A Critical Examination of the Evidence for Physical and Chemical Influences on Fish Migration

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Abstract
It was because of a series of records prepared in connection with a study of the salt-water minnows that so successfully cope with the salt-marsh mosquitoes of the north (Chidester,. 1916) that the writer was invited in 1919 by the U.S. Commissioner of Fisheries, Dr H. M. Smith, to engage in an attempt at the physics and chemistry of the migrations of fish.The subject is one that several experienced zoologists have refused to follow for any length of time, as it is difficult of field observation, and certainly not one to be solved by laboratory experiments.After several summers of spare time spent in experimental work, amplified by field observations, it has been deemed advisable to survey the literature, and this paper will, it is hoped, aid in crystallising our knowledge of the migrations of anadromous fishes.To a zoologist who is looking for a problem that will eventually have a solution, it is most disconcerting to discover that there is much evidence that fish like the salmon are able to return in an apparently inexplicable manner to the streams where they were bred.We are deeply indebted to Dr C. H. Gilbert of Stanford University for most careful work on fish scales that has shown that salmon return to the river of their nativity for spawning, and that they are even able to locate in that river the spot where they were once fingerlings.Jordan mentions certain observations of Dr Gilbert on the Chinook salmon and Red salmon of the streams near Walla Walla, Washington. Dr Gilbert found that at a point where the salmon have a choice of two streams that come together under a bridge, the Chinooks (king salmon) go up either one of the streams indiscriminately, but the Red salmon (bluebacks) turn always to the stream with a lake.In a recent paper Dr E. E. Prince, Dominion Commissioner of Fisheries, Ottawa, Canada, states (1916) that his previous report—published in 1896 and repeated in 1912—to the effect that “each river has its own race of salmon,” is borne out by more recent observations. A dark-fleshed race of Sockeye salmon inhabit a small creek near the Skeena River, and the salmon canners rarely net them as the meat is of a “dark, repulsive colour,” although the distance is not great from the waters that furnish the attractive pink salmon of the regular catch.Dr David Starr Jordan is inclined to question whether migration up the parent streams may not be due to the fact that the young fish do not travel far from the mouths of the rivers that gave them birth, and consequently they find the parent waters pouring into the ocean and quite naturally return to them. Jordan also believes that the salmon are not unfailingly true to their native rivers.Jordan has pointed out the fact that salmon do not apparently care about the quality of the water, and that while the Chilcoot River comes from a glacier and the water is milk white with glacial debris, the fish migrate into it. Jordan (1920) also cites a case of apparent attractiveness of lake water.The first lake on the Yukon River, Lake Labarge, is 1800 miles from the mouth of the river. At Boca de Quadra, also a noted salmon stream, is a little stream about ten feet wide and less than a mile long, the outlet of a lake. At the head of the lake it is fed by clear springs. The fish go up the small stream just as they go up the Yukon, although they have only about five miles to go. Their start is accordingly a late one. Jordan does not explain this condition.Further interest in lake-fed streams is aroused when we cite the case (mentioned by Jordan) of observations by J. P. Babcock of the British Columbia Fish Commission (Jordan, 1919). Babcock observed that in the case of water piped from a lake-fed stream across to another stream, the Red salmon gathered around the mouth of the pipe which contained the lake water.The writer cannot refrain from remarking at this juncture that a fish responds to currents of water, and that it is quite likely that the Red salmon would have gathered around almost any non-poisonous fluid of the optimum temperature, providing it came with a little force through a tube.Our knowledge of salmon behaviour has been clearly stated by Dr C. H. Gilbert in a personal letter, in which he answers several questions asked by the writer, and with his permission the answers will be quoted.“Dear Sir,—I have no knowledge concerning possible factors governing migrations of fishes, and am thus unable to prepare any discussion of the subject that you may care to use. As regards migration of the salmon, however, there are certain unquestioned facts that must be taken adequately into account by any theory which claims to explain their movements.“1. Salmon which are schooling together in the sea on feeding grounds far removed from their final spawning districts, will at the proper time separate and go their own way rather directly to the mouth of the distant stream from which they originated. At the time they separate, it would seem they must assuredly be exposed to identical environmental conditions.“2. Salmon ascending a river together will react differently on approaching a given tributary, though again it would seem they must be exposed to the same conditions. There is a fair body of evidence to show that in the main they will re-enter the tributary in which they were hatched.“3. In both the above instances, we seem wholly at a loss to suggest any purely external factors which condition and guide the migration, and yet lead to such diverse results when applied to fish of different early history.“4. The ‘parent-stream theory,’ in so far as it has validity, is not a theory in any sense of the term, but a bald statement of fact. The salmon either do, or they do not, return in the main to their parent stream at maturity. We hold that they do, but we are far from claiming that this phrase, which is merely descriptive of their conduct, affords any...