Making Sense of Carp Senses?
If we slip below the surface and enter the watery domain of our quarry we find ourselves in a very different and often times alien environment. We discover that sounds travel almost four & a half times faster in water than in air and that different wavelengths of light are absorbed more quickly than others. Our visual range becomes very much dependent on water clarity and the pressure on our bodies increases rapidly as we sink deeper.
The biggest mistake we can make as anglers will be to make assumptions as to how carp relate to their world compared to our own. We might navigate both with similar sensory attributes such as smell, taste, touch and so on but a carp enjoys levels of heightened sensorial stimulation hundreds or perhaps thousands of times better than our own and over many areas of its body. Carp are uniquely adapted to their environment and have evolved some very special capabilities that I will try to explore and understand over a series of articles.
As a ‘former’ scientist (I studied parasitology, comparative physiology and biochemistry) I’m always fascinated by the extraordinary adaptations that different species have evolved to survive. Over the past few years I’ve delved deep into a variety of research papers in an effort to gain a better understanding of the different ways carp experience their world. My goal, of course, is to use this knowledge to discover more efficient ways to catch them.
So let’s look at the various senses I’ll be exploring. Taste, Smell, Touch, Hearing and Vision are the classic 5 common human senses but carp can not only exploit these to orders of magnitude more than us but they can also detect subtle vibrations & pressure changes.
When we humans look out into our world we see things in a range of ‘visible’ colors. We see (unless we suffer color blindness) for example the grass as green, the sky as blue and other objects as yellow, red etc and all with a wide range of hues or shades. This is because our eyes have three color receptors (cones) that are tuned to the Red, Green and Blue (RGB) wavelengths of light they receive. White light is made up of all of these three colors.
Our brain then creates a corresponding color related image built on the mix of information it receives from these three (trichromatic) receptors. In very low light conditions these color receptors are no longer triggered and we rely on receptors (rods) that cannot distinguish color which is why at night we see things only in shades of black & white.
An object that appears red is a result of the Green & Blue wavelengths being absorbed by the object and the remaining red wavelengths being reflected.
Some animal species can see beyond the human ‘visible’ range and into the short wavelength ultra violet range. As a result their world will appear very different to the one we see. It is known that some birds of prey, such as the kestrel, can follow the trails of mice or voles because their urine is visible in the UV spectrum. The example below highlights how humans might see an object with normal (RGB) color vision (Left) versus UV only (middle) and a combination of UV & RGB color (right).
This becomes even more accentuated when we compare how species (bees for example) that only have two color receptors instead of three might see a flower. In this example we see a dramatic difference between Human RGB color vision (left) A bee with Green, Blue and UV (center) and a butterfly with RGB & UV (right). Evolution has given the flower a dramatic ‘target’ like appearance in the UV spectrum to guide the bee or butterfly to the nectar source and its corresponding source of pollen.
In 1896, two German scientists, Köttgen and Abelsdorff, made a curious observation. They measured the absorption properties of visual pigments (the molecules that are involved in absorbing light in the cells of eyes) extracted from the eyes of freshwater fish. What they found was remarkable. The pigments in freshwater fish were found to be ‘red-shifted’ towards longer wavelengths than those of marine fish and land animals. Forty years later a scientist named George Wald found that the pigment molecule in the eyes of freshwater fish contained an additional chemical bond that caused the molecule to preferentially absorb light of longer wavelengths. Wald believed correctly that the red-shift was caused by replacing one vitamin (A1) with a second vitamin (A2) and that this permits freshwater fish to peer further into their murky, red-shifted aquatic environment than those of their saltwater cousins in the blue expanse of deep ocean waters. Even more remarkable was the recent discovery that anadromous fish like salmon have an enzyme that allows them to switch from vitamin A1 to A2 as they enter freshwater. This remarkable adaptation allows salmon to transit from blue oceanic water to the more red shifted freshwater environment.
There is another component of light that has proven to be very important for certain animals. The light that arrives at the earths surface from the sun is made up two components that are transmitted at right angles to one another. The electric (E) field travels in a vertical plane and the magnetic (H) in a horizontal plane. Polarized sunglasses work by eliminating or reducing one of these planes effectively cutting out up to 50% of the light passing through the lens. Some animals such as bees and certain birds can differentiate polarized light for navigation purposes (even when the sun is obscured). It is now known that several fish species including carp can also detect polarized light. There is some evidence that migratory fish like salmon may also use polarized light for navigation but there are other possibilities that may apply more to carp. Underwater experiments show that polarized light may help to enhance the contrast and hence perception of objects. The reflection of light from certain objects such as fish scales can also produce polarized light which may lead to recognition and differentiation of predator and prey species.
So how does this relate to carp and more importantly how we fish for them? Research shows that carp not only have trichromatic (RGB) color vision but that it also extends to UV AND infra red capabilities. When you look at the examples above it becomes clear that a carp will have a very different view of its world than our own. The colors they see will not necessarily look the same as those we humans experience and perhaps more important the reflectivity of an object to UV wavelengths can & will have a dramatic impact on its appearance.
This clearly should give us pause for thought when selecting not only bait colors but any tackle item that we introduce into the carp’s domain. All the thinking to date seems to have only considered bait color based on how WE see it rather than from the carp’s perspective. We might all agree that flouro colored baits standout in contrast to their surroundings. But who is to say that is the same for a ‘dull’ looking bait that we think blends in to the lake bottom? Perhaps it also ‘stands out’ thanks to its appearance in the UV spectrum? And how about that camo colored leader, braided line or even certain brands or colors of monofilament?
We then need to further consider how bait color might change with depth or the influence of water color due to staining or turbidity. Longer wavelengths (red) are absorbed more rapidly than shorter wave lengths in water which is why deeper ocean water appears ‘blue’ in color. In clear water red light is absorbed completely within 20 feet of the surface and in as little as 5 feet in more turbid or stained water.
This absorption results in dramatic changes in the appearance of certain colors as we sink deeper.
This video shot in clear saltwater highlights the changes as the color chart goes from the surface down to 80 feet. It is important to remember that red light is lost even more quickly in freshwater and especially when the water is stained or cloudy.
However there is also evidence that flouro colors that react to UV light retain their color appearance at greater depths than regular colors. This perhaps explains the effectiveness of single flouro hook baits but how about that nice dull lead or camo leader that we think the carp can’t see? In the UV spectrum those same tackle items might actually stand out like a sore thumb!
I have not seen any discussion on the impact of UV vision or how turbidity, staining etc might influence the visual perception of a carp. Any increase in turbidity due to suspended solids or algae etc will dramatically limit the penetration of light and more importantly specific wavelengths.
Another thing to consider is how the light changes during the 24 hour cycle. At sunrise and sunset the sun is low on the horizon and its light must pass through more of the earth’s atmosphere than during the middle of the day. As a result the light takes on a more golden, reddish color. Then just before dawn or after sunset the light has a more ‘blue’ hue. Understanding these factors could be used to determine the best bait color to fish at these times.
As part of my ‘research’ I’ll be posting details of my own findings over the coming months so check back for more updates in the future.
Since writing this back in April I saw a talk by Rob Hughes at Carp in the Park this past June. In addition to being a renowned all round angler Rob is known for his scuba diving exploits and his “Below the Surface” features with well known anglers. Rob raised some further thoughts about the effects of light and how it ‘should and could’ impact our approach to carp fishing.
Copyright Iain Sorrell April 21 2017