The Salmon of the Pacific.
THE salmon of the Pacific differ notably as a whole from the single species called salmon (Salmo salar) in the Atlantic. Anatomically the Pacific salmon (Oncorhynchus) differ from the salmon of the Atlantic (Salmo) in the greater number (14 to 20) of developed anal rays (the Atlantic salmon having 10 to 12), in the greater number of branchiostegal rays, 13 to 16, the Atlantic salmon having about 11, and in the usually larger number of pyloric cæca, 65 to 180, the Atlantic salmon having 65. In habits, the distinctions are still more marked. The Atlantic salmon spawns in the small streams and runs in the rivers in the fall for a long distance. In the run, the males become hook-jawed and somewhat distorted and many are attacked by fungus, dying before reaching the sea. But they attempt to reach the sea, and a large percentage of them revive, to spawn again.
The Pacific salmon, Oncorhynchus, have more definite runs. In the process of running, they take no food of any kind. The oil in the body is consumed, the flesh becomes pale, the jaws in the males become much elongated, the front teeth are enlarged, the color is changed and the whole body is greatly distorted. After spawning the fishes drift tail foremost in the stream, and all die within about a week. There is no reason to believe that any individuals of any species of Pacific salmon survive the reproductive act.
All the salmon spawn in cold or cooling water. The eggs are hatched when the water cools to 54°. Freezing kills them but any temperature between 32° and 54° is favorable to their development. Any temperature above 54° causes the egg to develop precociously and the young salmon dies. The temperature of the streams of the north fall earliest to 54°. For this reason, the run is earlier in northern waters than in southern ones in Alaska. All the species spawn in flowing water, the male with its tail scooping out the gravel in which the female deposits the eggs and over which the male casts out the milt.
The Species of Pacific Salmon.
There are five species of salmon in Alaska and neighboring regions. These differ widely in habit and in value, a matter of vital importance to an understanding of the salmon question.