Naked Science Forum
Life Sciences => Marine Science => Topic started by: Neil Stephenson on 10/12/2009 19:30:03
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Neil Stephenson asked the Naked Scientists:
Does an Atlantic Salmon see fluorescent colours clearer that no-fluorescent but flashy colours (silver, gold etc)?
What do you think?
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"Eight hatchery-reared Atlantic salmon Salmo salar post-smolts, implanted with acoustic depth sensing transmitters and manually tracked for 5-12 h in the Hardangerfjord (Norway), spent most of their time (49-99%) at 1-3 m depth during the day, whereas four of seven fish tracked were found close (<0.5 m) to the surface at night, with a strong negative cross-correlation between general swimming depth and surface light intensity. Hence, the actual swimming depth of post-smolts during their early marine migration may depend on the light conditions, although the individual variation in vertical movement pattern was large. No cross-correlations were found between light intensity and swimming depth during daytime periods with rapid changes in light intensity, indicating that other factors than light intensity were important in initiating the irregular dives that were recorded down to 6.5 m depth."
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"60 individuals were captured, tagged with acoustic transmitters (of which 20 with depth sensors) and released in the River Alta, Northern Norway. In addition, 172 kelts were also tagged with external Carlin tags to obtain reliable recapture rates in the fisheries. Nearly all (95%) kelts tagged with acoustic transmitters were recorded during their outward migration at four transects of acoustic receivers deployed across the river mouth and Alta Fjord. Most of the kelts migrated through the 30 km long fjord in only 1–2 days (mean time 33 h, range 7–138 h) and generally stayed close to the surface during the fjord migration (individual mean depth of 2 m, range of individual means 0–15 m)."
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I know it should to be absolutely obvious that a fly has to be seen by the fish before there is any chance of catching it but its surprising how often in highly coloured water anglers choose flies that are too inconspicuous. Sediment that stains the river reduces the amount of light and also, due to filtration changes the appearance of colours. Generally speaking yellow and orange are most visible in these conditions. Fluorescent colours I think are particularly useful. Too often I have witnessed greater success by anglers using flies incorporating fluorescent yellow or orange and I am convinced that it makes a substantial difference to your chances. Concealed by the high, coloured water, fish prefer to take the easy routes upstream, avoiding powerful flows they travel close to the banks sometimes in comparatively shallow water. Water between two and four foot deep is often favoured and smooth glides, pool tails or popply water adjoining streams offer prime fishing opportunities. Often fish will be found where you might stand in low water conditions."
"Silver works well under virtually all lighting conditions, but color seems to make little difference on calm clear water. Salmon have very keen eyes. The extreme extent of this was witnessed by me in the late 1980's on South West Brook when I seen a grilse jump from a deep lay in rippled water, in the dark, and grab a black gnat wet fly (an all black fly) in the air! I have never doubted the atlantic salmons eagle eyesight since."
So yes and no :)
They seem to see them and in murky rivers that's what may catch their interest but they seem to swim so near the surface that in clear waters I don't know?
But if you're fishing for the best tips on fishing :)
Fluorescent I guess, I mean hey, they looks nice in the disco too ::))
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And what better way to make a female realize that she found her hunter than a fluorescent wet fly strategically draped over ones body?