SOME PROBLEMS OF SALMON.
WE have reached a curiously interesting stage in the gradual accumulation of knowledge of the habits of salmon. The last three or four years have been occupied with the recording in books and journals of the results of extensive experiments in marking fish and in the examination of their scales, and, speaking generally, those experiments have come to an end. A fresh series will doubtless be entered upon, possibly by fresh investigators ; meanwhile, the results already arrived at are striking enough, especially considering the rapidity with which recent knowledge has been acquired. It is hardly conceivable, as Mr. C. H. Cook (" John Bicker- dyke ") writes in the first number of the Journal of the Salmon and Trout Association, that "within living memory certain members of the Fishery Board for Scotland were seriously urging that the grilse did not grow into a salmon," and that certain naturalists would not acknowledge that the samlet was the salmon in his infancy. The experiments and the chronicling of the results obtained by Lord Blytbswood, Mr. H. W. Johnston, Mr. W. L. Calderwood, Mr. P. D. Malloch, and others have changed all that ; though there still remains plenty of room for fresh experiment, and there are certain problems in the history of the fish which remain at present without an explanation.
What we know of the life-history of the salmon at present may be summed up very briefly, as follows : The spawning takes place in late autumn, in the gravel beds of the river to which the salmon have come up from the sea, and the ova hatch out after a period of from seventy to one hundred and twenty days, according to the temperature of the water. It may be convenient to give the dates of the various changes and stages of growth, noted by Mr. Malloch, of fish whose history he observed on the Tay. Let us suppose that the ova were hatched in March, 1903. The young, or alevins, when they have absorbed the umbilical sac and assumed the true fish shape, collect in shoals and are called fry. The fry by autumn (November, 1903) grow into parr, and are two or three inches long. Mr. Malloch has found that these parr spend the winter under stones, and do not move out to feed till the warmer weather of March or April (1904). He has lifted flat stones in winter, in search of larvm, and has come upon three or four parr together, apparently dazed and sleepy. These parr spend the following summer in feeding and growing, and by the end of autumn, when they again retire to their winter quarters (November, 1904), they are handsome little fish, four or five inches long, with barred silos spotted with black and red. This dress they change the following April (1905), when they are two years old, into the plain silver of the smolt; their tails also become forked instead of rounded. Then a very strange thing happens. As smelts they leave the river for the sea, and for fourteen months or more nothing is seen of them. No one knows where they go or feed, except that it is in the sea ; what is known to happen after the gap of fourteen months or more is that seme of them
return to the same river as grilse, weighing from lb. up- wards (May to December, 1906). That these grilse are the smolts of the previous year has been proved by marking the smolts with silver wire in the back or the adipose fin, and by finding these marks in the returning gril o But early a certain proportion of the smolts return as grilse ; the rent he to the sea for another year or more. Those which retarn
the river as grilse spawn in the following autumn, and thee return to the sea. Many of the fish which spawn die, ma*. dally the males, but there is no definite rule as re eras spawning fish ; indeed, there are very few definite rules whieb can be laid down as to the growth or maturity of the salmon at all. There seem to be no fixed principles as to the dote on which a salmon should return to the river which it left a a smolt. Some of the fish marked by Mr. Malloch as smolts returned to the Tay as spring fish between December, 1906, and June, 1907, weighing between 6 lb. and 13 lb. ; there was another run of fish between July and December, 1907, weigh- ing from 12 lb. to 30 lb. ; the next run, the fourth, ended in May, 1908, and the fish weighed between 13 lb. and 40 lb. ; the fifth run was from May to December, 1908, weighing between 20 lb. and 45 lb. ; and the result of the sixth run, lasting from December, 1908, to December, 1909, has not been made known. Mr. Malloch expected the fish to be few in numbers, and to weigh from 30 lb. to 70 lb. But in each of the first five runs the fish were returning to the river for the first time. What has been established, then, is that the salmon fry hatched in 1903 left the Tay in the spring of 1905, and that some of them returned as three-year-old grilse, while others waited until they were four-, five-, and six-year-old fish before they came up to spawn, and pos sibly to die.
The question occurs at once, How do you know that these fish were returning to the Tay for the first time, and that none of them had spawned P The answer is supplied by the experi- ments begun by Lord Blythswood and Mr. H. W. Johnston, and carried on by Mr. Malloch as managing director of the Tay Salmon Fisheries Company. It was in 1899 that Dr. Hoffbauer discovered that the scales of carp are marked with lines which vary in number according to the age and growth of the fish. Lord Blythswood took up the investigation of salmon scales with the same idea, and it has now been proved that the age of salmon can be told with practical certainty to a few months by counting the lines on a well-marked scale. As smolts, the fish add small rings close together to their scales, and the width between the rings varies according to the rapidity of growth—that is, according to the quantity of avail- able food supply. In winter the lines are packed close together; in summer, particularly a summer spent in the sea, the lines lie much farther apart. Again, when a fish spawns, it loses greatly in weight and bulk, but the scales cannot shrink with the size of the fish ; they get cramped together on a shrunken area of skin, and so their edges become broken and chipped. This leaves a permanent mark on the scale. If the fish survives the operation of spawning and returns to the sea as a kelt, it immediately begins to make up growth again. This growth shows itself in expanded lines on the scale, while the process of spawning leaves a dark and broken ring inside the new rings added by feeding in the sea. But the ways in which these lines are added are not invariable. We have by no means learnt all that is to be known from the reading of scales, and not all the experts agree as to the inferences to be drawn. Mr. Malloch, for instance, calculates that a salmon adds on an average sixteen rings in a year, but others do not agree with him. Mr. Cook, indeed, has counted the lines on the scales photographed by Mr. Malloch, and does not read them in the same way.
It is disappointing to learn that the Fishery Board for Scotland is no longer marking smolts on the Tay. Mr. Malloch, quoted by Mr. H. W. Johnston, writing on this subject in the Journal of the Salmon and Trout Association, states that the searching of the Tay Salmon Fisheries Com- pany's nets involves too much labour, so that an extremely interesting series of experiments is now, apparently, to be dropped. It is to be hoped that something on the same lines may be undertaken in other rivers; for the Tay, of course, in some respects is a river which is a law unto itself. It is a great river which runs through deep lakes, and it may well happen that the fish in such a river as the Dee, for instance, with a shorter course and a lesser volume of water, may vary their habits to suit differing conditions. In any case the problems still to be answered as regards the life-history of the salmon are likely to require continued and co-ordinated research spread over a number of years. Some of the questions which were regarded as open a year or two ago seem now to be finally settled. Salmon do not feed in fresh water, although it is true that they take food into their mouths, and may even chew or swallow morsels, such as shrimps or worms. But other questions seem as far off an answer as ever. Why should what are known as " spring fish " ran up a river in the winter months? It is easy to understand that a fish which needed to spawn in November should seek its breeding grounds in October or September. But why should some fish run up to spawn as late as September, and others pre- cede them by eight months, in January and February What law is a salmon obeying which chooses to spend ten months in fresh water, without food, until it spawns and possibly dies ? Why should it not have remained in the sea, feeding and growing, and presumably enjoying itself ? Again, what becomes of the fish which spawn and survive the operation ? We know that grilse which spawn and descend again to the sea frequently return as clean fish to spawn for the second time. But what happens to the clean fish which spawn and descend to the sea ? Mr. Malloch's experiments as regards the smolts marked in 1905 end, it will be observed, just as this question might have been expected to be answered. Are any of the smolts marked in 1905 now alive, and, if so, where are they, and how many times have they spawned P Perhaps we shall never know. But it is difficult to believe that a clean fish which spawned, say, last autumn, and is now on its way to the sea as a " well-mended " kelt, is going to fulfil no purpose in the scheme of things. It must surely be regaining bulk and weight in order to spawn again ; or, if not, for what reason should so much energy be expended? Does the salmon which has once spawned in a Scotch river return to the sea to begin, perhaps, some fresh cycle of exis- tence as an ocean-going fish ? We cannot say that it is not so ; but that is, probably, the only answer which we can give with any certainty at all. The amount of our ignorance as to the ways of salmon in the sea is as unmeasured as the depth of the sea itself.
Previous page
