly what I said in my original post Sam (rounding down apart :D)....strange that.

Yes, water compresses by the rather minimal, almost irrelevant amount of 1.8%.....if truly silly big amounts of pressure are applied, pressures that never will be applied in normal circumstances. which in other words means that under all normal circumstances, to all practical intents and purposes, water is effectively incompressible.

I think we have done this one to death now Sam :D:p:D

Merry Christmas to you young sir, and all the other reprobates who frequent this den of iniquity, and have a happy, healthy and prosperous new year.

Don't drink too much though lads...the falling down liquid does often mean that parts of the anatomy strike very hard objects...and those body parts most certainly are compressible :D:D

Cheers, Dave.
 
Jesus H this is hard work. Air pressure has a very big impact on the dissolved oxygen levels in water. High barometric pressures equal a higher level of dissolved oxygen. Unless this gets abnormally high it makes fish, Barbel especially, work better, digestion rates increase and usually they will be on the lookout for food. It’s fairly basic stuff guys.
 
So is it high pessure or low pressure that makes the little fishes jump on my hook? I'm confused now.

Let's start again from the beginning. Sam, can you please explain the pressure thinggy again?

Thanks :D
 
Kevin Daly said:
Jesus H this is hard work. Air pressure has a very big impact on the dissolved oxygen levels in water. High barometric pressures equal a higher level of dissolved oxygen. Unless this gets abnormally high it makes fish, Barbel especially, work better, digestion rates increase and usually they will be on the lookout for food. It’s fairly basic stuff guys.
Click to expand...

Except that's the exact opposite of what my results would suggest. I.e low/falling pressure is good, high/rising pressure is bad. I've no doubt air pressure plays a big part in the fishes lives but i don't think it's as simple as you suggest. Look at the weather at the moment - low pressure, warm rain - got most of us thinking about going fishing. At this time of year high pressure usually means freezing temperatures and i'm sure most would agree that's not good for barbel fishing.
 
Some more thoughts on air pressure: https://barbel.co.uk/site/vbulletin/forum/barbel-talk/621-air-pressure.html

To add yet another twist to the debate i would also add that when taking all these conditions into consideration how you interprate them depends on what you want from your fishing. Take Pauls data in the above thread - all based on captures of big fish. I've often said that good conditions for big fish are the bad conditions generally - i.e. on the bad days when most fish aren't feeding, the big ones have to to maintain their bulk. That's not to say big fish don't feed on the good days - it's just that with every other fish on the munch your chances of getting a big one are less - Unless you adopt tactics to specifically target the big ones but let's not go there for now!
 
Andrew Boyne said:
How right you are! ;)
Click to expand...

i know;)

great link by the way just had a browse some interesting results!
i also agree with your sentiments on the big girls having more chance of slipping up without the bait tester's;)
this leads to grey areas where results aren't great for the majority but there's a few big lumps falling to the lucky few!

my opinion is there's not one deciding factor it's a culmination of:

1:location
2:moon phase (which i think effects the air pressure)
3:air temps/water temps
4:river levels
5:confidence
 
I think fish just like change. Rising river, falling river, I catch. Rising temps, falling temps, I catch. Rising barometer, falling barometer, I catch. But if things have been stable for a week or so I struggle.
 
Adrian Williams said:
I think fish just like change. Rising river, falling river, I catch. Rising temps, falling temps, I catch. Rising barometer, falling barometer, I catch. But if things have been stable for a week or so I struggle.
Click to expand...

I almost put you in that 10% there Ade then you went and ruined it with that last sentence! :D
 
David Gauntlett said:
1.4%...hmmm. If you care to look again, is exactly what I said in my original post Sam (rounding down apart :D)....strange that.

Cheers, Dave.
Click to expand...

Strange you seem to think psi stands for percent..... Just about sums up you and others arguments :rolleyes: It's actually a 8.7% difference.

PSI is pounds per square inch just for future reference Dave ;)
 
Jim Foxall said:
I appreciate that many of us have become restless with this post. When I used to watch Young Scientist of The Year, I picked up many tips.

Sam wrote: And water is compressible but had very little to do with any of this. Which confuses me as Jim stated he didn't understand the influence of air pressure on water pressure, then went on to try and lecture me on hydraulic systems
Someone also said solids are incompressible...... Lectures on electron degeneracy pressures by PM only because I'm bored now....

Sam regarding your post above. I did say that to all intents and purposes, water is not compressible. I'll stick to that. My examples in connection with hydraulics were intended to demonstrate that point.

I have done a little sum on the effects of barometric pressure. I've calculated the pressure (100mb) at a depth of 1 metre, I hope that it's correct. These figures are approximate. I've carried out these calculations in millibar because that's what the weather forecasters use to describe lows and highs.

Atmospheric pressure is assumed to be 1000mb
at one metre depth water pressure is 100mb
A fish feels the combined pressure 1100mb

If atmospheric pressure drops to 950mb
Water pressure at 1 metre is constant at 100mb
A fish feels a combined pressure 1050 mb
A drop in pressure on the fish of 1050/1100 about 5%

If atmospheric pressure increases to 1050mb
Water pressure at 1 metre is constant at 100mb
The fish feels the combined pressure of 1150mb
An increase in pressure on the fish of 1150/1100 about 5%

If the fish were at 2m, the water pressure would be 200mb and the pressure change on the fish, based on a low of 950mb or high of 1050mb would result in a drop or increase of about 6%.

This shows that the bulk of the pressure difference on a fish is down to changes in atmospheric pressure rather than the depth the fish is at. This wasn't obvious to me, but quite interesting. If these sums are correct, and I'd be grateful for anyone to check them, then this may explain one or two observations of fish behaviour.
Click to expand...

Jim, you calculations are almost right. In short what would happen now, if you recalculated for 2 metres or 3 metres, is the effect of atmospheric pressure would decrease as a percentage of the total pressure. The change in pressure would be the same at all depth though.

the formula you need to use is actually (1-total/atm)*100 for the percentage due to pressure. And to compare two days (1-total day1/total day2)*100, (total being for whatever depth you're interested in.
 
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Jim Foxall said:
Geoff, your post makes a lot of sense to me. Just a couple of points to add. Many people think that atmospheric pressure makes a difference and I've never understood this as water is not compressible. I'm not saying they're necessarily wrong, but it makes little sense to me. Secondly, I guess that if we have a lot of "warm rain" from the west and this runs straight into the rivers, as it is at the moment, it must have a bearing on the river water temperature. Wouldn't be surprised if today would be a good day to be on the bank.
Click to expand...

You clearly said you didn't understand .....
 
Sam Lloyd said:
Strange you seem to think psi stands for percent..... Just about sums up you and others arguments :rolleyes: It's actually a 8.7% difference.

PSI is pounds per square inch just for future reference Dave ;)
Click to expand...

Sam...you are getting sadder by the minute old son. It's done mate, we have had our fun, let it go. It's the season of goodwill, we're done with that...we wan't to talk about how many rods we own, have a choice of two threads to wish each other a merry Christmas, and swap silly innuendos :D Get into the spirit man...one way or another.

Cheers, Dave.
 
David Gauntlett said:
Sam...you are getting sadder by the minute old son. It's done mate, we have had our fun, let it go. It's the season of goodwill, we're done with that...we wan't to talk about how many rods we own, have a choice of two threads to wish each other a merry Christmas, and swap silly innuendos :D Get into the spirit man...one way or another.

Cheers, Dave.
Click to expand...

Given into insults now you realise you don't know what your talking about then. :) merry xmas Dave.
 
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