Page:Popular Science Monthly Volume 61.djvu/213

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the parent fishes spawned—the 5,000 mentioned in the experiment were from eggs taken in California—but because their ocean feeding grounds are not far off-shore, and in their two years' residence in the ocean they have not wandered far from the point at which they entered it. When it comes time to return to fresh water, their native stream is the first to attract attention.

Adult salmon may be found in the Sacramento River at any time of year. There are, however, two distinct runs, the earlier of which passes up the river during April, May and June, and the later during August and September. The former is known as the spring run and the latter as the fall run. The salmon of the spring run ascend the river to the headwaters, such as the upper Sacramento, McCloud River and Hat Creek, and some of the earlier ones even pass Pit River Falls and enter Fall River. The salmon of this run spawn mainly in August. The fall salmon do not ascend the river so far as those of the spring run, but turn aside into the lower tributaries, or spawn in the main river. They reach their spawning grounds during the latter half of October, November, and the first half of December. The main river is very low at this time of year and only a small portion enter the tributaries.


Details of Migration.

When the salmon enter the bay from the ocean, they come in against the ebb-tide. They stem the current till the tide changes, and then run out against the flood-tide, losing much of the distance gained during the ebb. That they do not lose altogether as much as they gain may be understood from the following explanation:

PSM V61 D213 Salmon progress against the ebb and flood tide.png

The tide runs up the bay and river as a broad low wave, on the upper side of which is flood-tide, and on the lower side ebb-tide. This wave is about three hours going from San Francisco to Benicia; it reaches Collinsville in about four hours, and Rio Vista in four and a half hours. When the crest of a wave is at Isleton, its trough is about at the Golden Gate. The farther the tide extends up stream, the smaller the wave, the shorter the flood, and (as the flood and ebb must together equal' twelve hours) the longer the ebb. The following diagram will illustrate the movements of a salmon in passing through the bays: a, b and c represent the tide-wave at successive points as it passes up the bay. <-< indicates ebb-tide, and >-> flood-tide. Suppose that a salmon enters the Golden Gate, G G, at the beginning of ebb-tide,