Fishing for Trout: Reading the Water – Part 2


by Bryant J. Cochran, Jr.


This is the second installment of the series on reading the stream. As stated in part 1; a rivers current ( flow ) is the trout’s conveyor cafeteria line. A trout sits in its chosen feeding station, waiting for his meal to be delivered, just as we sit at a table in a restaurant waiting for our order to be delivered by a waiter or waitress. You can observe this behavior on any stream where you can sneak up on a high bank, using it as an observation post, wearing polarized sunglasses to see below the waters surface film. You will find the trout at their tables, in or close to the current. In front of or behind an obstruction of the current, or in a basin in the stream bed. These locations provide shelter from the current but allow instant access to the food brought by the current. Trout don’t want to spend a lot of energy holding their place at the dinner table.

Your observations of trout behavior will reveal some important facts. When a trout spots a piece of food coming it tips its pectoral fins and drifts up to the morsel, then it grabs the tid-bit by opening its mouth just wide enough, sucks the food in and closes its mouth. With the food captured the trout shifts its pectoral fins and drifts back to the bottom of the stream. The current will have pushed the trout back from his station but he will not return to the table until he is in the slack current next to the stream bed. The trout is a master of lazy and efficient feeding, there is little or no wasted movement. He has to be this way if he wants to grow big. Trout will not chase down a meal unless they are forced to do so because of a shortage of food supply, or they live in still water like a lake or loch. Occasionally you will see a trout chase food but there will be something special about the morsel that they chase, or it will be a young trout or a freshly released hatchery trout not yet wise in open water feeding. As you observe trout feeding you will notice that their side to side feeding is limited to one foot or less. Even choice morsels are ignored if it will take too much energy to grab it. Of course you will find exceptions, but this will be the normal behavior.

As you begin to learn how to read a stream, pick up on the current flow and find the obstructions and other current breaks. If you are a good student and keep a notebook of your observations and fishing experiences, you will become an above average fisherman. Lefty Kreh has said that ten percent of the fishermen catch ninety percent of the fish and I suspect that this ten percent catch all of the really big trout. So look for the places where a trout could rest with out even wiggling a fin and you will find a trout there.

It is important to fully understand that a trout’s mind will not allow it to hide in fear and feed at the same time. With a brain 5mm in size, he is simply not capable of doing two unrelated things at once. A frightened trout is totally frightened, he runs to his shelter and hides, aware of every thing around him. He is not thinking of hunger or of eating, he is far to busy being scared and he certainly is not going to expose himself to danger. This is why you sometimes have to “rest” a fish you are trying to catch.

Oxygen, the other essential ingredient, is directly related to water temperature. The O2 we are interested in is dissolved oxygen, because this is the oxygen the trout breathes through its gills. Dissolved oxygen (dO2) is measured in parts per million (ppm). Trout require dO2 of 3ppm to survive. When water reaches a temperature of 75 degrees fahrenheit 3ppm is the maximum dO2 the water can hold with out some form of turbulence to enhance gas exchange (oxygenation). At water temperatures above 75 f with no oxygenation of the water the trout will suffocate. The dO2 super saturation water temperature is 32 f.

Water temperature also controls the trout’s metabolism. While very cold water can hold the maximum of dO2 it also slows the trout’s metabolism to the point of suspended animation ( a cryogenic effect ). This is the way it works: from 32 f to 44 f the trout is slowed to the point of needing very little food and he has a over abundance of dO2, up to 30ppm. At 50 f to 55 f the trout’s activity increases and they actively feed for long periods of time and they still have an over abundance of dO2. When the water temperature reaches the 55 f to 65 f range you have the ideal fishing conditions. The trout’s metabolism is in high gear and they feed constantly, dO2 is in the 18 to 12ppm range and there is plenty of food. The food; aquatic insects and their larvae, minnows of all types and crustaceans are prolific and abundant. The fisherman only has to give a proper presentation and he will hook a trout. The great decline starts when the water temperature climbs to 68 f. Brown, Brook and Cutthroat trout start to feel what I call the frying pan effect. Unless there is a lot of turbulence to oxygenate the water, the dO2 falls rapidly to perilously low levels. The trout’s metabolism is racing furiously along and he is burning oxygen as fast as he can adsorb it from the water. As the sun heats the water, he uses the dO2 faster and faster. With out some type of escape valve he will suffocate.

The trout reacts to this danger in several ways. The first reaction is to decrease activity as in “the dog days of summer”. Fish sulk on the bottom and feeding seems to be nonexistent. When and if they feed it will be in the wee hours of the morning when the water is at its coolest. Water takes a long time to release heat and pre-dawn is when it will be at its coolest. The trout’s second reaction is to move to a place where there is more dO2 available. This could be as close as the head of his pool where a riffle provides the turbulence necessary for oxygenation of the water or a considerable distance. If there is a spring feeding the stream, you will find trout stacked up down stream of the plume of colder water. Ground water can be 10 to 15 degrees colder than the stream. A high shady bank can attract many trout also.

So, which is most important to a trout, shelter? food? oxygen? As a biologist I have to go with shelter followed by oxygen, water temperature and food. A trout can survive for a few weeks with out food if necessary, but with no place to hide from danger he won’t be there, even if there is plenty of dO2. As a fisherman I am most interested in the food supply, specifically the ease of a trout’s obtaining it. Let’s face it. If a fish isn’t eating you are not going to catch it. If he is too scared or too stressed by lack of dO2, he is not going to eat, and if Mr. trout isn’t opening his mouth you are just practice casting.

Does it matter that you have seen a big trout lying on the bottom of a deep pool under a bridge during the days if he doesn’t feed there? No it does not! When you see a big trout feeding at the tail of this deep pool in the dusk or dawn hours you have knowledge others would kill for. Now you try to figure out why he feeds there, then you can apply what you have learned to find more big trout. Study the current, see, it is slowest at the tail of the pool where it narrows. Just in front of this trout you spot a wee point jutting into the current. Behind this point is a blown down tree with half the trunk under water. Behind this trout there is a bulge in the water about three inches high. Let’s piece together the puzzle. The current slows because of the narrowing of the pool at the tail, concentrating the food. The wee point pushes the food toward Mr. trout, like a billiards bank shot. The fallen tree gives him a place to hide when we blunder into the water or do some other stupid move. The bulge behind Mr. trout tells of a large stone that breaks the current and pushes some water up-stream making a cushion of calmer water. Just the place Mr. trout can hold his position with little effort, and he won’t get pushed backward much when he rises to feed. This is where he is protected from the current. This is his dinner table, complete with conveyor belt service. Now you are reading the stream, now you can go find an other big Mr. trout, all that is left is a great presentation.

The information learned in parts one and two of this series form the knowledge base necessary to fully comprehend what will follow, which is where to look for trout in any stream. How to spot the most likely ” best seats in the house”. In part three we will serve the “meat and potatoes”, now that you have gotten the salad out of the way. Until then, may the good lord watch over you and keep you from stepping in that deep hole in the stream bed.

Continue on to Part 3 of Reading the Water >>