Water depth and the effects on fish





Not many of us are able to fish areas where the depth of the water has a great effect on fish. Most offshore and ocean fishermen learn these effects where as 99% of freshwater fishermen don’t know these effects happen, several factors effect the behavior of fish, air pressures, water temps. Water depths. I would like to focus on some of the key factors in Catfish behavior

Air Pressures:
We all hear the weather man talking about high and low pressure systems, stationary fronts, clippers, and other systems that effect our weather, well most effect our fisheries long before we  feel them. These systems all effect how the fish will react in a given time frame, before, during and after these systems move through. You must remember that the faster a system moves through an area the smaller the effect it has on the water and the fish at depth, example: A fast moving high pressure system will only effect the fish in waters up to about 10 to20 feet. Meaning that the front don’t have the time to exert it’s full effect and add pressure to deep water since it is moving too fast to make this happen. Where as a slow moving high pressure system will effect water depths up to 30 feet of so. After this depth the outside air masses has little effect on the water and fish (explained in later text). A low pressure system will effect fish and water in the same manner just with low pressure meaning the depth will not be effected much past 10 to 15 feet. In summer time a fast moving low is what sparks off the typical afternoon summer thunder storm, this is a prime example of a fast moving front. Some time a high pressure system will spark off a storm and tend to move slower and cause flash flooding. These types of systems should be totally avoided in summer as the lightning and rain associated with these systems are the number one cause of fishing accidents and boating accidents, they come up fast and hard and hit with little warning, being caught out in a system like this is the last place you want to be. The gutsy of the catfishermen will be on the water fishing just hours before this type of system moves through. They also tend to catch the bigger fish. They also have the highest accident rate on the rivers. Now for the fun stuff. Remember the magic number of (33) thirty three. For every 33 feet you go in depth you increase the pressure on an object by one atmosphere, so at 66 feet there is twice the pressure per square inch on an objects surface area as it would be at the surface, now if you do the math if an object is one mile down then there is over one ton per square inch pressure on its surface area. Remember I said that air pressure don’t effect fish in water over 30 or so feet deep, this is why, at 33 feet the water pressure over rides the effect of air pressure. So see this if nothing else, the pressure will only effect your are of water if it’s less than 30 feet deep. Once you reach that magic number of 33 feet you start dealing with a constant factor that is easier to predict, Right? Well when will fish go deep and take the extra pressure verses staying shallow and having less pressure on their body. Here again several factors play the game, heat, water level, O2 content, and many other issues will make a fish go deep. You may think they go and come from these depths to help regulate the pressures, wrong this is where the air bladder comes in, all fish have them and it’s the one thing a fish finder uses to find fish. As the fish goes deeper the more inflated the bladder becomes, thus the need to “burp” a large catfish after bringing it in from deep water. The only factor that I have not explained is air temp and the effects it has on the water. It takes about 96 hours for the sun to warm the surface of a river or lake 5 degrees. Several weeks of 85 degree days will bring the water temp up to the air temps, also a rocky shore line will cause the water to stay warm at night as the heat radiates from the rocks to the water. These areas in early spring and late fall are the prime areas to target. So after all this where do we fish???? find a place that is 33 feet deep and lay a big bait on the bottom there and watch what happens. Read more on this and learn as much as you can, the more you understand the effects of weather and such on fish the easier it is to target the big cats.

Jim, 33 feet is revelant, there are other factors I learned about when reserching this article. like P/H and O2saturation, as well as sediment flow at depth and such, so 31 might be the magic number for some parts of the James and 35 might be it for others. the mean tests are done on pureified water in controled labs so the "other" stuff we see in the river everyday plays a big role in how the fish react. think of the test they did with bass. they put 6 3pound bass in a round tank that was all white inside and had nothing in it. then they added a piece of wood floating, the bass went and got under the wood, they then addd a dark spot on the bottom and side of the tank, 2 of the bass went to the dark area and the others stayed under the wood. so this shows that even in the fish world there are 25% of the fish that are not going to act like the rest in the same circumstances.

the best way to explain it like this, when dealing with water from a foot to about 31 feet, the weather and the moon has a bigger play on the pressures and such, and after you get to 31 feet mark the water is more constant. think of it like a room in your house with out an a/c duct, that room will be colder in winter and warmer in summer till the air and pressure "leaches" into that area, so the longer a front stays in an area the more lickly it will effect fish at a deeper depth, a fast moving front will only effect fish in shallow areas.