Prince. — Why Do Salmon Ascend from the Sea? 129 



Oxygen, Light, Warmth, etc., Required. 



To an active and vigorous fish such as the salmon, the favorable 

 conditions referred to are essential at all stages. "A desire for 

 freshly aerated water," writes a recent authority, "may stir the 

 salmon to ascend swift down-floating streams, as oxygen is needed 

 for the spawn." But a down-floating stream is not sufficient; 

 shallow, clean, gravelly rapids are necessary, and it is impossible 

 to imagine that the salmon consciously recognizes anything of 

 these necessary conditions. "Salmon do not spawn in deep water 

 anywhere," declared John Mowat, who knew more about the 

 Scottish and East Canadian salmon, as a practical man, than any 

 other unscientific observer, after his experience in early life on the 

 famous Scottish Dee, and for over forty years on the finest of the 

 world's salmon rivers, the peerless Restigouche. "They may nest 

 on high gravel bars and beaches," he added, "and these may be 

 covered with ice in winter."* Indeed, I have myself seen cakes 

 of ice floating down the Restigouche in spring streaked with red 

 layers of salmon eggs, deposited blindly by the parent fish in the 

 preceding fall. Of course, the body of water pouring into the sea 

 out of the mouth of a salmon river, is usually cold and well aerated, 

 for it has hurried down many rapids, bounded over many falls, 

 and swirled round endless eddies, and must carry a maximum 

 quantity of dissolved air, but its coldness increases its power of 

 absorption of air and of oxygen, though there are limits to such 

 absorption. As the temperature rises absorption decreases. 

 Thus one volume of fresh water at 0° F. dissolves 0.049 of oyxgen, 

 i. e., about one-twentieth of its volume; but at 20° F. it absorbs 

 only about two-thirds of that amount, i. e., 0.031 or about one- 

 thirtieth of its volume; 475 litres of water will absorb 32 gms. 

 of oxygen at zero Fahrenheit, but if the water is saturated with 

 dissolved air, about 23 gms. of oxygen will be contained in 23 

 cubic metres of water. Professor T. Clowes, in his evidence 

 before the London Sewage Commission, in England, in 1904 

 (Vol. II, p. 115) said that he had found fish able to live in water 

 of 50% of the maximum aeration; but they could survive in 30%. 

 Professor Roule, as is well known, explains the migration of salmon 



* Chaleur Bay and its Products, by John Mowat, Chatham, N. B., 1888. 



