Note (return) — NATURAL HISTORY OF SALMON AND SEA-TROUT.

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."19