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3. UV spectrum and trout, Page 3

Interesting... So, counter intuitively, those same "whiteners" and "brighteners" that make clothing and such glow in black light actually make objects duller to eyes that perceive UV? More than a bit confusing at first, but makes sense if you think about it...:)

I can see clearly now.

What is not intuitive is the appearance of a mayfly in the UV. Take, for example, two Gray Drakes. Focusing on the wings, we see in the first - Siphlonurus rapidus - a very marked banding of light and dark (more UV reflective and less UV reflective)


What I find intriguing, is that the old Gray Drake dry pattern found in Trout by Bergman in 1938 has reproduced the UV wing banding - not visible in visible light - through the use of a teal wing and grizzly hackle.

Siphlonurus occidentalis has less pronounced wing banding in the UV.

but it is quite beautiful, IMO.

Hmmm... Very interesting, Reed. Perhaps you are pointing out the reason behind why old timers believed natural dun capes work better than dyed? Your suggestion of using veriagated materials that reflect visible light to mimick the the look of certain UV reflecting materials opens up a whole new can of worms...:)

BTW- What process is being used to show reflected UV as visible light, allowing us to see it? Am I right in assuming that this isn't what is actually seen by fish & game but rather pointing out that certain objects reflect UV differently?

You said:


Those photos were taken with a Nikon D40, Ludwig Meritar triplet lens, and a UV bandpass filter.
Now I use a Lumix GF1 modified for full spectrum (the internal IR cut filter replaced with quartz), a lens such as the Meritar (the fewer glass/air interfaces, the less loss of UV) and UV bandpass filters of my own design. These filters only allow wavelengths from 320nm to 400nm to pass to the digital sensor. The digital sensor is custom white balanced through software and a PTFE standard.

The camera is recording the same UV wavelengths as the fish's retina; however, the fish's retina doesn't have all of the glass and filters, so the fish captures many times more UV. After dark, when the trout's retinal rods are in use, a single UV photon can produce a message to the brain. It would probably require twenty photons to activate the sensor of the camera, due to loss through the camera lens and filter, the quartz, and the Bayer filter.

OK... But how are we seeing it?

It is somewhat the same as IR photography, in that the camera translates the invisible wavelength input into a visible output. It can be done with film as well as digital sensors. Basically, you need pixel elements that will be activated by, for example, 365nm UV, and output on film or a digital file as, say, 550nm orange. The more intense the input, the brighter the output.

Obviously, the trout's brain records UV differently; the trout had only UV vision at birth and the synapses were established. As fishermen we only need to know the relative UV reflectance of the trout's prey's markings and we can approximate the insect. BTW, trout, like many other creatures, have maximum UV receptivity at 365nm, and probably nothing below 340nm. So, the range is narrow.

[Humans also had UV vision while young, but the yellow pigments in the lens of the eye now blocks it. However, when the lens is removed in cataract surgery, we can see in UV once again.]

That's what I needed cleared up. Thanks for the detailed answer, Reed. In fact, thanks for all your contributions to this topic. You are very knowledgeable and have made this thread a great one. Do you mind sharing with us how this came about and what spurred your interest?

It is hard at this date to recall the sequence of events. Probably it was encountering research done by Craig H. in Canada on ultraviolet vision in trout. That got me thinking about how trout might use it. I wrote a few notes on The Contemplative Angler on the subject; those were well received. Instead of writing an article for one of the FF magazines, I found myself learning UV photography and writing a book - The New Scientific Angling...

However, in writing the book I discovered that my fishing vest was way too UV reflective -- which made me think about camouflage. I found that all the camouflage I tested - both military and hunting - was wrong in the UV; so I applied for a patent on Camouflage in the Near-Ultraviolet, and spent the rest of my time developing UV camouflage (see UVR Defense Tech to protect the modern military.

So, that's how I did it. Except, I also needed good UV bandpass filters, so I designed some, and now make them as well - UVROptics.

Very cool, thanks for sharing!

Yes Reed very cool. Thank you for your detailed and informative posts!

OK... I'm intrigued. I guess the field has developed further.

Not sure how far UV penetrates in most FW's though. Talking about UV penetration on SW reefs is another story. My understanding is that UV doesn't penetrate far in FW, which would mean it doesn't scatter far either, hence it being functional only in very shallow waters -i.e. larval fishes picking out zooplankton. That said, I've purchased your book.

Paul,

If you wish to believe that UV doesn't penetrate far in freshwater, you are welcome to such a belief. I won't therefore confuse you with facts or studies. Had you asked for such, I would have been happy to provide them. :)

Whoa there, Reed. Please don't take offence, but the regular contributors here (Paul is one) have seen a lot of claims posted over the years that haven't stood the test of time (or the facts). Discourse is what this forum is all about and the reasonable questions posed by Paul can hardly be equated with the desire to "believe" the earth is flat. I can assure you he loves to be "confused by studies." He did mention he was purchasing your book, after all (as will I and probably many others here)...

Pax

Please feel free to cite the facts & studies, Reed. Those are always well received here, by Paul and others.

A quick Google search pulled up a relevant link (questionable source, though) suggesting that UV can travel through water much farther than other visible wavelengths. Also, here's a link with some relevant physics papers I don't have time to look through, but maybe somebody can. I'm sure Reed knows some much better sources.

It would be really interesting to see some underwater photos of aquatic insects shot in UV at various distances. Of course, that's much easier said than done and paid for!

And at the surface in the trouts window too. Reed mentioned the problem of clothing. I wonder how UV is affected by the prismatic effect of Snell's Circle?

Interesting question Kurt, which led me to this question: I wonder if the “discriminating” trout (educated) keeps the insect within Snell’s Circle as a means to study and verify?

Yes, Goddard believes he has proved that when a fish drifts back with the floating object held at a certain angle, it is doing just that. This behavior is most noted in bright light when a critter in the middle of the window would be a black silhouette. Un-pressured fish will hold in the current and as the object hits the Snell, that brief look will trigger the response to take or reject. An educated (pressured) trout will do the "drift back" for a longer inspection in the hope of avoiding "sore mouth." :) The really smart ones will even turn to follow a little to verify further by changing the background or backlight. Those are the really tough bastards! :)LOL Pretty compelling evidence...

Below are some studies on UV penetration of freshwater. Equations have been developed to estimate the depth of penetration based upon such criteria as DOC (dissolved organic carbon), DOM (dissolved organic material), and POC (particulate organic carbon).

The major emphasis in UV studies of water penetration is on the UVB wavelengths (280nm to 320nm) which are harmful to aquatic life. UVB, however, is a small percentage of the solar UV, which is greatest in the 360nm to 400nm range. Trout's retinas have peak reception at 365nm. Here is a spectrum of solar radiation:

Notice the sharp drop in the UV.

Studies include The Penetration of UV into Natural Waters

The attenuation of solar UV radiation in lakes and the role of
dissolved organic carbon

Effects of Temperature and Ultraviolet Radiation...

Water Column Optics and Penetration of UVR


P.S. - I realize that the studies shown are heavy trudging. If you wish an easier way to satisfy yourself that UV is penetrating to the bottom of your local river simply tie a cinder-block to the foot of some neighborhood urchin, hand him a waterproof camera and a piece of fluorescent orange tape, tell him to photograph the tape when he reaches the bottom and chuck him in to your least favorite pool. Did I mention tying a rope to him? When you pull him out, I am confident that the photograph will reveal the tape as orange, which means that UV wavelengths penetrated to the bottom of the pool and excited the fluorescence. Sometimes you won't get a good shot on the first try, so repeat as necessary.

How about an obnoxious fishing buddy in place of the urchin? I can think of one that would need at least a half dozen or so attempts to get the photo that would make me happy.:)

Sorry, couldn't help myself (in case you're reading this)...:) Thanks for the data and links, Reed!