Conservation – by Mike Connor

Before one is really able to conserve something, one must have at least an idea of what exactly one is trying to conserve, and how to go about it. With regard to conservation of fish in freshwater, one is obliged to engage in the study of quite a number of things, in order to be able to do this effectively. These things are covered by the term “limnology”. 

Limnology is the study of freshwaters, including lakes, ponds, streams and rivers. The topics involved can be very wide indeed, physical processes as a result of heat, light, water chemistry, transport, and of course biological processes and their effects on the creatures and plants in these habitats. 

Even after one has gone to very considerable trouble, studied, checked, measured, consulted experts, and the available literature. One must still be extremely careful before actually doing some things. Stream and other ecologies are so extremely complex, some interdependencies are simply not known or understood, that even apparently minor changes imposed on them, can have disastrous consequences.

A propos experts, the following little story might be of immense value when appraising some experts;

A frog is drowning in a quicksand. He looks up and sees an owl on the branch of a tree above. The owl is wearing a T-shirt bearing the name of a well known firm of consultants.

“Owl!” cries the frog, “Can you help me? I’m drowning!!”.

“Well, that´s not exactly correct”, replies the owl. ‘You are being sucked down by what we at Mc Doitalls call a quicksand, and you will suffocate, not drown”.

“Well, can you help me?” calls the frog. “It will kill me anyway!!”.

“Yes, we can help, but it will be very expensive”.

“I don’t care about how much it costs”, says the frog, “I’m dying!”.

So the owl flies around the tree two or three times, hoots a little, and then says “My advice to you, frog, is that you should learn to fly”. And presents his invoice.

“How the **** can I learn to fly when I’m drowning, errrr… pardon me, suffocating, in this quicksand?” screams the frog.

“Ah well, we at McDoitalls don’t get involved in the implementation of our recommendations”.

In many cases one may call on past experience in achieving certain goals, and hope that by doing the same or similar things, similar goals may be attained, or at least previous pitfalls be avoided. Unfortunately, there are no guarantees for this. 

Very great care must be taken when interfering with ecological systems, as exactly the opposite of what one is trying to achieve may occur, or other equally unwanted side-effects have very adverse results. Some changes which have already occurred, have had such far and wide reaching consequences, that it is quite impossible to do anything about them. When looking at projects such as stream renaturalisation, introduction of fish, and other animals, one should be aware of whether such actions are even theoretically feasible. Much time, effort and money, may otherwise easily be wasted. 

Conservation, in its simplest form, would be simply to leave things alone. This of course is quite impossible nowadays. There are already so many things which have affected our environment that it is impossible to even list them all, and their various effects.

What many try to do, is to ameliorate some of these effects, even reverse them. Or at least to conserve and improve what is left.

Here again, what one person considers an improvement, may be anathema to another, or of no interest at all. Obtaining the wherewithal, and the necessary consent for improvements, or changes generally, which also invariably involves achieving a majority of votes, even among like-minded individuals, is no easy task.

Once having done so, the implementation of such projects is also fraught with difficulty. I will digress somewhat ( as is my wont!) in order to illustrate this.

Struggling up the bank dragging a large dripping sack, he paused for breath at the top and saw me standing there.

“Morning”, I said. “What exactly are you doing?”.

“Oh I am just getting some gravel for my aquariums. Just the right size this stuff, have to wash the slimy bits out though”. He replied.

Not at all surprised that it was “just the right size” for a host of things, as I had personally barrowed in about a ton of it some six weeks before, after carefully selecting it at a local quarry, along with several other club members. I proceeded to explain to him that he was in the process of destroying a redd, and that the slimy bits floating downstream as a result of his not inconsiderable efforts were fish eggs.

“Oh” he said, apparently unimpressed. “I didn´t know that”. “It´s my last sack anyway”.

I proceeded once again to explain to him, that it was not only his “last sack”, but that the sacks now sitting in the back of his pick-up must be returned to the stream immediately.

He got quite upset at that, “What do you care, it´s not your fucking gravel anyway. I can take what I like from a public stream”.

Tiring somewhat of explaining anything at all, I agreed that it was not my “fucking gravel”, it had been expressly provided by the members of my club, at considerable effort and expense as “fish fucking gravel”, and he was engaged in destroying the excellent and extremely heartening results of such activities, by digging it up, and stealing it, at the same time killing all the fish.

He got even more upset at this. In the meantime, my colleague, who was still waiting somewhat downstream of the whole business, had called the police, and several other club members.

By the time the police arrived, several club members were already there, and had succeeded by means of main force in preventing the gentleman from driving off, and also in preventing him from braining me with a sack of gravel. 

He was screaming and cursing like a lunatic, and generally behaving as if he was unhinged. A few friendly words from the policemen, and being told that he would be charged with a number of very interesting sounding offences if he did not calm down, and start behaving reasonably, eventually shut him up.

We removed the sacks from his pick-up, and tipped the gravel back into the stream as best we could. The redd was pretty well destroyed, but we did our best to cover it up again.

As it turned out, the gentleman owned three pet shops in the area, and had been collecting gravel from a couple of our feeder and breeder streams for several years. He was selling this, packed in plastic bags of 1kg, at a premium price, to people who wanted gravel for their aquariums.

He had slightly over five tons of gravel in the back-yard of his main shop when the police checked, along with a large and varied assortment of stones and boulders. Apparently it was a most lucrative endeavour.

The hefty fine and compensation he was obliged to pay, including the cost of transporting it all back to the streams, hopefully made a big dent in his profits, but somehow I doubt it.

My colleague and I had noticed that a fairly large number of fish, and a few birds, were concentrated at the confluence of the feeder beck with the main river, and after watching the rather frenzied feeding activity for a while, we had waded across the river further down, where this was possible, and then wandered up along the feeder beck to investigate such a relatively unusual occurrence.

The fish were having a field day on the eggs that were being washed down the beck. But for this, we would never have discovered the damaged redd, or ever found out that this fellow was rendering a great deal of effort and expense useless by digging up redds for the gravel. Some of the members had remarked on the fact that redds seemed to disappear sometimes, but had put it down to flooding etc.

Not too long ago, we had a similar case on another stretch. We had managed to acquire Several lorry-loads of medium to large boulders. Natural stone of various types, and had struggled along the river banks with these, sometimes six men to a stone, and using a floatation collar for the very heavy stuff. Placing these at various strategic locations on the river, as fish holding areas.

Imagine our surprise, when some of us went the next weekend, and all the big boulders were gone! We later discovered that another “nature lover” had come down with his sons and a helper or two, and dragged the boulders out, and they were now part of his really quite excellent “rock-garden”.

When we place such stones now, we anchor them to the bottom! There are various ways of doing this, although none is absolutely foolproof, and if somebody is determined enough, he can still get them out. We also mark the stones, in such a way that we can recognise them again, and prove they are ours, if necessary.

There is no way to do this with gravel of course, although a chemical analysis will show where it came from usually. This is not a lot of use in proving a case though, as the gravel may have come from practically anywhere originally.

“Fascinating”, you are probably thinking, “but what has this got to do with conservation? Some greedy little businessman flogging gravel which he has nicked from a stream, is not really a major conservation concern anyway, or is it?”.

Well it is, but probably not for the reasons one might at first imagine. Of course the redd was destroyed, and of course all the work was for nothing, and we doubtless had less fish that year as a result.

But the main reason is, the chap with the gravel, and the chap with the boulders, did not even think they were doing anything wrong!

Stream improvements are all very well, and necessary. Breeding and planting fry, minnows, bullheads, trees, bushes, etc etc. All very excellent endeavours, useful and laudable. 

Unfortunately, they are also a complete waste of time, unless people are aware of the reasons for doing these things, and why they are necessary.

Conservation takes place primarily in the minds of men, not on stream beds. This is where a great deal of our “improvement and conservation work” must be directed.

At least it must if you wish your children, or their children, to be able to enjoy the same things you were able to. Even just a pleasant walk along your local stream.

Such things must be more important to you than having an impressive “rock-garden”, or an aquarium full of tropical fish.

Things which occur elsewhere must also be important to you, not just fish-kills on your local stream. Even though you are unable to do anything much personally about the extermination of whales on the high seas. It should still be important to you. If it is not, then you are not really a conservationist. Not all anglers are conservationists anyway, although most apparently like to think they are.


As we all learned in school, water is H2O. one Oxygen atom and two Hydrogen atoms bound together into a molecule which forms water. This is indeed the case for pure water. However, what we have in our streams, rivers, lakes, and ponds, is much more than that.

Depending on the things dissolved in it, the temperature, and a host of other related factors, the water is affected very considerably in its properties and characteristics. This in turn affects all the animals and plants that live in it.

Some knowledge of water chemistry and related subjects will actually help you to catch more fish. Animals behave in various ways depending on their environment. Fish, as far as they are physically capable of doing so, will always be in the most comfortable or otherwise advantageous zone for them, with regard to temperature, oxygen content, etc and also usually close to their food source. Some fish, like trout, which are territorial, will also have a bolt-hole somewhere close by. 

Oxygen content? Why oxygen content? Water is H2O, there is loads of oxygen in it isn´t there? and fish breathe water anyway don´t they?

The answer is no. Fish breathe oxygen, but they do not extract it from water molecules. They are reliant on dissolved oxygen, free molecules of O2 (oxygen can not normally freely exist as a single atom due to its reactivity, it is only found as molecules), which they extract by means of gills. The amount of oxygen which can be held in solution in water is dependent on the temperature of that water. Cold water can hold more dissolved Oxygen than warm water.

Gills vary quite a lot in structure. For our purposes, at least as far as the fish we mainly catch are concerned, we are most interested in the so called “opercular” gills. These are characteristic of bony fishes, and consist of a single large gill pouch, a single opening to the water, and a mobile “operculum” (gill-plate) covering the opening.

Other important functions are also carried out by Gills,(some of which are not as yet completely researched), the main one being the excretion of nitrogen waste. All animals produce nitrogen compounds as by-products of dietary protein. One such compound is ammonia, which is highly toxic. Many animals, including humans and some fish, convert ammonia to a substance called urea. 

Although less toxic than ammonia, urea must still be excreted. Terrestrial animals do this through urination formation in the kidney. How the elimination takes place in fish, however, is not so well understood. It is thought that they transfer urea across the gills by means of diffusion. 

The gills also contribute to the fish´s osmoregulation. Osmosis is the diffusion of substances through permeable membranes.

The body fluids of a freshwater fish contain more dissolved salts and ions than the surrounding water. As a result of this imbalance there is a constant influx of water into its body and a loss of salts and ions from the blood outwards. 

Consequently the fish has to rid itself of excess inflowing water by constant excretion of a weak urine solution. Fresh-water fish may urinate up to thirty per cent of their body weight in 24 hours. Various salts etc are removed from the urine before it is excreted, and others are actively extracted from the water by the gills in order to maintain the required internal levels. This constant process requires energy, and is essential to the survival of the fish. Anything which affects this process will either damage or kill the fish.

By the way, in marine fish, the situation is reversed! The sea contains more salt and ions than the fish´s body, and so there is a constant movement of water out of the fish into the sea. In order to replace this, marine fish actually drink sea-water and excrete the excess salts etc. Special cells in the gills known as chloride excretory cells are used here.

Obviously, any water changes which affect the fish’s osmoregulatory systems, either fresh water or marine, will invariably prove fatal. In fresh water,fish will rapidly accumulate water, and in the sea, they will dehydrate. 

To recap then. A fish, simply because it lives in water, has to contend with two major problems. Relatively low levels of available oxygen, and the need to constantly regulate and maintain the make-up of its body fluids. 

Various chemical interaction, or physical changes in water can easily and quickly prove fatal to a fish as a result of this.

Here we have an inkling of one reason why some fish have very clearly defined temperature ranges. Fish are cold-blooded. This means that their body temperature is dependent on the temperature of their surroundings. When the temperature starts to rise, oxygen is driven off, and the capability of the fish to extract it from its surroundings no longer suffices. Above a certain temperature, there is simply not enough dissolved oxygen to supply the fish any more, and it will eventually die. One common symptom of trout which are being starved of oxygen, is the fish coming to the surface and swimming around with their jaws open. They are attempting to gain oxygen from the air.

This may often be observed in high summer on still waters, when the water temperature has steadily increased to a point where a great deal of the dissolved oxygen has been driven off, and this is insufficient to support the fish. The temperature itself is not the main problem for the fish, the lack of oxygen caused by the high temperature is. 

Having said that, sudden temperature changes of only a few degrees can have unpredictable and often even fatal results on fish.

Fish are not the only creatures with this problem. Practically all the organisms which live in our waters require oxygen in order to survive, although there are some notable exceptions. Most aquatic creatures use gills in one form or another to extract dissolved oxygen.

Many immature insects use external gills, connected to trachea ( which would be the windpipe in humans). Mayflies for instance may be distinguished from immature damsel flies and stonefly nymphs, by the presence of gills along the abdomen. These look much like feathery leaves, and the trachea may be clearly seen within them. (The term “mayflies” is used here in the international sense, to cover all Ephemeropteras, and not just the large mayfly species E.danica, etc).

Major respiration occurs through the abdominal gills, but some gaseous exchange also occurs through membranes in the body wall. Some species may vibrate their gills in sequence, giving the gills an undulating appearance .This increases the flow of water over the gills and aids respiration.

Oxygen then is of absolute primary importance here. Without it, or with too little of it, many creatures will simply die. Constant oxygen deprivation will also have other deleterious effects. An animal which is unable to breathe properly will not feed very well, and there are a number of other side effects.

Osmotic regulation is at least as important as the oxygen supply.

So, we have discovered that freshwater fish do not drink but urinate a lot, and marine fish drink like fishes, and hardly urinate at all!

Mind you, I hope we have discovered a few other things as well!

Moving on to other aspects of water chemistry and its effects on the plants and animals which live in it, we come to the much quoted and often misunderstood pH value.

pH is defined mathematically as the negative logarithm (base 10) of the H3O+ concentration. PH values are calculated in powers of 10. The hydrogen ion concentration of a solution with a pH of 1.0 is 10 greater than a solution with a pH of 2.0. The greater the hydrogen ion concentration, the smaller the pH; when the pH is above 7, the solution is basic (alkaline), and when it is below 7, the solution is acidic.

I bet you are glad to learn that?

To put it simply, the pH scale is an arbitrary scale by which the acidity or alkalinity of a solution may be determined.

For water containing fish and other creatures this is of paramount importance. The pH scale runs from 0 to 14, with values below 7.0 becoming increasingly more acid, and above 7.0 increasingly more alkaline. As a rule, a neutral pH – 7.0 – is fine for most fish, but they also will do well in moderately alkaline water – closer to 8.0. Some fish can tolerate mild acidity, but few will do well under such conditions.

Fish will not tolerate sudden changes in pH. Although they are able to tolerate values outside their ideal range if slowly acclimatised.

The pH of a water affects the animals in it very considerably. In acidic peaty waters, growth rates are low, the total supportable biomass is much less than in similar streams of a less acid nature. Aquatic insects and plants are fairly rare, and the habitat is generally not really suitable for fish and many other animals and plants. There are fewer species extant, and even small imbalances in such streams will cause major damage to the inhabitants, as they are already living at the limits of their capabilities.

Many upland waters have been affected in recent times by acid rain, and others are also being affected by it. Results of acidification of various freshwaters were first accurately identified in the early 1980’s. The effects are often extremely severe.

Acid rain is caused by the release of sulphur and nitrogen gases into the atmosphere from the burning of fossil fuels, much of which is then converted in the atmosphere to sulphuric and nitric acid. The increased acidity of the resulting rainwater causes much higher concentrations of toxic metals in rivers and streams, notably aluminium, which above certain concentrations, is poisonous to fish and other aquatic life. Not only aquatic life as such is affected. many birds and other animals which feed on or near the stream on various insects and other flora and fauna are severely affected.

Salmonids are especially affected by such changes, as their main habitat, and most especially their spawning grounds, the headwaters of cold clear streams and rivers, are severely damaged by it. Especially young fish are unable to survive such acidic conditions, and the population declines, or is even eradicated.

We are reminded of the unfortunate teacher;

“Alas, the chemistry prof he is no more, for what he thought was H2O, was really H2SO4″

Forestry projects with coniferous trees exacerbate the problem considerably, as such trees scavenge pollutants, and increase the acidity even further.

In some cases, where it is practicable, large scale and constant dosage of lime may be used to buffer such effects, and this has been done in a number of places with some success, it is however very expensive and difficult.

In order to protect and conserve the fish, the habitat itself must be conserved and protected, and this is proving very difficult indeed in many places. There are now such difficulties on a global scale, and no immediate solution in sight.

The final bill for burning fossil fuels on such a massive scale may be a very great deal higher than anybody now imagines, although some are beginning to realise it.

Even if this massive pollution were to cease immediately, which is not likely, it would still take a very long time for many systems to normalise, if they ever did.

I have tried to group these various subjects into orders of importance, but it is not really possible to do this exactly, and so what follows is not in any particular order of precedence.

And so we move merrily on to ammonia, ammonium, nitrite, nitrate, phosphate, sulfide, and various other interesting bits and pieces.

One of the most informative pieces I know of on the nitrogen cycle, is here ;

As it saves me a great deal of typing and research, and is also doubtless of considerably more use than my wittering on, I have taken the liberty of using it here.

On then to other things, among which, water hardness seems a reasonable place to start.

Water Hardness
The degree of water hardness is dependent on the amount of dissolved minerals, especially calcium and magnesium, in the water. It is generally expressed as the amount of calcium carbonate (CaCO3). It is measured in ppm (parts per million), kH (carbonate hardness), and dH (degrees of hardness) or gH (general hardness). Water is described as “soft” (having few dissolved minerals) or “hard” (having many dissolved minerals. General levels of water hardness are expressed in the table below (1 dH is equivalent to about 17 ppm).


very soft 0 to 70 ppm0 to 4 GH (dH)
soft 70 to 135 ppm4 to 8 GH (dH)
medium hard 135 to 200 ppm 8 to 12 GH(dH)
hard 200 to 350 ppm12 to 20 GH (dH)
very hard over 350 ppmover 20 GH (dH)

So what does this tell us about fish?

Well for one thing, it tells us how to set up our gear for electro-fishing!

Passing an electrical current through the water,allows one to measure the level of conductivity. The measure of conductivity indicates the amount of ions (electrically charged particles)present in the water. The harder the water,the greater the conductivity. Measuring conductivity of the water only finds the total amount of ions present in the water, and does not give the origin of the ions, whether they are Mg, Ca, or Fe. 

Water hardness is extremely important as it affects so many areas. The hardness of the water has major effects on pH and pH stability. It also affects the toxicity of many common substances. Also it affects fish osmoregulation very considerably.

So what actually is water hardness?

Water accumulates many dissolved substances on its various cycles. Hardness is really a measurement of the concentration of divalent metal ions such as calcium, magnesium, iron, zinc etc, usually acquired as rainwater percolates through the earths crust, especially certain rocks. Most water is hard because of calcium and magnesium salts, with trace amounts of other metals.

Two types of hardness:

Unfortunately, the subject is somewhat confusing because there are two types of hardness that we need to consider, one is permanent hardness, and the alkalinity (often referred to as carbonate or temporary hardness). The sum of both types of hardness is referred to as general or total hardness.

Alkalinity is the hardness derived primarily from carbonate and bicarbonate ions and directly reflects the buffering capacity of the water. This form of hardness is also called carbonate hardness or temporary hardness because it can be precipitated and removed by boiling the water. This is the lime-scale which forms in kettles.

Permanent hardness is a measure of the other ions present, such as nitrates, sulphates, and chlorides etc, that are not removed by boiling. These are not usually involved in buffering but can affect pH values.

The buffering capacity of water is dependent on the total amount of bicarbonate and carbonate present. Water with low amounts of these ions quickly loses its ability to buffer pH fluctuations.

Carbon Dioxide

Contrary to popular opinion, the carbon dioxide content of streams and other waters is not generated by anglers farting in their waders, and is not directly related to how many pints of fizzy beer one consumed the night before.

It is in fact simply another gas present in water, which is a byproduct of the respiration of the organisms living in it. During photosynthesis, plants require carbon dioxide. If there is insufficient carbon dioxide, the leaves of plants begin to yellow, and growth slows .Some of the carbon dioxide dissolved in water forms carbonic acid, which lowers the pH. If there is too much carbon dioxide the fish and other organisms will suffer. 

That is probably more than sufficient for the time being.

Incidentally, one or two people asked me if it is really necessary for an angler to know all this stuff. Well, it is here, if you want a fishing licence in Germany, you will have to know all this, and a great deal more, as you have to pass a test in order to obtain the licence. many people learn fairly intensively what is necessary for the test, and then promptly forget most of it. Others go on to learn more.

This and other similar articles are based largely on notes which I use for instructing people studying for a licence.

While such information and knowledge may not always help you to directly catch a fish, under any given set of circumstances, it will certainly improve your chances generally, and also give you a lot more insight into the environment in which your quarry lives, and that cant be bad!


There is a very great deal more to be said about water chemistry, and its various effects, but these articles can only really touch relatively broadly on a few things, and an in-depth review of even parts of the subjects covered would require far too much space and time, and a great deal more knowledge and expertise in these fields than I possess. 

I am an enthusiastic amateur, and I indulge in these things as a direct result of my angling hobby. When writing these articles, I make every possible effort to ensure that the information therein contained is as accurate as it can be at the time of writing. My time and resources are of course limited. Like most of you who are reading this, I am most unjustly obliged to waste very large amounts of my time and effort in working for a living. I would much rather be off somewhere fishing, or collecting insects, or tying flies, and engaging in similar important and fascinating endeavours. Alas! such is life.

Should you wish to learn more about these things, and I hope you will, it is all part of being an angler and conservationist, and this is really just a foretaste of some of the fascinating things awaiting to be discovered in the course of your angling career, then you can find a great deal of information on the internet quite easily, by the judicious use of various search machines like Google, and others. Searching on practically any of the obvious keywords in these articles will bring you a wealth of information at the touch of a button.

One or two people asked why I do not give a list of attributions for all these things. There are several reasons for this. I have gleaned much of this information over a considerable period of time, from a wide variety of sources. I could not possibly say where I first heard or read it. This is not a scientific paper, or a commercial publication, and I earn nothing from it, it is designed solely as an introduction to some subjects for interested anglers. 

Giving great long lists of references, which hardly anybody is likely to read anyway, would be a waste of time and space. Lastly, with the advent of the Internet, which you have access to if you are reading this, it is relatively easy to obtain and check information simply by searching on the relevant keywords. 

Chemical indicators were more or less covered in the last article. For many of these, special tests and equipment are required, although some are quite simple, others are quite impossible to carry out without the relevant equipment and knowledge.

Fortunately, there is another more direct, and also rather easier, (at least in its simplest form), way of ascertaining general water quality and conditions. This technique is now used as the preferred method of professional testing in many places, and uses biological indicators.

Indeed, one can even obtain historical data using such indicators, which is not possible with a simple chemical test. If you stick litmus paper in the water, and discover it is acidic, you only know that it is acidic now, not what it was like an hour ago, or a week ago, or even last year. It is also impossible to predict a trend from such a measurement, although a series of measurements over a period of time might allow you to do this. 

Biological indicators can provide such information, one simply needs to be able to interpret them.

“Grooan!!!!!….”, ripples through the ranks! “Not more scientific bull shit!?”.

Not really, ( well perhaps just a little?). 

Biological indicators are not some sort of bionic arms which pop up when one goes around a corner on a push bike. They are simply flora and fauna, which by virtue of their existence and condition, attest to the quality and general state of the waters (or indeed other environments) in which they exist.

Short and long term effects of various chemicals and conditions on some of these biological indicators is known, and by carefully studying the indicators, or even just finding some of them, one can deduce the stream conditions at the present time, and also how they were, for quite a long time beforehand. In some cases decades, or even more. They are called indicators, because they give indications, and not measurements. One may also predict some things with great accuracy.

Anglers usually wish to know what the conditions are at present (although current trends and history are often very important as well) and this is quite easy to do. One simply needs to know which organisms to use as indicators.

“I don´t know the short or long term effects of etc etc whatever, on biological indicators, I don´t even know any biological indicators”, I hear you say.

Well, in point of fact, as a fly-angler you already know quite a lot of them. Quite a few of the insects which trout and other fish eat are commonly used as biological indicators. Indeed, fish themselves are excellent biological indicators. 

Some fish are routinely used as biological effluent testers. Not to put to fine a point on it, if the fish in the effluent sample cocks its clogs, there is still too much shit in the water!

The same basic principle of using canaries in mines. As the birds are more sensitive to gas than humans, if the bird falls off its perch, then get out quick.

A basic premise with regard to many common biological indicators, is that if a certain indicator exists in a certain environment under certain conditions, then that environment must be more or less suitable for its existence! It will also most likely be suitable for similar organisms

Simple eh?

So let us have a look at some actual biological indicators.

The major groups are:

  • Fish 
  • Invertebrates 
  • Periphyton 
  • Macrophytes

These types of biological indicator species are important and unique environmental indicators, because they can give information about the condition of a system. They can also be used to give an early warning of pollution or progressive degradation, or indeed of improvements.

The term “indicator species” although often used, is actually not quite correct (“Now he tells us!!!”).

Indicators are actually really groups or types, which can be used to assess general and specific environmental conditions. The existence or behaviour of one single specimen, or even a few, is not a reliable indication.

If one effluent control fish is used, and it dies, that does not necessarily indicate that the effluent is not clean enough, the fish may have choked on a used tampon or a lump of old toilet paper, or even been poisoned by various long chain polymer tensides, or it may simply have had a heart attack. If however, a hundred fish are used, and they all die, then something is definitely wrong! 

An interesting experiment by the way, if you have an aquarium and a few fish you are sick of looking at. Just place a drop or two of washing up liquid in the tank. The fish will be in a similar condition to Monty-Pythonesque parrots in a remarkably short space of time, only sans perch.

For more information 

One can nevertheless carry out a fairly good quick analysis of a water, by simply choosing a few species, and checking for their existence. Or conversely, if one finds certain species in a given water, one may draw certain pretty exact conclusions from this.

Fish have been used for many years to indicate whether waters are clean or polluted, improving or deteriorating. Fish are absolutely first class indicators of water health for a number of reasons. They are easy to identify even in the field, they are relatively easy to observe or collect, they live in the water for their complete lifespan, they differ very considerably in their reactions and tolerances to various amounts and types of pollution, or other factors, they live for a number of years.

In the meantime, there may be other criteria of importance, in fact there almost certainly are, some of my texts and notes are a little out of date. They are nonetheless still valid as far as I can determine.

Most fish species have relatively long life spans, from two to more than ten years in some instances, and as a consequence, can be used to indicate relatively long-term past, and also current water conditions. 

Fish living in a water automatically integrate the chemical, physical, and biological history of that water. They have a very wide spectrum of tolerance ranges, from extremely sensitive to highly tolerant, and their response to chemical, physical, and biological changes in a water is characteristic and specific.

Now this is doubtless really fascinating, but what does it all mean? 

In simple terms, it means if you find a certain type of fish, or other bio indicator in a water, that water must be good enough to support that fish. The condition of the fish, or bio indicator, how many of them there are, their general condition and state of health, may also be used to draw conclusions as to the further suitability or otherwise of the water to that animal, and by means of extrapolation, other organisms concerned.

Benthic macro invertebrates, (or just “benthos”) is the term used by scientists for aquatic invertebrates which live on the bottom. (benthic = bottom, macro = large, invertebrate = creature having no backbone). These are also excellent bio indicators because they also live in the water for all or most of their lives, they tend to remain in areas conducive to their continued existence, they are relatively easy to collect or survey, they differ widely in their reactions and tolerances to varying volume and types of pollution or other factors, they are relatively easy to identify, most live for at least a year, some longer, they are not very mobile, and like fish, they also integrate general environmental conditions.

“OK OK already, so give me an example of an invertebrate bio indicator”.

A fairly simple example of a good bio indicator in a trout stream is the stonefly. Most stoneflies are excellent typical indicators of clean water (there are exceptions, some stoneflies can tolerate dirty water). If you find plenty of stoneflies in your stream, then you can usually safely say that you have pretty good water quality at least.

Chironomids (non-biting midges,”buzzers” ) on the other hand, are typical indicators of dirty water (in streams and rivers).

Basically, it is as simple as that. If you choose a few “signal” species, with specific characteristics, you can assess a water very accurately as to its condition, potential, and past history. Of course far more complex analyses are possible, and indeed very large scale and complex studies are carried out using bio indicators. 

One must also be aware that a water may vary very widely within itself. It may be possible to find anaerobic conditions in some parts of a stream, where all one will find are midges and tubifex worms. Other stretches or areas will yield other creatures which indicate good oxygenation. 

Some common sense must also be applied. If one only collects or observes particular creatures from particular areas, then they will reflect the conditions pertaining in those areas, and drawing conclusions about the whole water from this would be unsafe, to say the least!

We will save ourselves the trouble of discussing Periphyton and Macrophytes, although I am keenly aware of how much you were looking forward to it, and the depth of disappointment you are now experiencing as a result of my failure to do so, and I will instead direct you to a most excellent resource which will explain to you far more clearly and comprehensively than I can, probably all you will ever need to know about bio indicators.This site is absolutely brilliant. 

Most unfortunate that I only found it after researching and typing the above article, while checking some data. As far as information on bio indicators is concerned, the URL would have sufficed.

Oh well, at least it kept me busy for a few hours, and I was pleased to discover that my data was for the most part correct! 

Just to see how many people are following these articles, and how much they are learning, (not that its any of my business of course, but I am a nosy bugger), I will compile a quiz for the next article, similar to the questions posed in the German angling test. There will be a prize for the person who sends in the first set of correct answers. 

We may announce what the prize is, or we may not. (More or less depends on whether anybody donates one!, or whether I have to tie another set of flies!)

Apart from which, the whole thing depends on whether Paul agrees to do it at all anyway! We will just have to hope that a lonely sojourn around the wilds of New Zealand, on a diet of beans and chilli has fogged his senses at least as much as the windscreen of his van, and he simply says yes without considering the ramifications of it all.

Presumably he does not consider ramifications much anyway, as he would otherwise not be on a lonely sojourn around the …………… with beans and chilli!!! 🙂


About Mike Connor

I had the honourable pleasure to get to know Mike Connor while he lived in Germany close to Hamburg. I visited him several times and learned a lot about fly tying, fly fishing and life in general from this most humble, warm and kind man.

He also gave me a lot of his books and also a very nice creel, which is now hanging on the wall here at Skålestrømmen. I used it over several years until it started falling apart. He gave all these things away as he was moving back to England. I then lost contact with him and even after years of research on his whereabouts, I was not able to find him again. I spoke to several others who knew him and we all tried getting in touch with him, without luck. He sort of “vanished” and I really would like to know what happened to him. Really sad as it was always a pleasure talking to him.

Mike has written numerous articles about traditional techniques and methods. These have been published on various websites before, but can mostly not be found anymore without significant effort and the use of “back in time of the internet” services. Back when we had frequent communication I saved most of what he sent me on my hard drive. That was in those times when was one not “online” permanently and the internet was still steam powered.

I believe that this material needs to be saved from disappearing so I take the freedom to publish it here so interested flyfishermen and outdoor enthusiast can enjoy Mike´s work. I do not claim any copyright on this material of course and do not seek economic gain from keeping these texts alive. I am sure Mike wouldn’t mind.

Have fun reading.

Cheers & tight lines,
Thomas Züllich

P.S. – Please feel free to get in touch via email (thomas@skalestrommen.no) should you know Mike as well.

Leave a Reply