Various
Blackwood's Edinburgh Magazine — Volume 53, No. 331, May, 1843
The following list from Mr Young's note-book, affords a few examples of the rate of growth:—
List of Smolts marked in the River, and recaptured as Grilse on their first ascent from the Sea.
18These two specimens are now preserved in the Museum of the Royal Society of Edinburgh.
We may now proceed to consider the final change,—that of the grilse into the adult salmon. We have just seen that smolts return to the rivers as grilse, (of the weights above noted,) during the summer and autumn of the same season in which they had descended for the first time to the sea. Such as seek the rivers in the earlier part of summer are of small size, because they have sojourned for but a short time in the sea:—such as abide in the sea till autumn, attain of course a larger size. But it appears to be an established, though till now an unknown fact, that with the exception of the early state of parr, in which the growth has been shown to be extremely slow, salmon actually never do grow in fresh water at all, either as grilse or in the adult state. All their growth in these two most important later stages, takes place during their sojourn in the sea. "Not only," says Mr Young, "is this the case, but I have also ascertained that they actually decrease in dimensions after entering the river, and that the higher they ascend the more they deteriorate both in weight and quality. In corroboration of this I may refer to the extensive fisheries of the Duke of Sutherland, where the fish of each station of the same river are kept distinct from those of another station, and where we have had ample proof that salmon habitually decrease in weight in proportion to their time and distance from the sea."18
Mr Young commenced marking grilses, with a view to ascertain that they became salmon, as far back as 1837, and has continued to do so ever since, though never two seasons with the same mark. We shall here record only the results of the two preceding years. In the spring of 1841, he marked a number of spawned grilse soon after the conclusion of the spawning period. Taking his "net and coble," he fished the river for the special purpose, and all the spawned grilse of 4 lb. weight were marked by putting a peculiarly twisted piece of wire through the dorsal fin. They were immediately thrown into the river, and of course disappeared, making their way downwards with other spawned fish towards the sea. "In the course of the next summer we again caught several of those fish which we had thus marked with wire as 4 lb. grilse, grown in the short period of four or five months into beautiful full-formed salmon, ranging from 9 lb. to 14 lb. in weight, the difference still depending on the length of their sojourn in the sea."
In January 1842, he repeated the same process of marking 4 lb. grilse which had spawned, and were therefore about to seek the sea; but, instead of placing the wire in the back fin, he this year fixed it in the upper lobe of the tail, or caudal fin. On their return from the sea, he caught many of these quondam grilse converted into salmon as before. The following lists will serve to illustrate the rate of growth:—
List of Grilse marked after having spawned, and re-captured as Salmon, on their second ascent from the Sea.
20These two specimens, with their wire marks in situ, may now be seen in the Museum of the Royal Society of Edinburgh.
During both these seasons, Mr Young informs us, he caught far more marked grilse returning with the form and attributes of perfect salmon, than are recorded in the preceding lists. "In many specimens the wires had been torn from the fins, either by the action of the nets or other casualties; and, although I could myself recognise distinctly that they were the fish I had marked, I kept no note of them. All those recorded in my lists returned and were captured with the twisted wires complete, the same as the specimens transmitted for your examination."
We agree with Mr Young in thinking that the preceding facts, viewed in connexion with Mr Shaw's prior observations, entitle us to say, that we are now well acquainted with the history and habits of the salmon, and its usual rate of growth from the ovum to the adult state. The young are hatched after a period which admits of considerable range, according to the temperature of the season, or the modifying character of special localities.19 They usually burst the capsule of the egg in 90 to 100 days after deposition, but they still continue for a considerable time beneath the gravel, with the yelk or vitelline portion of the egg adhering to the body; and from this appendage, which Mr Shaw likens to a red currant, they probably derive their sole nourishment for several weeks. But though the lapse of 140 or even 150 days from the period of deposition is frequently required to perfect the form of these little fishes, which even then measure scarcely more than an inch in length, their subsequent growth is still extremely slow; and the silvery aspect of the smolt is seldom assumed till after the expiry of a couple of years. The great mass of these smolts descend to the sea during the months of April and May,—the varying range of the spawning and hatching season carrying with it a somewhat corresponding range in the assumption of the first signal change, and the consequent movement to the sea. They return under the greatly enlarged form of grilse, as already stated, and these grilse spawn that same season in common with the salmon, and then both the one and the other re-descend into the sea in the course of the winter or ensuing spring. They all return again to the rivers sooner or later, in accordance, as we believe, with the time they had previously left it after spawning, early or late. The grilse have now become salmon by the time of their second ascent from the sea; and no further change takes place in their character or attributes, except that such as survive the snares of the fishermen, the wily chambers of the cruives, the angler's gaudy hook, or the poacher's spear, continue to increase in size from year to year. Such, however, is now the perfection of our fisheries, and the facilities for conveying this princely species even from our northern rivers, and the "distant islands of the sea," to the luxurious cities of more populous districts, that we greatly doubt if any salmon ever attains a good old age, or is allowed to die a natural death. We are not possessed of sufficient data from which to judge either of their natural term of life, or of their ultimate increase of size. They are occasionally, though rarely, killed in Britain of the weight of forty and even fifty pounds. In the comparatively unfished rivers of Scandinavia large salmon are much more frequent, although the largest we ever heard of was an English fish which came into the possession of Mr Groves, of Bond Street. It was a female, and weighed eighty-three pounds. In the year 1841, Mr Young marked a few spawned salmon along with his grilse, employing as a distinctive mark copper wire instead of brass. One of these, weighing twelve pounds, was marked on the 4th of March, and was recaptured on returning from the sea on the 10th of July, weighing eighteen pounds. But as we know not whether it made its way to the sea immediately after being marked, we cannot accurately infer the rate of increase. It probably becomes slower every year, after the assumption of the adult state. Why the salmon of one river should greatly exceed the average weight of those of another into which it flows, is a problem which we cannot solve. The fact, for example, of the river Shin flowing from a large lake, with a course of only a few miles, into the Oykel, although it accounts for its being an early river, owing to the receptive depth, and consequently higher temperature of its great nursing mother, Loch Shin, in no way, so far at least as we can see, explains the great size of the Shin fish, which are taken in scores of twenty pounds' weight. They have little or nothing to do with the loch itself, haunting habitually the brawling stream, and spawning in the shallower fords, at some distance up, but still below the great basin;20 and there are no physical peculiarities which in any way distinguish the Shin from many other lake born northern rivers, where salmon do not average half the size.
Leaving the country of the Morer Chatt (the Celtic title of the Earls of Sutherland) we shall now return to the retainer of the "bold Buccleuch." We have already mentioned that Mr Shaw, having so successfully illustrated the early history of salmon, next turned his attention to a cognate subject, that of the sea-trout (Salmo-trutta?) Although no positive observations of any value, anterior to those now before us, had been made upon this species, it is obvious that as soon as his discoveries regarding salmon fry had afforded, as it were, the key to this portion of nature's secrets, it was easy for any one to infer that the old notions regarding the former fish were equally erroneous. Various modifications of these views took place accordingly; but no one ascertained the truth by observation. Mr Shaw was, therefore, entitled to proceed as if the matter were solely in his own hands; and he makes no mention either of the "vain imaginations" of Dr Knox, the more careful compilation of Mr Yarrell, or the still closer, but by no means approximate calculations of Richard Parnell, M.D. In this he has acted wisely, seeing that his own essay professes to be simply a statement of facts, and not an historical exposition of the progress of error.
It would, indeed, have been singular if two species, in many respects so closely allied in their general structure any economy, had been found to differ very materially in any essential point. It now appears, however, that Mr Shaw's original discovery of the slow growth of salmon fry in fresh water, applies equally to sea trout; and, indeed, his observations on the latter are valuable not only in themselves, but as confirmatory of his remarks upon the former species. The same principle has been found to regulate the growth and migrations of both, and Mr Shaw's two contributions thus mutually strengthen and support each other.
The sea trout is well known to anglers as one of the liveliest of all the fishes subject to his lure. Two species are supposed by naturalists to haunt our rivers—Salmo eriox, the bull trout of the Tweed, comparatively rare on the western and northern coasts of Scotland, and Salmo trutta, commonly called the sea or white trout, but, like the other species, also known under a variety of provincial names, somewhat vaguely applied. In its various and progressive stages, it passes under the names of fry, smolt, orange-fin, phinock, herling, whitling, sea-trout, and salmon-trout. It is likewise the "Fordwich trout" of Izaak Walton, described by that poetical old piscator as "rare good meat." As an article of diet it indeed ranks next to the salmon, and is much superior in that respect to its near relation, S. eriox. It is taken in the more seaward pools of our northern rivers, sometimes in several hundreds at a single haul; and vast quantities, after being boiled, and hermetically sealed in tin cases, are extensively consumed both in our home and foreign markets. But, notwithstanding its great commercial value, naturalists have failed to present us with any accurate account of its consecutive history from the ovum to the adult state. This desideratum we are now enabled to supply through Mr Shaw.
On the 1st of November 1839, this ingenious observer perceived a pair of sea-trouts engaged together in depositing their spawn among the gravel of one of the tributaries of the river Nith, and being unprovided at the moment with any apparatus for their capture, he had recourse to his fowling-piece. Watching the moment when they lay parallel to each other, he fired across the heads of the devoted pair, and immediately secured them both, although, as it afterwards appeared, rather by the influence of concussion than the more immediate action of the shot. They were about six inches under water. Having obtained a sufficient supply of the impregnated spawn, he removed it in a bag of wire gauze to his experimental ponds. At this period the temperature of the water was about 47°, but in the course of the winter it ranged a few degrees lower. By the fortieth day the embryo fish were visible to the naked eye, and, on the 14th January, (seventy-five days after deposition,) the fry were excluded from the egg. At this early period, the brood exhibit no perceptible difference from that of the salmon, except that they are somewhat smaller, and of paler hue. In two months they were an inch long, and had then assumed those lateral markings so characteristic of the young of all the known Salmonidæ. They increased in size slowly, measuring only three inches in length by the month of October, at which time they were nine months old. In January 1841, they had increased to three and a half inches, exhibiting a somewhat defective condition during the winter months, in one or more of which, Mr Shaw seems to think, they scarcely grow at all. We need not here go through the entire detail of these experiments.21 In October (twenty-one months) they measured six inches in length, and had lost those lateral bars, or transverse markings, which characterise the general family in their early state. At this period they greatly resembled certain varieties of the common river-trout, and the males had now attained the age of sexual completion, although none of the females had matured the roe. This physiological fact is also observable in the true salmon. In the month of May, three-fourths of the brood (being now upwards of two years old, and seven inches long) assumed the fine clear silvery lustre which characterises the migratory condition, being thus converted into smolts, closely resembling those of salmon in their general aspect, although easily to be distinguished by the orange tips of the pectoral fins, and other characters with which we shall not here afflict our readers.
The natural economy of the sea-trout thus far approximates that of the genuine salmon, but with the following exception. Mr Shaw is of opinion that about one-fourth of each brood never assume the silvery lustre; and, as they are never seen to migrate in a dusky state towards the sea, he infers that a certain portion of the species may be permanent residents in fresh water.22 In this respect, then, they resemble the river-trout, and afford an example of those numerous gradations, both of form and instinct, which compose the harmonious chain of nature's perfect kingdom. In support of this power of adaptation to fresh water possessed by sea-trout, Mr Shaw refers to a statement by the late Dr McCulloch, that these fish had become permanent inhabitants of a loch in the island of Lismore, Argyllshire. Similar facts have been recorded by other naturalists, though, upon the whole, in a somewhat vague and inconclusive manner. We have it in our power to mention a very marked example. When certain springs were conducted, about twenty years ago, from the slopes of the Pentland Hills, near Edinburgh, into that city, which Dr Johnson regarded as by no means abundantly supplied with the "pure element of water," it was necessary to compensate the mill-owners by another supply. Accordingly a valley, (the supposed scene of Allan Ramsay's "Gentle Shepherd,") through which there flowed a small stream, had a great embankment thrown across it. After this operation, of course the waters of the upper portion of the stream speedily rose to a level with the sluices, thus forming a small lake, commonly called the "Compensation Pond." The flow of water now escapes by throwing itself over the outer side of the embankment, which is lofty and precipitous, in the form of a cataract, up which no fish can possibly ascend. Yet in the pond itself we have recently ascertained the existence of sea-trout in a healthy state, although such as we have examined, being young, were of small size. These attributes, however, were all the more important as proving the breeding condition of the parents in a state of prolonged captivity. It is obvious that sea-trout must have made their way (in fulfilment of their natural migratory instinct) into the higher portions of the stream prior to the completion of the obstructing dam; and as none could have ascended since, it follows that the individuals in question (themselves and their descendants) must have lived and bred in fresh water, without access to the sea, for a continuous period of nearly twenty years. This is not only a curious fact in the natural history of the species, but it is one of some importance in an economical point of view. Sea-trout, as an article of diet, are much more valuable than river-trout; and if it can be ascertained that they breed freely, and live healthily, without the necessity of access to the sea, it would then become the duty, as it would doubtless be the desire, of those engaged in the construction of artificial ponds, to stock those receptacles rather with the former than the latter.23
Having narrated the result of Mr Shaw's experiment up to the migratory state of his brood, we shall now refer to the further progress of the species. This, of course, we can only do by turning our attention to the corresponding condition of the fry in their natural places in the river. So far back as the 9th of May 1836, our observer noticed salmon fry descending seawards, and he took occasion to capture a considerable number by admitting them into the salmon cruive. On examination, he found about one-fifth of each shoal to be what he considered sea-trout. Wisely regarding this as a favourable opportunity of ascertaining to what extent they would afterwards "suffer a sea change," he marked all the smolts of that species (about ninety in number) by cutting off the whole of the adipose fin, and three-quarters of the dorsal. At a distance, by the course of the river, of twenty-five miles from the sea, he was not sanguine of recapturing many of these individuals, and in this expectation he was not agreeably surprised by any better success than he expected. However, on the 16th of July, exactly eighty days afterwards, he recaptured as a herling (the next progressive stage) an individual bearing the marks he had inflicted on the young sea-trout in the previous May. It measured twelve inches in length, and weighed ten ounces. As the average weight of the migrating fry is about three and a half ounces, it had thus gained an increase of six and a half ounces in about eighty days' residence in salt water, supposing it to have descended to the sea immediately after its markings were imposed. In this condition of herlings or phinocks, young sea-trout enter many of our rivers in great abundance in the months of July and August.
On the 1st of August 1837—fifteen months after being marked as fry, on its way to the sea—another individual was caught, and recognised by the absence of one fin, and the curtailment of another. This specimen, as well as others, had no doubt returned, and escaped detection as a herling, in 1836; but it was born for greater things, and when captured, as above stated, weighed two pounds and a half. "He may be supposed," says Mr Shaw, "to represent pretty correctly the average size of sea-trout on their second migration from the sea." In this state they usually make their appearance in our rivers, (we refer at present particularly to those of Scotland,) in greatest abundance in the months of May and June. This view of the progress of the species clearly accounts for a fact well known to anglers, that in spring and the commencement of summer, larger sea-trout are caught than in July and August, which would not be the case if they were all fish of the same season. But the former are herlings which have descended, after spawning early, to the sea, and returned with the increase just mentioned; the latter were nothing more than smolts in May, and have only once enjoyed the benefit of sea bathing. They are a year younger than the others.
As herlings (sea-trout in their third year) abounded in the river Nith during the summer of 1834, Mr Shaw marked a great number (524) by cutting off the adipose fin. "During the following summer (1835) I recaptured sixty-eight of the above number as sea-trout, weighing on an average about two and a half pounds. On these I put a second distinct mark, and again returned them to the river, and on the next ensuing summer (1836) I recaptured a portion of them, about one in twenty, averaging a weight of four pounds. I now marked them distinctively for the third time, and once more returned them to the river, also for the third time. On the following season (23d day of August 1837) I recaptured the individual now exhibited, for the fourth time.24 It then weighed six pounds." This is indeed an eventful history, and we question if any Salmo trutta ever before felt himself so often out of his element. However, the individual referred to must undoubtedly be regarded as extremely interesting to the naturalist. It exhibits, at a single glance, the various marks put upon itself and its companions, as they were successively recaptured, from year to year, on their return to the river—viz. 1st, The absence of the adipose fin, (herling of ten or twelve ounces in 1834;) 2dly, One-third part of the dorsal fin removed, (sea-trout of two and a half pounds in 1835;) 3dly, A portion of the anal fin clipt off (large sea-trout of four pounds in 1836). In the 4th and last place, it shows, in its own proper person, as leader of the forlorn hope of 1837, the state in which it was finally captured and killed, of the weight of six pounds. It was then in its sixth year, and, representing the adult condition of this migratory species, we think it renders further investigation unnecessary.
From these and other experiments of a similar nature, which Mr Shaw has been conducting for many years, he has come to the conclusion, that the small fry called "Orange-fins," which are found journeying to the sea with smolts of the true salmon, are the young of sea-trout of the age of two years;—that the same individuals, after nine or ten weeks' sojourn in salt water, ascend the rivers as herlings, weighing ten or twelve ounces and on the approach of autumn pass into our smaller tributaries with a view to the continuance of their kind;—that, having spawned, they re-descend into the sea, where their increase of size (about one and a half pound per annum) is almost totally obtained;—and that they return annually, with an accession of size, for several seasons, to the rivers in which their parents gave them birth. In proof of this last point, Mr Shaw informs us, that of the many hundred sea-trout of different ages which he has marked in various modes, he is not aware that even a single individual has ever found its way into any tributary of the Solway, saving that of the river Nith.