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Page:Popular Science Monthly Volume 18.djvu/225

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able are the schools of fish of the salmon family that resort to the great rivers of Siberia after the breaking up of the ice.

The resort of the fish to the same place is repeated every year with a wonderful regularity. The appearance of the herring in Norway varies at most not more than fourteen days. The energy of the movements, is remarkable. The salmon, traveling from the sea to its spawning-places, surmounts considerable difficulties, leaping up to the tops of falls several feet high, and repeating its jumps if it fails at first, till it succeeds. Eels are able to ascend waterfalls forty or fifty feet high, and it has been asserted that they have been known to climb the falls of the Rhine at Schaffhausen; and since the sluices have been put down they have been able to pass the six falls of the Trollhätta, which have together a height of a hundred feet.

Fish travel to very considerable distances in these journeys. Brehm estimates that the salmon of the Obi and Irtish travel about 7,000 kilometres (4,340 miles) a year up and down the stream; and salmon and sturgeon often go from 1,500 to 2,400 kilometres (930 to 1,500 miles) from the sea to their spawning-places, and salmon to a height of 2,000 feet above the level of the sea. Salmon may occupy six or eight months in going up the stream and accomplishing their spawning, but will return to the sea in one or two months, traveling from ten to thirty kilometres (614 to 1834 miles) a day.

Fish, like birds, return from the most distant journeys to the places of their nativity. This has been ascertained by marking individuals and watching for their return. This faculty of localization bespeaks a higher degree of intelligence than we have been accustomed to ascribe to fish.

The theories that have been proposed to account for these migrations have failed to give a fully satisfactory explanation of them. The migrations as a whole may be considered under five heads, of which the first and most important comprises the journeys to the places of spawning. The most notable instances of such excursions are those of the salmon tribe, and of the sturgeon, lampreys, eels, and tunnies. The proper home of all these fish, except the eel, is the sea; and, besides the eel, all of them except the tunny make yearly considerable journeys up the rivers to find places suited to the development of their spawn. Such places are, for the sturgeons, about the middle of the course of the river, in shallow, sandy spots; for the salmon kind, among the hills near the sources, or in the fountain-streams themselves, where the water runs in a lively current over a stony or gravelly bed. The lampreys ascend about as far as the sturgeons. Their young, which are very different in appearance from the parents, may be found in great numbers in nearly all the still brooks and ditches of the middle parts of the river-courses. The eel is the only European fish which goes from fresh water to the sea to spawn. Its journeys take place some time before the fish are ready to spawn, an abode in