Barometric Conditions

[motalot]

Does anyone out there study the barometer in relation to how the fish are biting. What are your views on this ?

It has always been my experience with freshwater fish at least, the they don't bite during a dropping pressure, or generally low pressure.
One thought I had after observing some trout in an extremely deep hole, was that perhaps they go deeper, or move to deeper water, to make up for some of that drop?

Another thing, if it is about to rain, they will generally go off the bite, but then once the rain starts to fall, they will start biting.

Fish bite better in rising or higher pressure.The reason behind this is simple. All fish have airsacks in there stomaches, when the air pressure is low there air sacks expand making the fish feel full or bloated.

There is an old saying " bar at 1020 there will be fish a plenty"
When the wind blows east, the fish bite least, when the wind blows west the fish bite best!

Probably be better discussing prevailling wind conditions and strength, along with cloud cover, temperature, time of year(and its influence on insect larve on the surface), etc rather than making blanket assumptions based on barometer pressure.

One rule to go by is, concentrate on fishing shallow water during air pressure drops, deeper water during air pressure rises. Air pressure changes impact on the fishing more in the fall, winter and early to mid spring. This might be because fronts that pass during this time of year tend to come from the north and northwest, while late spring, summer and early fall frontal systems often come from the south and southwest. The colder weather fronts that come from the north and northwest involve more drastic barometric pressure changes, while the warmer weather fronts associated with coming from the south and southwest involve relatively mild pressure changes. While you forward to the day's fishing when it's as clear as the proverbial bell, not a cloud in the sky, you're not likely to encounter great fishing because the barometric pressure readings are probably very high. That reasoning is a lot more plausible than guessing that it's too bright and the bass have no eyelids, and this is the reason for them being off the "bite".

This is just a few things I have studied lately and was wondering what you guys can add.

[Bonefish]

As a general rule, deep water fish with smaller bladders are less affected by low BP conditions. Large bladder fish move deeper seeking higher pressures. During long periods of low pressure, fish compensate and adjust to the lower pressure conditions and will begin to feed again.

During high BP condition, fish seek cover from shallow structure. As the BP pressure begins to drop, the fish will move to sturcture a little deeper. When the BP is rising, fish move out of the deep water and start to feed after a day or so. When the BP begins to drop, especially after a long high BP pressure period, fish feed like crazy. As the BP continues to drop, the fish seek deeper water and do not feed. And when the BP is lowest, fish move to deep structure and do not feed.

As you know, other natural factors like moon phase, water temperature, oxygen levels, wind, boat traffic and food avalibility may enter the equation.

[motalot]

That is good information. I am trying to put all this together and as you say moon phase and all other conditions affect things as well. Wish someone would come up with a nice computer program to figure this out for me..lol

[Bonefish]

Me too. I forgot to add the affect of the season changes. Somewhere in all of this we should find a good fish day. This fall the water levels have added another factor to all of this.

[Grumpy]

I would like to add some things which I will para-phrase (rather than quote because it is too long)from SPOONPLUGGING a "GUIDE TO LUNKER CATCHES" by Buck Perry, the father of structure fishing.

BUCK SAYS:

When fishing YOU SHOULD NOT THINK OF WEATHER IN TERMS OF TEMPERATURE OR PRESSURE.—You should VIEW WEATHER IN TERMS OF LIGHT. The lighter or brighter it is, the tougher the fishing will be. The darker the conditions, the better it will be.

(Grumpy’s note: Buck is generally referring to daytime and SUMMER TIME conditions here.)

Using the COLD FRONT as our starting point, lets look at it in terms of LIGHT. The pre-frontal conditions are normally dark conditions, with heavy cloud cover (and a falling barometer), rain or showers. After the front goes through, the cooler mass of air moves in (with rising barometer) and you will normally have a bright clear, blue sky.

PRE-FRONTAL CONDITIONS, WILL GIVE GOOD FISH MOVEMENTS (feeding) AND POST-FRONTAL CONDITIONS WILL GIVE BAD, OR LITTLE MOVEMENT OF FISH (not feeding).

The day following a cold front normally has a clear blue, washed out sky. A beautiful day, and usually windy.. FISH—DEEP AND INACTIVE...

(Grumpy’s note: Buck goes on to list conditions for the next few days after a cold front passes, each day getting clouder and less bright, with increasingly better fishing condtions.)

The day of a cold front—heavy threatening clouds, threatening rain and falling pressure. When the rain starts, the fish will have already moved into the shallow water and will be biting like crazy.

The day after the front passes will dawn BRIGHT AND CLEAR, high pressure will have set in and the fish will have gone deep.

The cycle repeats itself over and over, sometime longer and sometimes shorter, in between fronts but it never stops changing.

(Grumpy's note: I hope this helps.)

Grumpy

[Bonefish]

You know, Grumpy, I like this explanation. It makes sense to me some how. Maybe it is the simplicity which goes a long way.

[motalot]

okay now explain how moon phases come into affect with these conditions. For instance what about full moon conditions and a falling bp?

[Moose1am]

WARNING! Long Post coming up! Enter and read at your own Risk! :)

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I love these type of discussions. Remember that fish don't have eyelids that they can close to shut off light. And I don't even think that they have a pupil either. So you might say that I am in the light corner of this discussion.

So light definitely does effect the fish.

A fish's buoyancy bladder is used to keep the fish upright and to maintain buoyancy in whatever depth the fish swims.

Fish live in water and thus are affected by WATER PRESSURE. The swim bladder is effected by WATER PRESSURE.

Cold water makes the air inside a fish get colder. Cold air shrinks in size or in scientific terms make the air molecules VIBRATE LESS. Pressure is the bouncing of the air molecules against the sides of the balloon or the air bladder.

Fish have diurnal cycles. Day and night. Light Conditions changed on a 24 hour cycle with the rising and setting of the sun as the Earth spins around it's axis.

Water is much denser than air. If you were to go from the surface to 33ft down you would experience a pressure change of just 1 ATM or 760 mm Hg. If you were to go from the earth's surface to 50,000ft you would experience a change of one atmosphere as well. One atmosphere of pressure is the sum total of all the air molecules above us when we are at sea level. When you dive to 33 ft you are under 2 atm of pressure. 1 atm from all the air above the surface of the water and one atm from the 33 ft of water column above you for a total of 2 atm. A fish can change depths easily and any air pressure changes above that impact the water pressure on a fish at any depth can be corrected by the fish simply with a depth change. So IMHO the fish change depths due both to the changing light conditions and the changing water pressure. But the changes in the amount of light penetrating the water is much greater than any water pressure changes. It just take too much air pressure change to really effect the water pressure. That's due to the fact that water is so much more dense than air. Air can easily be compressed into a much smaller volume. You just can't do that with water. In fact in Science and in Chemistry we take great precautions when working with air samples. Scientist have to report air sampling values along with the corresponding air temp and pressures. When working with water samples that's not necessary. Air samples taken at 10 deg C would give different results or concentrations if they were taken at 25 deg C. In fact temperature effects the results much more than air pressure. Only if you were to take samples in the high mountains would you have to really take into consideration the difference in the air pressure in the reported results. Pv=nRt

Fish do react to changing conditions. Chances in the angle of the sun to the water's surface is definitely one of those factors. If you fish a lot you know that getting on the water before the sun comes up is important when catching fish especially in the summer months when the sun gets very high in the sky in June or July. Also fishing changes as the sun sets. And night fishing is getting more and more popular. Crappie fishermen put out LIGHTS to fish at night.

I personally think that the entire changing weather conditions effects the fish. I often wonder what the fish would do if they could leave the water during a thunderstorm when there is lighting all around the lake. I know we fishermen head home for cover when there is lightning or we hear a coming thunderstorm. Fish can't leave the water and I think that fish go deeper to avoid the shock from any lightning striking the water. Maybe that is why they seek the shelter of heavy brush when there is a big storm. Or maybe they are seeking protecting from the bright sky the next day after the storm passes.

I would like to see some research notes on how fast a fish can adjust the amount of air inside their swim bladders. I know that a fish's swim bladder just like it's stomach is surrounded by many blood vessels. The blood vessels can pass air molecules in or out of the gas bladder or swim bladder. Just like our lungs can absorb air into our blood stream so can the air be absorbed by the fish's swim bladder into the fish's blood vessels. And gas can pass from the blood vessels into the swim bladder. The fish adjusts the amount of air inside the swim bladder so that it's always balancing the water pressure surrounding the fish when the fish dives or surfaces.

Have you ever seen pictures of a Great White Shark Attacking a seal at the surface of the ocean. Or have you see a large mouth bass hitting a top water lure with ferocity? Where did that bass or shark come from? How deep was that fish coming from? If a Great White is cruising 33 ft below the surface and swims up to grab a seal at speed then that fish is experiencing a change in water pressure of 1 atm or 760 mm Hg in just a few seconds. If a small mouth bass is chasing a bait fish school to the surface from a deep water sanctuary then he too is experiencing a water pressure change as the fish goes from deep water to shallow water. Maybe the fish go from deep to shallow water is short hops with stops in between different depths? Like a scuba diver coming up from a deep water dive and having to stop at various depths to decompress. They may stop at 33ft for 20 minutes and then again at 10ft for another 10 minutes or so. So that any gas that was under pressure and dissolved in their blood can be reabsorbed back out of the blood. You won't want the blood gases to bubble out of solution and form air bubbles inside the blood vessels. That will give you the bends and you will die very quickly from that effect. Fish too can suffer from the Bends if you yank them out of deep water into a very hot day. Not only is the pressure released but the fish is heated up by going from very cold deep water to very hot air. To save the fish you would have to return it back to the cold deep water quickly before it develops the bends.

I have found that fish seem to move more shallow when it's a cloudy day or the winds create waves on the water's surface. The waves prevent the sunlight from penetrating the water as deeply was when the water's dead calm. When it's windy and wavy a lot more of the sun's energy is refracted and reflected back off the water and does not penetrate the water as easily. Fish definitely do use contrasting lighting to help them hide from predators and to also hide from their prey fish. Bass or crappie often can be seen stationed in the shallows under a dock or next to a standing timber waiting for some prey fish to swim by. They use the shady area to conceal themselves much like a LION hides in the weeds.

And many smaller creatures rise up and sink when the sunlight conditions change. Copopods and Rotifers are two that do this. And Algae needs sunlight to live. Submergent weeds don't grow in deep water that has little or no sunlight penetration. Clear water lakes have deeper weed beds than murky lakes.

The sun drives all the life on Earth. The sun also drives Earth's weather. The sun heats the earth and make the air rise creating winds. Differential heating of the Earth creates different temp and pressure zones which creates the winds and the changing pressure conditions.

I don't think that just one factor effect the fish but that the total combination of all the factors works together to make the fish do what they do. It's hard to separate out just one factor that we can key in on. Some use the barometer to help them predict the weather. And then they use the changing weather conditions to try to predict what the fish are going to do.

I have had days when I caught lots of fish on a bright sunny day but those fish were deep fish. Then on cloudy days the fish may be only 10ft deep and suspended. Still other times the fish will be in 7 ft of water. It depends on the clarity of the water and the amount of sunlight hitting the water.

Most fishermen in the past fished the bank. Still today you will see 80% of the fishermen in boats along the banks. The others are out fishing the deep drops and other deep water structure. Point is that fisherman these days are a lot smarter and better educated that in the past. We have better tools these days. Side scanning sonar, gps and other big boys toys to use to help us in our fishing. Topo maps made from sonar/gps surveys and sold commercially have helped the average Joe become a better fishermen.

As Old Buck Perry always said. 90% of the fish are in only 10% of the water. The trick is to find that 10% area. Buck said that if you can find a area that has deep water closely connected to shallow feeding areas then you may have a good spot. I have found that to be true. Fish move around in the lake. They don't stay in one spot all day long.

Ask anyone that has ever scuba dived in a lake with big bass and they will tell you that the big bass are found near structure in the deeper water. I personally have seen big 8lb bass just cruising around the lake bottom all by themselves. The same day I saw a big school of 3lb to 4lb bass swimming around this submerged building in 40ft of crystal clear water. The same day I observed huge sunfish guarding nest on a sloped area in 20ft of water. This same area hold big schools of smaller sunfish that were suspended 20ft down in 40 to 50 ft of clear water. The funny thing was that these fish were relating to an old ice box or refrigerator or some other type of appliance that was sitting on the bottom on this rock quarry. Someone had dumped this appliance off the side of the cliff. The fish were suspended right over the top of this area not too far off the seep cliff walls. Only having about 30 minutes of total bottom time that day I could not stay and observe the fish for long. Everyone should have the experience of diving and watching their favorite fish in their own environment.

Some other things that happen in the water that effect the fish when the sun rises and sets. The amount of chemicals rise and fall as plants perform photosynthesis. The pH of the water around these underwater plants changes as Oxygen and Carbon Dioxide Levels change with changing light conditions

Many small floating algae are effected by changing light conditions. The zoo plankton that feed on the algae changes positions in the water column throughout the day and year based on the light conditions. In fact the base of the food change is effected strongly by the sun's position in the sky. It only follows that the top of the food chain species are as well.

Regards,

Moose1am

My Background is in the Sciences. I have a degree in Environmental Science and have been in the Air Pollution Control Field for over 20 years now. But I have been fishing for over 45 years.

[flippindrew]

All I know is, when I see a low pressure day coming I hit the lake hard cause those are generally my best days. High pressure (bluebird) days have never been very productive for me.

[Bonefish]

From your reply to one my post eariler in the year, I thought you must be a scientist in the field of Biology or Zoology. Thanks for a great post and sharing your knowledge. I have a degree in Biology and have worked as an educator in the health feild for 35 years. I also appreciate these discussions because we can always improve our fishing by learning from each other. Don't make fun of me when I misspell a word or don't use the proper grammer from time to time. I seem to be regressing back to my childhood and bad habbits.

[EJHick]

Great post and very informative. What book are you referring to when talking of Buck? Sounds like a good book to get a hold of to understand completely the actions of bass. Now I have a question for you, I understand fish go deep given low BP (high skies), no wind, clearer water, etc. Now in factoring in the dissolved oxygen content for certain layers of water. I beleive that is a major factor, but different people have told me different things on where they stop going deep..some say 4 DO some say 7 DO, what is your stance on this? I like to fish no deeper than water that has 5.5-6 DO in it. Take for instance Nolin, right now I would fish no deeper than 20' given there is 6.1 DO at this level. And it drops almost 2 DO in 10 feet.(http://www.lrl.usace.army.mil/wc/wq/nrrtext.html)

So with the dissolved oxygen content, where are you most likely to say there is too little oxygen in the water for fish to be there? Thanks and again great info.


Eric Hickman Jr.

[Moose1am]

Hi Eric:
Fish require dissolved oxygen to function. Just like humans almost all animals require oxygen to process food and to function. Only certain bacteria utilize other chemicals for life other than oxygen. Think of the deep sea vents that are teaming with life around hot water vents that spew forth huge amounts of sulfur compounds.

The amount of Dissolved Oxygen in the water various over time. Oxygen interfaces with the water's surface and is dissolved into the water from the air. The higher the air pressure the more oxygen that gets pushed into the water. This is the law of Partial Pressure. On high pressure days there may be a little more DO in the surface waters.

Water also takes up more oxygen when it's mixed or turbulent. Like below a water fall there will be much greater oxygen in the water at the bottom of the falls. Or if water is swiftly flowing over a Rockey stream bed and there is a lot of turbulent water.

Most game fish require at least 5 ppm DO in the water and the proper pH. A good rule of thumb is the pH must be between 6 and 8. Fish can live in higher pH waters but they will not function as well. pH 7.0 is neutral. Waters with a dissolved oxygen content of 4.0 or lower may not hold many game fish. There may be other reasons why fish don't go below the thermocline in the hot summer months. H2S gases can be release from bacteria in the lake's muck during the hot summer months. H2S may be poisonous to the fish so they may tend to avoid water with even a trace of H2S.

Another way that Dissolved oxygen gets into the water is from Photosynthesis. Living plants (green plants mostly) when exposed to sunlight create sugars and take up CO2 and expel O2 into the water.

Light penetration and water color or turbidity determine just how deep sunlight can penetrate into a lake. Muddy water has very little underwater weed growth. Take KY lake. Over the years it's clearer up a lot and underwater weeds have began to grow. In the strip pits I fish here in Southern IN we have a lot of pond weed and Eurasian Mil foil growing to depths of 7 to 10 ft. Patoka Lake is an example of a relatively clear water lake in IN. There the weeds grow to depths of 10ft or so. As the amount of sunlight fall off and the QUALITY of the light begins to fade the amount of underwater plants covering the bottom begins to thin.

Now lets talk about how Dissolved oxygen gets spread throughout a big lake. We know that DO gets put into the water at the surface and from streams running into the lake in various spots. We also know that cold water holds more oxygen than hot water. We know that Hot water is less dense than cold water so it floats on top of the colder water. Colder water being more dense sinks below warmer water.

It's fall right now so lets start here. This time of the year the lake waters are cooling down. The surface water get cooled at night and warmed back up a little during the daylight. But with each passing day the amount of cooling exceeds the amount of heating and eventually the water's start to cool down from the hot summer time temps. A thermocline that divided the lake vertically is now no longer there. We call this the event Turnover. That is when the surface water cool down to the same temperature as the bottom waters and the lake is free to mix vertically. At this time of the year, Fall, the lake has plenty of dissolved oxygen in the lakes bottoms.

Also remember that some lakes (Oligotrophic) lakes that lack fertility and nutrients in the water will NOT loose the oxygen in the lakes bottom waters, Hypolimnion. That is because there is no food for the bacteria at the bottom of the lake to eat. Therefore no bacterial growth occurs and the bacteria are not consuming the oxygen in the lake's bottom waters. On the other hands a EUTROPHIC type lake that has lots of nutrients (Potassium, Phosphorous, Nitrogen will hold a substantial bacterial population at the lake bottom and these bacteria will have plenty of food to eat. They will consume the nutrients and use up the oxygen in the lakes bottom. When the lake is stratified the amount of oxygen in the lake bottom will be lowered to almost zero at times. But this only occurs in Eutrophic type lakes in the warmer months of summer. After the lake turns over the dissolved oxygen at the surface is free to mix with the bottom waters and vise verse. When turnover occurs on a eutrophic lake you may notice a H2S smell that reminds one of rotten eggs.

Now back to the mixing of the oxygen throughout the lake. When Winter approaches the cold northern winds arrive and these winds drive the lake into a white capped mess. These winds create long waves that travel down the lakes surface and then run into the windward banks. There the water piles up and dive down under the surface bouncing off the bank and then traveling in the reverse direction under the surface. These lake currents are setup when you have a long time period of high winds coming from one direction. The underwater currents help the lake to turn over and to mix after the lake turns over. Energy is required to make the bottom waters mix. The winds provide this energy in the form of lake currents. Also these backwards currents that begin at the windward banks can be great fishing spots if you can control the boat. Fish will wait just off the bank waiting for food to be delivered to them by the current.

Algae that float freely in the water is carried by the currents and if the algae can gather sunlight in the water it will be producing dissolved oxygen during the daylight hours. Plants also require oxygen when the sun is not shinning so they use up oxygen at night and give off CO2. During the day this is not the case.

Now back to your question about the fish and the DO levels. Fish at this time of the year (POST TURNOVER) are free to roam the entire lake from the top to the bottom. New food source open up on the lake bottom now that there is enough DO down there to support the fish

A bass or game fish needs more dissolved oxygen than a catfish. Rough fish can survive with less DO than game fish like Largemouth Bass, Spotted Bass, Small mouth Bass and Crappie etc. Fish normally swim among the plants during the daylight hours. There they find food, protection from bigger fish and lots of dissolved oxygen when the sun shines brightly and penetrates the water deeply. Blue and green light penetrate the water more deeply than red wavelength. Longer wavelengths get filter out sooner than shorter wavelength. They have less energy to penetrate the water with. Small particles of dirt and chemicals filter out the red wavelength light faster than the blue wavelength light waves.

Finally as old man winter arrive the fish are found in the deeper areas. This is because water when it reaches 4 deg C is at it's most dense. Normally water gets denser as it cools down. But due to the nature of the water molecule it gets lighter after it cools down past 4 deg C. Water at 3 deg C will rise above water at 4 deg C. And when water at 0 deg C freezes it will float to the surface. If not for this physical nature of water the lakes would all freeze from the bottom to the top and kill all the fish. Now the 4 deg C water will be the warmest water in the lake and it will be the most dense water and end up on the very bottom of the lake. When there is ice floating on the lake and it's freezing cold the fish will seek the warmest water and a this time that's on the very bottom of the deepest part of the lake. Remember that dense water will sink to the lowest part of the lake.

I think your question was about the summertime fish. Well that's where the lake is stratified if it's a deep lake. If it's a fertile lake like we have here in the Midwest it will be fertile too. Fertilizer runs off from the farmers fields and into the ditches and then into the streams, creeks and then reaches the rivers and reservoirs. Fish in the hot summer months can't really go below the thermocline. They may suspend down right above the thermocline in about 20 to 10 ft below the surface. It depends on where the thermocline is and the amount of DO below the thermocline. Only after the lake stratifies and the bacteria have time to deplete the DO in the hypolimnion will the fish not be able to use the bottom waters of the lake. Then the fish are restricted to the areas above the thermocline. Luckily most fertile lakes have lots more color to the water and filter more of the sunlight out. Clear water lakes with rocky bottoms may have deeper weed bed growing on the lake bottom. The fish will hide in the weeds where they get life's necessities. Food, shade from the sun, Protection from other predators and lots of Dissolved oxygen. Even the pH of the water can change in the weedy area due to the uptake of CO2 by the weeds. CO2 forms with water making a mild acid solution. Rain water is slightly acidic naturally due to this fact. Limestone in the stream beds and lake bottom helps to neutralize this acid and buffer the lake's water.

Bottom line is this. During hot summer months fish above the thermocline or in the weeds. An underwater spring that bubbles up from the lake bottom can add clean water, nutrients and dissolved oxygen to the water there so fish may be able to use this area at times.

After the lake turns over the entire lake is used by the fish and there is not Oxycline to keep the fish in the upper water levels, Epilimnion.

The amount of dissolved oxygen in a lake can vary from day to day and from hour to hour as the sun moves across the sky and as clouds block the sunlight from penetrating the waters surface.