Hello all -- I wanted to hear thoughts and comments surrounding the article Dr. Wright posted as well as offer a counter theory which I feel is more impactuful in terms of fish relating to a floating dock.
First, let me clearly define that this is NOT a troll post or anything of that nature. I do, however, have some differing opinions on his theory. However, I would also like to clarify that I do not completely dismiss his theory on the fishes preservation instinct completely. It is my opinion that there are other factors beyond age old preservation which often time places bass under floating docks, and other hard surface cover.
To begin, I would like to expand on the temperature concept. I absolutely agree that the water under a dock, generally, is not noticeably cooler than the surrounding water. Given waters physical properties and what we understand of the physics of the motion of water, as well as the thermodynamics of water it makes complete sense that a small dock covering a miniscule area of water would have only the most negligible effect on water temps. Although I agree that the water itself is not significantly warmer, we do know that sunlight heats water and the intensity of that light is rapidly diminishing as studies present that less than half of the surface intensity is present at only three feet. These figures obviously change depending on the specific water conditions. The more clear the sample water the deeper the penetration will be, and conversely muddy or deeply stained water will be much more capable of stopping the light. Over 25% of surface light is incapable of penetrating even over 1 centimeter!
Focusing on the fact that there is a radiant intensity at three feet (and deeper), we know there is an ability for heat to be recognized. While the water itself may not have a discernible temperature variation, any objects resting within this "radiant zone" will be capable of absorbing the heat. So, I postulate that an object at rest is capable of absorbing heat from the sun at a greater rate than the surrounding moving and highly thermally conductive water, especially if that object is dark colored. Given, the fact that it is surrounded by water does help negate the impact as well as the actual depth of said object noting a very quick reduction of intensity of light in water.
Now having said all of that, do I believe that is the primary reason for fish under cover, no -- but to completely ignore the radiant impact of the sun is a bit dismissive. Obviously, depth change is much more effective and has other benefits and thusly I would suggest if a fish did want to cool down, it would just go to a deeper depth usually. But, I do not think we can completely ignore the thermal impact of sunlight penetrating the surface.
I could be wrong, but that's how I understand it. Now, given that, even I do not believe that is the main reason for fish in shady areas. I do, however, believe there is more to it than just the Raptor Effect. Let us consider vision, not of birds of prey, but of the fish. Fish eyes are very similar, in most cases, to human eyes. Now, let's consider a scenario of varying light intensities in which we should be familiar with, then apply those scenarios to fish.
If you have ever been inside your house, looking out at night you have probably noticed a couple of things. A: It's difficult to see outside when it is bright inside, and dark outside. B: Easy to see when it is dark inside, and a light is on outside. Considering that bass are predatory, largely sight based feeders, it becomes evident they would naturally select a situation where they can more easily see. We know, from our own experience, it is easier to see from a darker location looking into a well lit area.
Expanding the effects of light on vision, we should also consider light blindness. Not as in permanent or even flash blindness where the retinal pigments are bleached out; but rather the scenario where you have sunlight hitting your eye directly, and you are trying to see. I'm doing a poor job of describing the situation - consider the following. You are standing in the sun with no hat, and the sun is hitting you in the face. Naturally you will squint, then probably put a hand up to block the sun from directly hitting your eyes, and eventually probably put on a hat and sunglasses. With each of these additional shading techniques you will note that your ability to see increases. A better example is when you are driving into the sun. You are often "blinded" by the light, and will lower a visor to block the sun.
Now considering most fish can't squint, cover their eyes with a hand (Chernobyl maybe? lol) or wear hats, but have the same impacts on their vision, it stands to reason they are likely to migrate to a location where the intensity of the sun is reduced, aka shade. One of the more significant differences in a fishes eye vs human is the way our pupils work. Most fish have fixed pupil sizes. Whereas a humans eye can reduce the glare of light by decreasing the amount of light passing in by reducing the pupil size a fish usually cannot. Their eyes do adjust to different levels of light, however, it is accomplished utilizing a shift in the relative location of the rods and cones in their eyes. This is a much slower process and depending on the fish may take up to an hour for a major shift to occur.
Certainly, beyond being able to see, we should also consider being able to be seen - but not just from above but from prey. A fish silhouetted in bright open water is much easier to see then one hiding in the shadows both from above and below the surface. I don't think there is any need to develop this any further as we all know bass are ambush predators and are obviously keen at utilizing structure and cover to hide themselves. Everything about a bass is designed for ambushing from cover.
So, in conclusion, I would postulate that a bigger reason for fish staying under the surface cover of a floating dock is related to the fishes sight rather than that of being seen by raptors. I think I have demonstrated multiple positive benefits, related to vision, and considering bass are primarily sight based predators (granted they do utilize all other senses and especially use the lateral line), those benefits would likely be high on their priority list. I absolutly do not feel that this is the only reason a fish relates to cover, rather just one area which in this situation I felt needed to be expounded on.
There is much more discussion to be had surrounding light and water. I did not delve into color spectrum which is visible at different depths or the impact of UV or polarized light. I think all of these play a hugely important role in the life any sight oriented fish.
Lastly, I would like to reiterate that I am not attempting to bash Dr. Wrights article. I found it to be quite interesting and the notion of the Raptor Effect, I think does have some merit. The innate behavior to hide from prey is absolutely a valid and salient fact, it is the level of impact in which I am challenging. I am not a freshwater biologist, so it is possible my theories and conclusions are completely misguided; but I felt inclined to dive a little deeper into this and to at least explore the sight related aspect to fish holding under floating cover.
