This section is from the book "American Game Fishes", by W. A. Perry. Also available from Amazon: American Game Fishes: Their Habits, Habitat, and Peculiarities; How, When, and Where to Angle for Them.
The Wananishe of the Upper Saguenay River, which were long believed to keep exclusively to fresh water, although they had direct access to the sea, have recently been ascertained to be simply a distinct class of the Sea Salmon, peculiar to its own waters, like all the others, and of precisely the same habits and idiosyncrasies; only the peculiar conformation of the Saguenay region and the extreme depth of the river have hitherto prevented such practical observations as were essential to establish the facts. In places the Saguenay is one thousand feet deep, with an extreme average depth for sixty miles from its mouth, and the Wananishe (iva-na-nish, in the Indian vernacular) are not seen until they reach the riffs of the chute, or Grande Discharge, which constitutes the outlet of Lake St. John. Like other Salmon enjoying the same fluvial condition, they spawn in the tributaries of the lake (in nearly all of which they occur), and pass the winters in the lake itself, where they subsist chiefly upon a species of Whitefish (Corcgonns) called Wutouche, which is replaced by caplin, smelt, or other sub-species of Salmonidce in waters elsewhere. They have a xx marking on their bodies, instead of the usual round spots; but there are Salmon in some of the other Laurentian rivers marked in precisely the same way.
Contrary to early notions, which made these land-locked fish an off-shoot of the Sea Salmon, naturalists now agree that the original habitat of the entire family Salmonidce was in fresh water, and that it is the Sea Salmon which has become erratic-the disturbances of the glacial period having driven them out of their primitive inland possessions. But in obedience to the law of evolution which requires posterity to pass through the same biological changes as their progenitors did, all Salmon must be born and live for a time at least in fresh water; hence we find our Sea Salmon coming into the rivers and spending a large proportion of their time in fresh water, seeking there a change of diet and hygienic treatment against parasites and fungus. The spawning season of the Salmon is in autumn, and when they have fulfilled the requirements of nature they remain in the rivers for a greater or less period, according to the time of their arrival and impregnation, and drop back to the sea again in spring. Usually there is a spring run of Salmon which follow the sand-worms and herring-sile, and other shore food, into the estuaries and up into the rivers, often remaining until the water runs low and becomes too warm for comfort, when they drop back to the sea again. Later on come the Grilse, or Adolescent Salmon, some of them already in full sexual maturity, and after them the mid-summer and autumn runs of old fish.
The bulk of the Salmon run up in autumn for spawning purposes, only the earlier runs being for change of water and diet, and for sanitary purposes, as has already been stated. A flood or a "spate" always starts the fish up-stream, and then the fish take the fly or bait best. A great deal of bosh has been written in all the books of the Salmon, for four centuries past, about Salmon not eating, when ascending to their spawning-grounds, but that theory is now wholly exploded. They not only eat, but eat promiscuously and voraciously of a great variety of food, including young Salwonidce and other salt and fresh water fish-fry, shrimps, prawns, sand-worms, crustaceans, cephalopods, and floating invertebrata. Another impression is, or was, that Salmon could only be taken with fly, whereas they readily take natural minnows, prawns, worms, artificial minnows, spoons, and a dozen other kinds of bait, as has been abundantly tested and proven. Indeed, it would not be difficult to demonstrate that flyfishing is the recent revival of an antique art, and that baits only were at one time used by anglers of low degree. Hence their use becoming unpopular, the impression finally obtained that flies only would tempt a fish. Some of these baits, it may be observed, have been found to take best in spring, others in mid-summer, and others still in autumn. Some take best when the water is clear, and others when it is roiled and discolored; some when the water is thin and low, and others on the surge of a mighty flood. There are no conditions or stages, it would seem, when the Salmon will not accept one or more of the above-named baits at some time or other in the course of twenty-four hours, as observers have ascertained. It is remarkable that this question should have remained open for so many centuries, and that none of the books have set the matter right.
Directly in this connection it may be mentioned that the annelids, or sand-worms, play an important part in influencing the spring movements of Salmon. At that season they swarm in from the ocean to breed on the beach flats, either swimming free like eels, in great masses, or housed in their burrows. Indeed they constitute a most important element in the economy of many kinds of fish not only of nomadic and littoral species, but of those which constantly root for them in their beds, like the Tautog, Haddock, etc. It is manifest that the pulpy bodies of these worms, as well as of much other delicate food which Salmon eat in the early spring, dissolve in their stomachs like glucose or starch. It is digested almost as soon as swallowed, and in the absence of visible sustenance superficial observers have decided that they did not eat at all.
As regards the spring run of Salmon, it would be impossible for them to sustain life for the five months intervening until autumn spawning season unless they fed, while in respect to the late autumn runs they but follow the instinct of all pregnant creatures on the eve of parturition, eating a little here and a little there, fastidious, whimsical, ravenous, and indisposed by turns. It would be inexplicable indeed if Salmon alone, of all creatures, were not required by nature to fortify and strengthen themselves for the supremest act of physical existence. Physiology will easily explain why the distended ovaries, pressing upon the stomach and intestines, will not permit the introduction of food, except in very limited quantities, and Dr. Pancritius, of Germany, has very intelligently described the chemistry of digestion in fishes: so that these subjects are problems no more.