No sooner had Mr Young satisfied himself that the produce of a river invariably returned to that river after descending to the sea, than he commenced his operations upon the smolts—­taking up the subject where it was unavoidably left off by Mr Shaw[17].  His long-continued superintendence of the Duke of Sutherland’s fisheries in the north of Scotland, and his peculiar position as residing almost within a few yards of the noted river Shin, afforded advantages of which he was not slow to make assiduous use.  He has now performed numerous and varied experiments, and finds that, notwithstanding the slow growth of parr in fresh water, “such is the influence of the sea as a more enlarged and salubrious sphere of life, that the very smolts which descend into it from the rivers in spring, ascend into the fresh waters in the course of the immediate summer as grilse, varying in size in proportion to the length of their stay in salt water.”

[17] Mr Young has, however, likewise repeated and confirmed Mr Shaw’s earlier experiments regarding the slow growth of salmon fry in fresh water, and the conversion of parr into smolts.  We may add, that Sir William Jardine, a distinguished Ichthyologist and experienced angler, has also corroborated Mr Shaw’s observations.

For example, in the spring of 1837, Mr Young marked a great quantity of descending smolts, by making a perforation in their caudal fins with a small pair of nipping-irons constructed for the purpose, and in the ensuing months of June and July he recaptured a considerable number on their return to the rivers, all in the condition of grilse, and varying from 3lbs. to 8lbs., “according to the time which had elapsed since their first departure from the fresh water, or, in other words, the length of their sojourn in the sea.”  In the spring of 1842, he likewise marked a number of descending smolts, by clipping off what is called the adipose fin upon the back.  In the course of the ensuing June and July, he caught them returning up the river, bearing his peculiar mark, and agreeing with those of 1837 both in respect to size, and the relation which that size bore to the lapse of time.

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.

Period of marking.  | Period of recapture. | Weight when retaken.
---------------------+----------------------+---------------

-------
1842.  April and May. |    1842.  June 28.    |     4   lb.
...     ...        |          July 15.    |     5   lb
...     ...        |           ... 15.    |     5   lb.
...     ...        |           ... 25.    |     7   lb.[18]
...     ...        |           ... 25.    |     5   lb.
...     ...        |           ... 30.    |   3-1/2 lb.[18]

We may now proceed to consider the final change,—­that of the grilse into the adult salmon.  We have