UV got to be joking

UV got to be joking

Martyn White | Wednesday, 26 February 2020

I've recently been watching a wildlife documentary called Night on Earth about the nocturnal goings on in the animal kingdom, and I've been enjoying it a lot. The quality of the low light footage is amazing, maybe soon there will be a consumer level camera that can pick up the lumo lines at night!
As entertaining as it has been, the coral reef episode was what really grabbed me. They were shining a black-light over the corals to show how they flouresce, which also showed how many reef species are also fluorescent. Mantis shrimp, crabs, gobies and lizard fish all displayed fluorescent pigment, all prey species for loads of flats targets.

Being fluorescent doesn't seem like a particularly good survival strategy, but apparently it acts as some kind of sun protection by converting harmful UV light to less damaging visible light, makes sense if you make your living in tropical flats under knee deep. This has a lot of implications for the fly patterns we use, obviously a lot of saltwater flats flies already have touches of fluorescence in them and fluo materials are nothing new. However, having seen the animals under a UV light, I think a lot of flies could be improved by getting rid of hotspots and having smaller amounts of fluo spread through the fly. I think this is probably the reason the Gotcha, for example, is so consistently effective for bones and other species; the fluorescent thread underbody covered by a translucent reflective material that reduces the intensity of the effect while allowing the emitted visible light to be dispersed at various angles along the whole fly, while the non fluorescent craft fur breaks it up when viewed from above.  Other patterns like Dick Brown's Striptease in the picture,with translucent dubbings on fluo thread create a similar effect.


Almost all the flies I tie for myself contain fluorescent material, not just for salt water. I don't think it's necessarily that most of the colours are "bright" like the globrite colours and, in fact, my favourites are the materials that don't look fluorescent until you put the UV torch on them, like medium olive Veniard spanflex as it gives a natural colour with the added bonus of making the fly more visible to fish as they emit visible light when exposed to UV light. It's probably also worth mentioning that just because a colour looks really bright, doesn't mean it's actually fluorescent, materials like this will lose colour with depth regardless of how bright they look- not important on the flats but if fishing fishing deep for other species it's worth paying attention to; fluo red will still look red long after non fluo red will have turned purple or black because the red end of the spectrum is the first to be filtered out by the water, while UV at the opposite end of the spectrum has the deepest  water penetration.


Recently though marketing folk at fly tying companies seem to have created a bit of confusion about fluorescent vs UV reflective materials neither of which are new by the way-DFM (daylight fluorescent) wool and floss  were available before I was born and Spirit River was making UV  reflective litebrite in the 80s. The cynic in me says it's deliberate bumf designed to squeeze more cash out of you.  So what's the deal?  Well here's Wikipedia's definition of fluorescence;


Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. The most striking example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the spectrum, and thus invisible to the human eye, while the emitted light is in the visible region.


It absorbs INVISIBLE UV light and emits VISIBLE light.  On the other hand,  UV reflective does exactly what it says on the tin, it reflects INVISIBLE UV light. The only study I've seen on fish ability to see UV light found that juvenile salmonids can but then lose the ability as they mature. So what's the point in paying extra for UV marabou? I think none. Now I'm not saying that a fly tied with it won't work, but I don't think it'll work better, while fluorescent marabou can and often will make a difference. After all, if a fly is easier to see, it's easier to eat. Unfortunately I keep having conversations online or in person with people who buy UV reflective material and complain that they can't see the UV when they put the torch on it, well..... you wouldn't, it's invisible to humans (and apparently adult salmonids). It seems to me the marketers are capitalising on ignorance and charging more for nothing extra. The only exception I've found is with materials, like ice dub or litebrite that are a mix of reflective and translucent fibers. In low light and overcast conditions they also appear, to my eyes at least, more visible than non "UV" versions of the same, especially in the water. Try a comparison next time you're out on a cloudy evening as the sun is going.  Again, if a fish can see it more easily it can eat it more easily. My theory on it is that if the UV is reflected then the visible blue end of the spectrum is also being reflected and then passed back through the translucent fiber which makes it stand out.  Incidentally these are also the same price as the non UV colours of the same product.


As long as you know the difference you can make an informed choice and maybe you believe the UV materials work better and that's fair enough, but until I see some studies showing that fish species I target can see UV light I'll stick with fluorescent!