TROUT AND SALMON, JULY 1960
Sporting trout from unfed fry
By
Frank Sawyer
‘I felt they owed this chance to feed and live to me’
The sight one bright morning about mid-April this year of hundreds of little trout, both wild and hatchery bred, prompted me to write once again on the subject of stocking with unfed fry. For these small fish were eagerly feeding at the edges of two small side-streams on the Avon in Wiltshire, and it was very obvious that all had a chance to live in the places they then occupied.
The little fellows from the hatchery had been out a fortnight and I felt they owed this chance to feed and live, to me. The sight of them with their little bellies bulging with the food they had already taken did in fact, give me a feeling of joy.
The hours I had spent looking after them in the hatchery and then planting them out into places where I then saw them, had not been wasted. I felt also that the wild fish owed me something, too, as in past years much work and planning had gone into the provision of suitable environment for them.
Scars had gone
As I looked at these little trout with their eager movements and fast wagging tails, my thoughts went back through the years. It hardly seemed possible that only five years had passed since the cleaning of these streams and the main river had been completed, for the scars of dragline and bulldozer have been completely hidden. No sign showed of what had then looked like a battlefield for we had been ruthless and drastic in our efforts.
But on that April morning a good flow of clear water travelled along from bank to bank. The clean gravel bed was heaped and holed where scores of spawning trout had been active in January. Bright green growths of young weed were already diverting the current into various channels. Then our aim was to make nurseries, to provide places for large trout to spawn and for the eggs to have a chance to hatch and produce young. I had visualised streams of living water where each year a few unfed fry from the hatchery could be placed with the certain knowledge that they had a good chance to live. Here was absolute proof that we had succeeded.
The two streams I visited that morning are each about a quarter of a mile in length. Both have a water supply from the main river which is supplemented by springs all along their courses. The two converge to rejoin the river where the outlet is at a level about two feet below that of the inlets. This fall in level is sufficient to ensure a very fair flow throughout the full lengths of both streams. Average width of each stream is about eight feet and depth of water varies from six inches to two feet.
I have mentioned the lengths and other dimensions for a purpose. From these two little streams, where the combined length is slightly les than half a mile we have, in the past four years, taken a total of 2,500 trout of yearling size and larger – an average of just over 600 each season since the streams were made suitable for trout production.
Actually one trout of yearling size or larger has been produced on average from every 40 square feet of stream bed. This average has been brought about by natural spawning and by the introduction each year of approximately 4,000 unfed fry from the hatchery.
Though good, the average of 600 trout taken annually from the streams is not a true indication of the numbers which were produced. As I have mentioned, both streams have inlets and an outlet which connect directly with the main river. These are unscreened and fish can at any time, if they so desire, leave the streams at either end. Good numbers of trout in the main river near both the inlets and the outlet is sufficient indication that this does happen, and that a stock in each of these areas of the main river is maintained by production in the streams.
Cost is high
The 600 fish, of which the majority varied in length from 5 in. to 9 in. provided a good stock each year for approximately a mile and a half of the fishing water. This stock adds to and supplements that provided throughout this length of main river in the areas which are suitable.
Few owners, associations or clubs, could afford to stock six miles of fishing with an average of 400 yearlings and two-year-olds to the mile each year, for the cost today of such fish is high when obtained from fish farms. But here we think little of it, indeed this stock from the sidestreams only goes to swell the large number of similar-size fish already in the river. Our average yearly expenditure has been about £100 which has been spent to import between 80,000 and 90,000 eggs, to be laid down and hatched to produce fry.
Fry planted out into streams and the main river has for many years been our only stocking policy. Yet only in very recent years has it been wholly effective. In the past four years, which included the drought year of 1959, the total of sizeable trout fish of 11 inches or over) taken by members has exceeded 6,500.
Serves two purposes
This is good when it is considered that the Avon in Wiltshire is small – that the whole six miles of fishing water does not exceed a total of 26 acres. This in lake form, would be thought very small by some, an area of roughly 350 yards square – just a pond when compared to lakes like Chew Valley or Blagdon.
The little streams about which I have written are but two of several we have throughout the fishery which produce a similar average. These were made, as indeed were the others, by cleaning out drawings and carriers which years ago were part of the irrigation system long since abandoned. In a scheme to improve drainage and fishery these old disused and choked water courses were cleaned and graded by bulldozer and dragline excavator; and each was linked to the main river so it could have a constant supply of water to keep it clean. Each stream now acts as the main drain for a block of meadows and for the springs which enter through its bed. They now serve two very important purposes, to drain the land and to act as nurseries.
Drainage can be effected without having a running stream, but the drains need continual attention year after year to keep them from becoming choked again. By linking them to the river course a sufficient supply of water can be discharged into each so that the continuous flow throughout the courses from one level of the main river at the inlet, to a much lower level at the outlet, ensures that they keep clean without much trouble.
Without a running stream (a stream which continues to run throughout the year) passing through these cleaned out drains, they would have been useless to the fishery. To ensure a reasonable flow the fall in level must not be less than about five feet to the miles from the inlet to the outlet.
Trout can, and do, spawn in water with less flow than this. They occasionally spawn in lakes, too, but often this is not from choice – simply because there are no better places. Eggs may hatch in the slower running water and young live through the alevin stage, but the importance of the running stream comes when the fry are ready to feed.
An essential point
My observations have led me to the conclusion that trout fry must have running water to supply them with food during the first few weeks of their life. Without it there is a heavy mortality. In arranging places for the natural production of trout from unfed fry, this is an essential point to keep in mind. To have ideal conditions for trout fry, streams are best which have a fairly uniform gradient. Though necessary to have flowing water this must not be deep. Little fish – little water; which is another good point to keep in mind. Little in this case meaning small in width and shallow in level.
Trout fry in the very early stages can, and do, live in places where a very strong current is passing through the channel. For though it is impossible for these tiny fish to find feeding positions in the racing water, or on the bed over which it is passing, there are, along each outside, plenty of sheltered pockets they can occupy where the flowing water is baffled and checked by the unevenness of the stream edges. Many of these are eddies where the little fish can poise themselves and face in either direction, and yet be within easy reach of food being carried in the main stream.
The study of trout fry food under natural conditions has not, in my view, had the attention it deserves from those who have carried out researches into the lives of game fish. It is the food supply needed by these little fish, just after they have absorbed their yolk sacs, which to my mind is so interesting. This, through the years since I started fry stocking in 1930, has claimed much of my attention, for I am convinced if trout fry live through the first fortnight of their lives (their feeding lives) the battle is almost won.
The more one studies Nature, the more it is possible to realise that provision, in one way or another, is made for all living things. We have periods throughout the year when there is an abundance of this or of that, periods which coincide with the need for certain things. Big trout have an infinite variety of food, but even so, I feel the good health of these large fish is governed by the appearances of certain insects, crustacean, molluscs or smaller fish at the time most needed. Tiny trout need tiny food, a food of just one particular kind. And this has been made available for them in due season.
Larvae of midges
All I have discovered has led me to the belief that it is the larvae of midges that nature supplies for the first food of trout. It is a supply for the first food of trout. It is a supply which lasts but a short time, just long enough, in fact, to bridge the gap to supply the babies with milk, so to speak, before they can feed on solids. In the South Country streams, the period when this baby food is available is from mid-March until mid-April. Not more than a month, but a month which, like a Mayfly season, may vary a few days either way according to weather conditions.
So when one is thinking of production a trout stock by the introduction of unfed fry, it is this period of latter March to mid-April which should have most consideration. For there is this to be said: If you knew large trout needed a diet of Mayflies to survive, you would not think of putting them into a water in August or September. If minnows were to be the main source of food, then most certainly no introduction of trout would be made at Christmas when the minnows are hibernating.
Maybe the statement I have made about the larvae of midges will be confusing unless it is explained briefly. Midges are grouped under the name Chironomidae and included in this family are over 500 species. These vary considerably in size and in habits. So I would like to make it quite clear that when I write of midges, it is some of the tiniest of the Chironomidae to which I refer.
In pure water
It would be most helpful if the Chironomids were grouped according to their natural habitat. There are some which thrive in damp ground, in bogs or marshes. Others are abundant in stagnant pools. Many more are to be found in ponds and lakes and general stillwaters such as canals. But those in which I have interest are truly aquatic and they can only live in pure, running water.
Like some of the Ephemeroptera these little midges can only thrive in abundance where their food is produced in wholesome and well-aerated conditions. It is my experience that all river insects hatch at a time when conditions are satisfactory for egg-laying. Temperature of water, oxygen content and maybe other factors, play a big part.
Weather and water
To put it briefly, the weather and water conditions must be right so that mating can take place, and so that the eggs when laid will have a fair chance of survival. The true life of all aquatic insects is spent beneath water. They have but a short aerial existence just to complete the life cycle.
The hatching, mating and egg laying time for the midges starts about the middle of April, but it is during the stage just a few weeks prior to this, that the insects in their larval form are attractive to the tiny trout, for then migrations of the larvae take place and it is during these migrations or mass movements, that the creatures are to be seen in mid-water and drifting with the currents.
It is usually about the end of February when I am able to see them in any number, and this coincides with the time when the first algae growths appear on the stones and vegetation on the river bed. And I feel convinced that the tiny larvae feed on this. But this is merely conjecture on my part as I have not had the time to devote to a proper study of them.
Sufficient for me to say that the larvae construct a network of tunnels in the algae which is to be seen as a dark green slime on the stones and plants. So numerous are they that I have seen as many as 50 larvae on a single small leaf of water celery and 100 or more on a stone as large as a man’s fist.
The creatures are tiny, and a microscope or lens of high power is needed to detect them. They are not more than a sixteenth of an inch long and are almost transparent. In shape the larvae are not unlike some of the larger of the Chironomids with a sucker arrangement which enables them to attach themselves at each end. Movement is made by push and pull, looping along in the manner so characteristic of this big family.
A living drift
However, while in the tunnels or feeding on the stones and vegetation, the larvae give no opportunity to trout fry to take them. This opportunity is presented only when there is a mass movement of the creatures from one feeding place to another. These larvae are unable to propel themselves, or steer, in any given direction. But they can lift themselves upwards into the water and can be carried with the stream. The movement of midge larvae has, in the past, been described as a living drift. I cannot phrase it better.
It is indeed a drift of living creatures for while being carried in the currents the larvae make convulsive wriggles and looping movements which keep them from sinking to the bed until ready to do so. The faster the stream, the farther the creatures are carried. The wriggling attracts the eyes of the fry.
Now, in the opening paragraph of my first article, I mentioned seeing the trout fry feeding eagerly at the edges of the streams. It was on those larvae they were feeding. Trout fry do not hunt for their food. They find a place where they can intercept larvae brought to them by the currents. If such a source of supply is absent, they die.
Parent trout, when they spawn, do so with the feeling that the location they have chosen is one which should provide a food for their young. It is for the running stream, the running stream with a pure water supply and a clean gravel bed that they search. They must have a place where there will be a continuous flow, where the conditions are such that they will produce the first crop of algae and where midge larvae will be in abundance.
You may begin to think there is much more in the production of trout from unfed fry than just tipping thousands into a stream and hoping for the best. There is. And only when one studies Nature is it possible to help in any production of her large family. You have to start from the beginning, not just chip in about halfway. The beginning in this case is in the arranging of streams, for without water and a clean bed nothing else can follow.
Perhaps after reading these articles, you may realise a little more of what was behind my story of Land Drainage and Fishery Improvements, which was published earlier this year. Only by good drainage can there be clean running streams which are of a depth suitable for spawning trout and for the production of the young. Trout fry will thrive where not a plant of any kind is growing. I found this when fishing in the high altitude lakes in North Sweden where trout fry were more numerous than in any water I have yet seen. But here the water was pure and crystal clear. It was cold too, but the little trout were quite happy and healthy about the rocky and shingly beds of all the feeder streams. In this cold pure water, running down from the snow caps on the mountains, were millions of midge larvae similar to the species I know so well.
A point proved here is that trout fry food is produced in cold water. Here in the South of England I have found that the best results come in the spring-fed streams, and I stress the importance of doing all possible to take advantage of spring sources. Our streams here are all supplemented by spring supplies which enter through their porous beds.
Sunlight is very important too. No algae to feed midge larvae can be produced in shaded parts of a stream. All overhanging branches should be cut well back and this more especially on the south side.
Greatest enemy
The greatest enemy of trout fry is their own species. Before introducing unfed fry to any stream that is small, all trout of over yearling size should be removed. A difficult proposition I agree, but today we have the electrical apparatus. This, used with the caution so necessary, can be the means of accomplishing this task satisfactorily. No high power is needed and care should be taken that no fish is touched by an electrode. Here we use D.C. when all fish are drawn to the positive and can be taken with a hand net before they make any contact.
As well as our streams, we stock all the shallows of the main river with unfed fry. Here of course it is not possible to free the areas of larger trout. But if care is taken in putting in the little fish just a few at a time, and in the shallow, fast running parts, near the edges, the survival rate is very good.
Clean gravel, pure water and fast currents are the essential things to keep in mind. Then Nature has the chance she deserves.
