The New Scientific Angling - Trout and ultraviolet vision

[mlw]

I have been reading an interesting new book:
The New Scientific Angling - Trout and Ultraviolet Vision
the author (Reed Curry), also has a blog where you can read an excerpt.

The author makes some useful distinctions and debunks some applications. The first distinction is between reflected UV light (for example how a bug or baitfish appears to fish), and fluorescence - materials that give off a visible color when hit with uv light). His primary interest is in how insects and other trout food appear to fish capable of percieving UV light (we don't - the lens of the human eye (and most mammals with the exception of whitetail deer) has a yellow filter in it. So if you can see a glow of some color, that material is fluorescing, not reflecting uv. Fluorescing materials may be useful as attractors for sea run fish, but there are no fluorescing food items for trout.

Daylight contains about 8% UV, but a higher percentage at dawn and dusk, when trout are most actively feeding.

Many classic trout fly patterns contain feathers or fur that do reflect UV light in a realistic manner, similar to the wings of common mayflies. Many birds and insects use uv marking for mate selection, etc.

He also debunks some common applications of "UV", such as using Titanium oxide or zinc oxide (both of which absorb uv).

Hareline provided materials for the author to test

Very interesting book, which sheds new light on how fish perceive flies.
Michael

 

[Irishrover]

I would be in deep trouble for a pun like this " Very interesting book, which sheds new light on how fish perceive flies."

Part of what I am getting here is stick to the basics. Fur and feathers because of the natural uv reflection. Makes sence because some of those patterns have been producing for years. I have a tendency to add crystal flash because I can see it, so I made the assumption it would be easy for the fish to see. Guess I might be wrong about that. I like to add crystal flash to hare ear and pheaseant tail nymphs, and wooly buggers. Think I'll tie 50% natural and 50% with crystal and do my own non scientific study. Interesting information Michael.

 

[mlw]

Yes, I think many of the popular patterns, whether by natural selection or not, tend to also mimic the uv reflective quality of the bug in question. For example Caddis fly wings are hairy, not uv reflective, therefore a dark silhouette on the sky - as is the deer or elk you tie them with. Similarly that white calftail or antron post on a parachute dry may also reflect linear uv patterns similar to the faceted wings of mayflies. So conveniently, at dusk when a white post will help me see the fly, in the increased uv light I don't see (it's getting dark) but trout do, the post reflects uv light like the natural insect (a yellow post, however, would appear almost black to the trout). Pearl Flashabou is highly uv reflective (and prominent in a Posse Bugger), silver wire also. I think the thing to keep in mind is that if one is trying to imitate an insect food source, a subtle use of flash and uv materials is often more likely to meet with success than a bold touch - and that uv is part of what trout see, particularly in low light or deeper water, and we are the visually impaired.

I have been tying some experiments too, adding a small pinch of UV Ice Dub to Hare's Ear or possum dubbing, etc.
Michael

 

[FishFinger]

I suggest you also read the book "What fish see", What Fish See by Colin J. Kageyama.

There are many factors to be considered, many not often addressed when directly comparing the theories of UV verses true florescence.

I have my doubts regarding a a UV component to aquatic insects. Over the course of natural selection bugs that might glow would have been found and eaten long ago, while those that go "undetected" are more likely to survive and procreate.

Remember we're basing theories on creature with brains smaller than peas. How and what they see are a lot different when considering brain mass alone.

I have a set of colored lenses that help to mimic the resident color of several water conditions. What they do is illustrate the effects of color shift. You don't need a black light to identify the florescence nature of a given material. Filtered light is a truer example of florescence verse resident color. ( The actual environment that fish dwell.) When it comes to "materials" not all that claim to be florescent actually are. It depends on pigment. Lack of pigment would not preclude some UV potential, rather based on resident color and distance shift the objects color will move towards black.

Sorry if seem to be rambling, After merging years of color theory (via oil painting) and what Dr K. wrote, it was a Eureka moment. As simple as the 3 primary colors mixed to create 3 secondary colors, then onto the effects of compliment colors of those 6. There after considering the effects of the waters resident color and color shift at distance;, we can begin to "see" what a fish might "see" if it's brain were as large and complex as ours. However, they are not; which has to suggest some diminished capacity.


I propose that.... If you cast a flat red corky into green water, that after a few feet of depth the red will turn black ( green is reds companion color, companion colors never change the resident color except to lighten or darken it). A florescent pigment will tap into neighboring light waves, making it brighter at both depth and distance.

Here's one theory in a nutshell... ok a large nutshell, sorry about the corky analogy...

You cast your flat red offering and it's noticed by a fish. initially it's being recognized, perhaps as a contrasts; most likely black against the resident environment. It's brain tells it to investigate and it targets the object. A black object. As the fish closes in the object changes from black to red. At that moment the fishes brain has to decide if that is the same thing it was after and if it should continue to pursue.

You cast a florescent red offering in the same water, depending on the distance that corky will appear red for a longer period mitigating the time a fish has to "rethink" it's actions.

 

[mlw]

Reed Curry is not so interested in fluorescence, but in how uv reflectance plays a role in trout identifying prey. We can't see uv light or reflected light, with or without a black light, so uv photos of insects (or flies, fly tying materials), are all we can go on. Many birds and insects use uv reflectance as identification for sexual selections, a healthy bird will have more reflective feathers, thus be a fitter mate, etc. The reflectance comes from the structure of the insect body, wing, etc (thin layers of translucent chitlin that make up the exoskeleton, wing, etc, not fluorescing pigments). The same is true of feathers, it's the structure of the feather that reflects the uv light, not pigment (although darker pigments will absorb the uv light rather than reflecting it). Deeper water often has a uv ambient glow from uv light rays being refracted by stuff in the water, in that situation, a red lure will appear black if there is no red spectrum visible light getting to it, and a uv fluorescent lure would fluoresce red from the uv light, and the uv reflective lure (or baitfish, etc) would reflect the uv light as uv color. While there are prey in the ocean that fluoresce, there are few, if any in trout habitat. But many insects target dawn or dusk to reproduce, so it makes sense that reflecting and observing uv light would play a role. (and many mayflies have large and complex eyes adapted to uv - see Arlen Thomson's discussion of male PMD eyes in Bugwater.)

Fishfinger, color shift with depth etc also are going on re visible spectrum, just we can't observe the uv portion. UV penetrates deeper than the longer wavelengths, like red, which gets knocked out first. Within UV, there are "colors" - UVA, UVB, etc corresponding to different wavelengths.

You cast a florescent red offering in the same water, depending on the distance that corky will appear red for a longer period mitigating the time a fish has to "rethink" it's actions.

- I can agree with that, but for purposes of fishing that is based on imitating the appearance of food items (say trout, rather than steelhead) , the question would be "what do salmon eggs look like under a higher concentration of uv light and a lower concentration of the red end of the visible spectrum?
Food for thought
Michael
Michael

 

[FishFinger]

I applaud you for your thought provoking implications and applications of UV.
All kidding aside you've made me stop and rethink a lot of things.

The notion that 'brain" size or development isn't even in play. UV perception is based rods, cones and eye structure.

"Insects have even more different types of eyes and vision systems than
the less advanced animals we've considered. Many insects need to see
in three dimensions while flying at high speed. Indeed, winged insects
have better vision than wingless ones. The variation of eye size,
resolution, and overall optical design in insects is also great.
Many insects see a wider spectrum of colors than humans do. Their
color vision spectrum may vary from ultraviolet, in the case of the
bee, to near infrared, in the case of some butterflies, and beetles.

Bee eyes sense polarization of visible light in the sky and also have
sensitivity to UV light. They seem to see blue colors best, but they
also see ultraviolet colors beyond the blue colors which humans see.
Don't forget that a yellow flower may have markings that reflect or
absorb light in the UV region. Flowers may also have narrow-band color
reflections that communicate to bees and other animals the type of
plant it is. Bees' extended range of color vision helps them to locate
flowers and food to function in their survival and growth."

Insects have "sight" in to the uv range.

Ultraviolet colour perception in European starlings and Japanese quail

"Whereas humans have three types of cone photoreceptor, birds have four
types of single cones and, unlike humans, are sensitive to ultraviolet
light (UV, 320-400 nm). Most birds are thought to have either a
violet-sensitive single cone that has some sensitivity to UV
wavelengths (for example, many non-passerine species) or a single cone
that has maximum sensitivity to UV (for example, oscine passerine
species). UV sensitivity is possible because, unlike humans, avian
ocular media do not absorb UV light before it reaches the retina. The
different single cone types and their sensitivity to UV light give
birds the potential to discriminate reflectance spectra that look
identical to humans."

Many (some) birds can also see into the UV range and their plumage can and does have UV reflective attributes.

So I suppose it boils down to make up of an eye and how it's processed; species specific.

 

[overmywaders]

Fishfinger,
Evolution actually favors insects which wear ultraviolet markings. Mayflies, for example, have only one day to meet a mate and start the next generation. Therefore, it behooves them to find the correct species and gender for their only moment of whoopie!

How can they identify the senorita who will make their life complete? At dusk and dawn (the crepuscular hours) the percentage of UV light increases over visible light; hence, UV markings of gender and species make the most sense. We know that mayfly duns use UV light to find the stream of origin - though the reflection from wet roads is often similar enough to cause fatal errors - just so, they use UV markings on wings and bodies to distinguish their kin. Doesn't it seem sensible that trout, which also have UV vision, would consider my #14 Adams - tied with a UV reflective fur - a safer dinner selection than yours which looks identical to us but doesn't have the UV reflection of the hatching flies?

BTW, even humans start with UV vision; however, since we don't have the stem cells in the retina which allow trout to regenerate cones and rods throughout life, we need to develop a filter in the lens of the eye to prevent damage from UV rays. Deer, OTOH, lack this filter, but spend most of their daylight hours bedded down with eyes closed.

regards,
Reed

 

[mlw]

Interesting stuff guys.
If you look at closely at Pale Morning Duns, the males have big orange(uv sensitive) eyes (a reason to use orange thread when tying pmds), whereas the females don't, as the males search for their mates against the sky.
A few ideas to test:
In lower visible light levels(higher percent uv light), white feathers or fir, silver wire or pearl mylars etc will reflect more uv light than yellow feathers, gold wire, etc. Here is a fly that ought to have a bright UV display, a Usual (orig Fran Betters), which is just thread and snowshoe hares foot (any prey that seeks camouflage in the snow is bound to be quite uv reflective, otherwise it would stick out in low light levels, a fact soon fatal)


In water, light is scattered by suspended particles, and a day or dusk that looks dark to us, the water may have a uv ambient glow - picture a lighted dirty aquarium with a bluish tint - and in such a situation a dark non-uv reflective fly may be just the ticket - that black wooley bugger, stonefly, leech etc, may standout. Further credence to the dark day, dark fly - bright day, bright fly theory, although perhaps it should be modified to dark day, black or white fly, bright day, bright (visible) colors.

UV visibility may be a good argument for wings on flies, whether wet or dry, a classic winged wet (like this Mckenzie, tied from Ray Bergmen's "Trout"):

It may not look very imitative to us, but if our vision is a little limited, we have superb pattern recognition; which has to be much more sophisticated than a trouts. They also often have limited time to decide whether that chunk of something floating by is worth tasting or not. Perhaps many of our traditional wing materials aren't so bad at imitating an insect wing - which could easily be one of those "hot spots" or
"pattern matching criteria". Zelon or Antron, etc are pretty reflective too, but perhaps the black/white markings of wood duck, mallard flank, turkey, partridge, etc are more natural.

In fly tying and fly fishing an awful lot of "field experiments" have taken place so there is an interesting intersection here between new science and old technique.
Michael

 

[FishFinger]

Honesty I have been trying to find out what things would like like if I could see in UV.

I'd rather consider seeing our full visual spectrum plus UV, but I suppose to start it might be best to see uv only.

I decided to start here.... YouTube - Converting Full Spectrum Camera to Take UV & IR Photos (turning a full spectrum camera into a UV/IR only camera)
What I would expect to see would be more contrast and a blue hue. pretty much like the end of the video shows.


here's a good example of the contrast. YouTube - UCP Camouflage in the Ultraviolet


Here too there is major contrast until it is treated with a non uv reflective substance. YouTube - A Commercial Ghillie Suit in visible light and then UV


Both of these examples are showing visible light then UV only, not the full spectrum; plus uv


This video is pretty funny just using a black light and a full spectrum filter. Again a lot of contrast.

YouTube - Using UV with IR Cameras

My interest in UV has been peaked and now even more theories abound... Such as that UFOs, entities, poltergeists, and ghosts may also hang out in the UV spectrum. I potentially propose that Bigfoot might dwell in the UV too. I mean just because we can't "see" it dosen't mean it can't exist. I think I need this camera...

We often take different roads that bring us to the same place. The old science of contrast and movement are still in effect. At this point in my "learning" I can accept uv may indeed play to enhances contrast; if the fish I target are able to see the difference.

And I hear you smell bigfeet long before you'd ever see one........

I am done hijacking my own post: I'll return this thread to those with more common sense than I have.