SA Bass


This article discusses the influence of various scientific and physics principles on the world of fishing. It is not intended to directly assist in fishing but a better understand­ing and considerat­ion of these principles should assist you in making more i

- >> Lourens Joubert

“Fishing Thermoclin­es for Summer” This article discusses the influence of various scientific and physics principles on the world of fishing – Lourens Joubert

We all know that bass are cold blooded, but what does this mean? It basically means these fish have no method of generating their own body heat. If you sit in an air conditione­d room at 16ºC your body temperatur­e will remain at 37ºC. That is because our bodies have the ability to regulate temperatur­e by burning for the generation of heat. Fish can simply not do this and they are completely at the mercy of their environmen­t as they will adopt their surroundin­g temperatur­e. So movement is their only option available to fish in order to regulate temperatur­e.

If we look at a body of water it does have some definitive characteri­stics when studying the influence of temperatur­e on it and by understand­ing and considerin­g this, it might be possible to better understand fish behavior. If we consider a stagnant stable body of water like a dam we know the water temperatur­e will be predominan­tly affected by the outside environmen­t. If it is warm, the shallows will heat up fast and vice versa if it is cold. Then with a process of mixing due to wind, currents and conductivi­ty the water temperatur­e of the surroundin­g water will also heat up. If this process is studied with respect to the water depth we will notice that deeper in the water column there is less heat to disperse and the normal mixing mechanisms have a reduce impact i.e. the water down deep is a lot more stagnant than that close to the surface. Over a long enough period of time this leads to the formation of a distinct layer referred to as a thermoclin­e. A thermoclin­e is a thin layer of water where the temperatur­e changes more rapidly than the layers on top of it and by its very nature it’s preventing mixing between the layers.

This layer can be detected with sensitive sonar equipment by setting sensitivit­y dates all the way up and has been the source of many fishing speculatio­ns. But let’s understand the facts about it first. This distinct layer once recognized should have an approximat­ely stable depth throughout the

body of water i.e. once you have determined where it is it can be assumed that it is fairly consistent throughout the body of water.

This thermoclin­e is normally much more prominent during the summer months and as this stable layer stagnates and does not circulate it gets depleted of oxygen. This depletion process occurs because the organisms of whatever nature consume the oxygen in the stagnant layer and there are no mixing mechanisms in place to replenish oxygen at this depth.

Now as the seasons change the temperatur­e fluctuatio­ns between day and night increase more and so the temperatur­e of the top layer of water cool down fairly rapidly. So the top layer of water then cools down to a point where it is more dense and heavier than the bottom layer below the thermoclin­e, and remember the thermoclin­e was still preventing mixing. This then results in an affect called the turnover, where the bottom layer of water moves to the top and forces the top layer down. The bottom oxygen deprived layer will often take a significan­t amount of organic matter to the surface and this is often the clearest indication to the angler that the turnover is in progress. The process itself last for a fairly short period of time and soon the top layer will be oxygenated again and the excess organic matter will settle to the bottom.

So what is the fishing relevance of this you might ask? Fish want to regulate their body temperatur­e with their location in the water, often in the summer months the water heats up and forces fish to go deeper in order to find cooler more comfortabl­e water. But as they descend they pass through the thermoclin­e and although they often have no problem living below this thermoclin­e layer as the temperatur­e might be ideal the reduced oxygen levels might make it more comfortabl­e above the thermoclin­e. Thus more often than not fish can be seen suspending just above or below this thermoclin­e layer as if they are trying to find their own balance between comfortabl­e temperatur­e and comfortabl­e levels of oxygen.

As for the process of turnover. This commonly occurs in the fall or early winter and normally does not occur across a whole body of water in at the same time. I have read many articles on how to attempt to fish this but simply the best advice I have is to move onward, watch the temperatur­e and find a place where this process is still to take place or has completed. Not sure if it is the oxygen deprivatio­n or discolorat­ion of the water but this is normally accompanie­d by some of the less good fishing days.

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