Fish Vision: Color Underwater

Now that we know what fish see above the water’s surface, what do they see in the water?  Let’s start with color.  

We discussed in the previous article that water has different optical properties than air.  Water is about 780 times more dense than air.  As light hits water, not only does the light bend, it is selectively scattered and absorbed.  Greater than 75% of the visible spectrum is absorbed within about 30 feet.

Here’s what you need to know and think about.  In clear water, the colors we see as red, yellow, and orange are lost first.  “Lost”, meaning scattered and absorbed.  The colors we see as violet, blue and green reach farther, with blue penetrating to nearly 500 feet.  How far light penetrates on a given day depends on the angle of the sun, the roughness of the water’s surface, and how much sediment is suspended in the water (turbidity).

Light intensity plays a big part in how a fish perceives color. Fishing on a sunny day will allow light from the sky to penetrate much deeper through the water column than on a day with clouds. Shiny colors like silver and gold are less effective when cloud cover rolls in, and can become almost invisible without the sun shining, even in clear water. The reason for this is that they reflect the grayness that is surrounding them, instead of the bright rays of the sun. Casting darker colors (like blues and purples) in low light (whether due to cloudiness, early or late in the day, or water with a high amount of suspended sedimentation) often work best by giving your fly the greatest contrast and silhouette. 

***So remember, as the sun sets (or at sunrise), cloudy days, or in stained water, colors like red, yellow, & orange will disappear the quickest. Blue, violet, and green are seen by fish much better in these low light conditions.

Now, what about all of these shiny materials and UV enhanced materials we see for files these days?  Great question!  Glad you asked.

First, there is some research that suggests that fish can sense polarized light (where we humans cannot separate polarized light from regular light).  Polarized light is unique in that it only vibrates in one plane.  I know, blah blah blah, but stick with me here.

When light is reflected off many nonmetallic surfaces, including the water’s surface, it is polarized to some degree.  Your polarized sunglasses block horizontally reflected light from the water’s surface, permitting only vertically reflected light through…thus reducing glare.

What does all of this have to do with fish vision?  It’s thought that fish that can see polarized light use the ability to help them find food.  When light reflects off of surfaces like fish scales, it becomes polarized.  A fish with polarizing vision can more easily make out baitfish and not lose them in the background of the plants and or rocks in the water.  It is also thought that fish with polarizing vision can see objects as much as three times further away.  AND, polarized light is most abundant at dawn and dusk.  Way back in 2001 a great study was done that showed in Oncorhynchus mykiss (our beloved steelhead), polarization sensitivity may provide these salmonids with an improved means of locating prey.  (That’s as crazy technical as I’ll get in these articles. I promise!) Now, this study was in juvenile fish.  There is some research that suggests that mature salmonids lose the ability to see polarized light.  And there is other research that suggests that salmonids regain that ability for a time when they reenter the rivers and streams to spawn.

Now you understand why many companies that make materials for fly tying are manufacturing “Polar” products.  Steelhead may be able to see them better, from further distances, and in lower light.  And this is how they look for food, at least as juveniles.  Think you might want to use this stuff in your flies?

What about all of this “UV” stuff (UV = ultraviolet light)?  It’s similar and pretty simple.  There is research that shows that colors that fluoresce in UV light are visible and distinct for longer distances than regular colors.  BAZINGA!  UV light is most is dominant on cloudy or gray days.  On sunny days, the fluorescence is much less.  So, under the right circumstances, we can take advantage of materials that fluoresce under UV light to gain a more visible and vibrant presentation.

All of our flies are used to imitate something fish feed on.  And at times, it can help to add in materials that can be seen by fish that can see polarized light and it can help to add fluorescent or “UV enhanced” materials to make the fly stand out.  Of course you must also understand that these enhancements could work against you when chasing fish that are in areas with abundant forage.  Fish key in on “hatches” very specifically at times because they are safe.  It is against their instinct to eat something unusual in those situations because it presents more risk to them.  So, you have to chose wisely for each situation.

Hopefully this gives you a concise little primer on why and when we use the colors and materials we use for various fishing conditions.  If you need more help drilling down your steelhead game…call me!  LET’S GO FISHIN’!