Awareness of your shadow on the water

**Silver Creek** · 12-03-2009, 12:53 PM

[quote author=AaronJasper link=topic=3825.msg29659#msg29659 date=1259855110]
Very nice diagram and explanation. I will look at how the shadow is bent this weekend. So if shadow looks to be 30 feet, it could only be 20-25 feet when it reaches the bottom. And the only time that it is straight is if something passes directly overhead like a fly line or an indicator... Correct?
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Well...... Maybe.

The location of the shadow of a fish is usually at a different location than the fish itself unless the fish is very near the bottom or the sun is directly overhead.

The angle of the sun displaces the shadow of the fish on the river bottom. The displacement is in the opposite direction of the sun from the fish. So if the sun is to the North of the fish, the shadow will be displaced to the South and the amount of displacement will depend on how far above the bottom the fish is holding. Also the lower the sun is in the sky, the greater the displacement.

What the shadow does is to alert us to the presence of a fish. Note the location of the sun in the sky, and the fish will be somewhere in the water along and below a direct line between the sun and the shadow. So if the sun is to the right side of the shadow, I look through the water on the right side below the line from the sun to the shadow to find the fish.

The depth of the fish also changes the size of the window. In the diagram below I have added arrows for the size of the window and the depth of the fish. You will also notice that the angle of the window from the trout's eye is 97.5°. Half of that if 48.75° which is about 45°. At 45°, the distance = r from the center of the window to the edge of the window is exactly equal to the depth =r of the fish. So we can approximate the the size of the window from the depth of the fish. The window diameter is 2r or about twice the depth of the fish.

Note also that the deeper the fish, the larger the window. That means that the deeper the fish, the closer the edge of the window is to you and the lower you must be to stay under the fish's vision.

The size of the window also compresses the image of the outside world into a very limited space that gets increasingly smaller as the fish gets closer to the surface. You can now understand why, when the troutis feeding selectively and holding just under the surface, we can get very very close to the fish. His image of us is limited by the window size as well as the 10° line.

**AaronJasper** · 12-03-2009, 06:36 PM

Thanks for the great information. The formulas are easily understandable and the graphs were very good. This will give me something more to throw into my approach to the stream. I think that this is an area where every angler can improve upon greatly. Thinking about these things will even help a newer fly fisherman put him or herself in the best possible position to be successful.

**Fontinalis** · 12-08-2009, 12:04 PM

Ray Bergman once wote about having the sun at your back stating this was to your advantage. Furthering reading Ray stated that the fish had the sun in it's eyes and it visabilty was greatly reduced. Just think of how your eye sight is when the sun is in your eyes. I have tried this experiment and it has worked for me. Now I do believe in shadows do alert fish to the presance of a predator and causes them to flee. I have done this as well on a smaller portion of the upper Willowemoc and spooked the day lights out of a few fish that I could not see while wearing polarized sun glasses. I think this is an interesting topic and am only stating my experiences on stream. I do believe that every ones input that I have read so far is valid and do not doubt there encounters.

**Silver Creek** · 12-08-2009, 01:29 PM

[quote author=Fontinalis link=topic=3825.msg29802#msg29802 date=1260288273]
Ray Bergman once wote about having the sun at your back stating this was to your advantage. Furthering reading Ray stated that the fish had the sun in it's eyes and it visabilty was greatly reduced. Just think of how your eye sight is when the sun is in your eyes. I have tried this experiment and it has worked for me. Now I do believe in shadows do alert fish to the presance of a predator and causes them to flee. I have done this as well on a smaller portion of the upper Willowemoc and spooked the day lights out of a few fish that I could not see while wearing polarized sun glasses. I think this is an interesting topic and am only stating my experiences on stream. I do believe that every ones input that I have read so far is valid and do not doubt there encounters.
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I wonder if what Bergman was observing was the same thing that we see when we take a photo facing the sun. The objects are in silhouette and the discriminating features and colors are in shadow. Essentially, the fisher is camouflaged, since the background and surrounding objets are also silhouettes. So the fish has a problem discriminating, when we stand still and our shape overlaps other shapes. It has no color or color pattern to tell one object from another overlapping objects. The main way of telling one object from another is motion.

I don't think that your visibility is any less. That is determined by the window. It is that the ability of the fish to discrimate through color ane pattern is less.

The fish has the advantage of going deeper to decrease light levels. When at depth, the window is larger.

So I think that whether this strategy works depends on how deep the fish is, the angle of the sun which determines shadow length, and how fast you move. Whether you are in silhouette or not, I believe the fish can still detect motion.

**Fontinalis** · 12-08-2009, 02:57 PM

Not always true. You see the Trout may not have the case to go deeper and the glare is actually what it is. Now if the Trout does go deeper a few things can change drastically. The angle entry of light in the water could amplify thus making the Trouts vision glared or could com the light down and give visability back to the Trout to spot it's subject in the window. Also keep in mind we also have to talk about water clearity which again would either aid or hinder the Trouts viewable window as well.

**Silver Creek** · 12-09-2009, 12:54 AM

[quote author=Fontinalis link=topic=3825.msg29806#msg29806 date=1260298641]
Not always true. You see the Trout may not have the case to go deeper and the glare is actually what it is. Now if the Trout does go deeper a few things can change drastically. [b]The angle entry of light in the water could amplify thus making the Trouts vision glared or could com the light down and give visability back to the Trout to spot it's subject in the window.[b] Also keep in mind we also have to talk about water clearity which again would either aid or hinder the Trouts viewable window as well.
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I intend no disrespect but I don't understand. Perhaps you can go into more detail. My questions and my understanding follows.

Can you explain how you think the angle of light entry changes since the sun's angle above the horizon is fixed whatever the fish's depth? The amount of light entering the water is greatest when the sun is directly overhead at 90 degrees to the water surface. And yet that is when there minimal shadows are cast, and when surface glare is the least.

The depth of the fish does not change the amount of light actually entering the water, it changes the size of the window.

I also don't understand how water increases glare to the fish when they are UNDER the water. And how does your underwater "glare" change with water depth. I believe what causes glare above water is the reflection of light from the air/water interface, ie, the water surface, back into the air. Therefore, underwater glare cannot be caused by above water reflection. There is an water/air interface than can be seen from under under the water that surrounds the window, but since there is no point source of light under the water, there is no "glare from the surface mirror. What we see reflected in this the is bottom of the river.

Above water glare does not cause more glare under the water. Actually, just the opposite is true. The more "glare" or % reflection of light back from the water surface, the less light that penetrates the water surface. So I believe when glare above the surface is great, relatively less light is penetrating below. We know that from experience because when the sun is low in the sky and at an acute angle to the water surface, there is the greatest glare in our eyes and the least light penetration into the water.

By saying that there can be greater light in deeper water, you imply that water does not absorb light. Can you explain that? I've been taught that all water absorbs light, even distilled water. So even in the clearest water there is less light as the fish goes deeper. Water cannot increase the light making it brighter. What it can do is change the spectrum of light by absorbing and scattering light. Water acts as a light filter depending on what is dissolved and what is suspended, but it cannot increase the total amount of light.

**Magnet** · 12-09-2009, 03:44 PM

Silver,
I think Fontinalis was referring to the angle of light, not in a moment in time which would be constant regardless of depth, but rather as a time continuum during the course of a day. Great analysis guys!

**Silver Creek** · 12-09-2009, 04:57 PM

[quote author=Magnet link=topic=3825.msg29847#msg29847 date=1260387894]
Silver,
I think Fontinalis was referring to the angle of light, not in a moment in time which would be constant regardless of depth, but rather as a time continuum during the course of a day. Great analysis guys!
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Got it. The angle does change as time passes. When he said he fish did not have to go deeper to escape bright light, I assumed we were comparing light intensity at depth to illumination near the surface.