Page:Popular Science Monthly Volume 60.djvu/512

504 salmon, gave Miescher peculiar opportunities for this investigation. The salmon spawn during the latter half of November and the early part of December, or just before the shallows of the lakes and streams, where the eggs are deposited, are frozen over. These eggs are hatched by the warmth of the next spring. During the following year the young salmon live in the lakes and streams, and when a year old and from seven to nine centimeters in length swim down the river and out to sea. These facts were easily established. To determine the probable period of the salmons' return to fresh water was more difficult. By measurements of more than two thousand of the fish caught at Basel, together with statistics of those taken in the lower reaches of the Rhine and in other rivers of Germany and Sweden, Miescher found that the greater number both of males and females could be classed under one or other of three sizes. Contrary to what might have been expected the most numerous of these classes is that of the largest and oldest fish, while the least numerous is that of the small 'St. Jacobs' salmon. Unless it be supposed that some of the younger fish go to other rivers, which is unlikely, it is evident that not all the salmon of the proper age participate in every migration to fresh water. These considerations and others, based on the probable rate of growth of the fish, led to the conclusion that from two to three years after entering the ocean, many of the males and a few of the females make their first journey up the river to spawn. This accomplished, the fish return to salt water for another period of about three years. Then occurs a second migration to fresh water by a large proportion of both sexes. The males of this migration average seventy centimeters in length, the females seventy-six centimeters. Probably all of the salmon that have survived the dangers of marine life unite in the third migration. The average males of this age have attained a length of eighty-two centimeters, the females ninety centimeters. These differences in size Miescher regarded as the result of another period of life and growth in the ocean, between the second and third migrations, of at least two years. As only a few salmon of ninety-eight to a hundred centimeters length are taken, and these are all males, it is probable that the females as a rule make only two journeys to the spawning grounds during their lives, while the males ascend the river three or even four times. Within considerable limits of error the probable age of the largest salmon taken in the Rhine is therefore fourteen years.

By a careful comparison of the statistics of the number of the salmon taken in Holland and at Basel, Miescher found that any marked increase in the catch in the lower reaches of the river was regularly followed, after an interval of eight or nine weeks, by the appearance of an unusually large number of the fish in Switzerland. Basel is five hundred miles from the mouth of the Rhine, and if the average current