Blackwood's Edinburgh Magazine — Volume 54, No. 333, July 1843

by Various

We gather from our most recent correspondence with Mr Shaw, (Letter of 8th June 1843,) that he does not regard the range in the spawning period to be followed by a corresponding range in the departure of smolts towards the sea, and in their return from it as grilse. He has found a considerable diversity of time in the assumption of the silvery coating even among individuals of the very same family. "I do not," he observes, "recollect an instance where there were not individuals of each brood reared in my ponds, which assumed the migratory coating several weeks before the brood in general had done so; and these individuals would have migrated accordingly, and reappeared as grilse all the sooner." As the hatching and growth of salmon smolts and other fish, is regulated in a great measure by the temperature of the water in which they dwell, it is very probable that ova deposited late in the season, (say the month of March,) may, in consequence of the great increase of temperature, be hatched much more rapidly than those spawned in mid-winter, and so, by the end of a couple of years, no great difference will exist between them. We remember that, in one of Mr Shaw's earlier experiments, it is stated that he took occasion to convey a few ova in a tumbler within doors, where the temperature ranged from 45° to 47°. They were hatched in thirty-six hours, while such as were left in the stream of the pond, in a temperature of 41°, did not hatch until the termination of seven subsequent days. The whole had been previously one hundred and six days in the water, under a considerably lower temperature.

Mr Shaw has frequently detected individual smolts, both of salmon and sea-trout, (though of the latter more particularly,) descending in some seasons as early as the end of March, and as late as the middle of June, and he has little doubt that some may make their way still earlier to the sea. These, of course, will be found in our tideways as small grilse, weighing one or two pounds, in April and May. The large parr, to which we have already alluded as occasionally met with in rivers, and which we regard as young salmon remaining (and in this forming exceptions to the normal rule) in fresh water throughout their third year, Mr Shaw, whose opinion we requested on the subject, coincides with us in thinking, "would, in all probability, be the first to quit the river after so long a residence there, when the season of migration approached. These, however, are not the only individuals of their kind which leave the river for the sea long before the month of May." A difference in the period of deposition will assuredly cause a difference in the period of hatching, and in this we agree with Mr Scrope; but we think that a late spawning, having the advantage of a higher temperature as the result of a more genial season, will be followed by a more rapid development, and so the difference will not be so great, nor expanded over so many months, as that gentlemen supposes. Finally, the vagrant summer smolts, to which we have before alluded, may consist of that small number of anomalous fry, which we know to assume the migratory dress and instinct soon after the completion of their first year.

Although the excellence of a salmon's condition is derived from the sea, and all its increase of weight is gained there, yet few of these fish remain for any considerable length of time in marine waters. By a wonderful, and to us most beneficial instinct, they are propelled to revisit their ancestral streams, with an increase of size corresponding to the length of their sojourn in the sea. Such as observe their accustomed seasons, (and of these are the great mass of smolts,) return at certain anticipated times. Their periods are known, and their revolutions calculated. Such as migrate at irregular or unobserved intervals, return unexpectedly at different times. Their motions seem eccentric, because their periods have not been ascertained.

But it is obvious that Mr Yarrell's diminutive examples already alluded to, could not have gone down to the sea with the great majority of their kind, during the spring preceding that in which they were captured; because, in that case, having remained a much longer time than usual in salt water, they would have returned as very large grilse instead of extremely small ones.

Mr Scrope informs us that the most plentiful season in the Tweed for grilse, if there has been a flood, is about the time of St Boswell's fair, namely, the 18th of July, at which period they weigh from four to six pounds. Those which don't leave the salt for the fresh water till the end of September and the course of October, sometimes come up from the sea for the first time weighing ten or eleven pounds, or even more.

"Some of them are much larger than small salmon; but by the term grilse I mean young salmon that have only been once to sea. They are easily distinguished from salmon by their countenance, and less plump appearance, and particularly by the diminished size of the part of the body next the tail, which also is more forked than that of the salmon. They remain in fresh water all the autumn and winter, and spawn at the same time with the salmon. They return also to sea in spring with the salmon. It seems worthy of remark, that salmon are oftentimes smaller than moderate-sized grilse; but, although such grilse have been only once to sea, yet the period they have remained there must have exceeded the two short visits made by the small salmon, and hence their superiority of size. When these fish return to the river from their second visit to the sea, they are called salmon, and are greatly altered in their shape and appearance; the body is more full, and the tail less forked, and their countenance assumes a different aspect."—P. 37.

We are glad to observe that in these opinions regarding the growth of grilse and salmon, our author conforms with, and consequently confirms, the ingenious and accurate experimental observations recently completed by Mr Young of Invershin.[^[11]]

Of all those natural causes which counteract the increase of salmon fry, and consequently of grown grilse and adult salmon, Mr Scrope considers that the "furious spates" which so frequently occur in Tweed, are the most destructive. These not only put the channel in motion, but often sweep away the spawning beds entirely. Prior to the improvements in agriculture, and the amelioration of the hill pastures by drainage, the floods were much less sudden, because the morasses and swampy grounds gave out water gradually, and thus the river took longer to rise, and continued fuller for a greater length of time than in these degenerate days, to the increased delight of every acre-less angler.

"But now every hill is scored with little rills which fall into the rivers, which suddenly become rapid torrents and swell the main river, which dashes down to the ocean with tumultuous violence. Amidst the great din you may hear the rattling of the channel stones as they are borne downwards. Banks are torn away; new deeps are hollowed out, and old ones filled up; so that great changes continually take place in the bed of the river either for the better or the worse. When we contemplate these things, we must at once acknowledge the vast importance of Mr Shaw's experiments; for if ponds were constructed upon the Tweed at the general expense, after the model of those made by him, all these evils would be avoided. The fry might be produced in any quantities by artificial impregnation, be preserved, and turned into the great river at the proper period of migration. There might at first be some difficulty in procuring food for them; but this would be easily got over at a very small expense, and with a few adult salmon more fry may be sent to sea annually than the whole produce of the river at present amounts to, after having encountered the sweeping perils I have mentioned."—P. 43.

Our author then proposes that proprietors should call meetings for the purpose, and that parr, hitherto so named, should now, in their capacity of young salmon, be protected by law. He advises all who have an interest in the river, to consider the wisdom of mutual accommodation; the owners of the more seaward banks being dependent on the upper heritors for the protection of the spawning fish and fry, while they, on the other hand, are equally dependent on the former for an honest adherence to the weekly close-time.