122 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
pass Pit River Falls and ascend Fall River to its source. They are not found in Pit 
River above the mouth of Fall River. By the time they reach this portion of the 
stream, the Upper Pit River is very low and the water impure, and the salmon all 
turn into Fall River. The salmon of this, the spring run, spawn mainly in August. 
The fall salmon do not ascend the river as far as the spring run, but turn 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, 
and spawn soon after. The main river is very low at that time of the year, and the 
portion between Tehama and Redding is an important spawning-ground. (See chart 
of spawning-grounds, plate 17.) 
As a matter of fact there is no definite distinction between the spring and fall 
runs; that is, there is no time during the summer when there are no salmon running. 
First there are a few very early salmon that begin running up the river in February, 
and the number increases until May when it decreases till July; then it increases 
till the first of September when it again decreases, there being a very few each month 
until the next spring run. 
The spawning seasons merge in the same way. The earliest salmon go farthest 
upstream, and as the season advances they stop at lower points. The localities and 
dates of the spawning of the earlier salmon have not been determined, except that 
Superintendent Lambson, of Baird, reports having seen a pair of spawning salmon in 
the McCloud at the hatchery on the 20th of Api’il, 1902, which is the earliest record 
known. By the 1st of October spawning fishes are found as far downstream as 
Redding, and as far as Tehama by the first of November. 
Details of migration . — When the salmon enter San Francisco Bay they come in 
against the ebb tide, stem the current till the tide changes, and then run out against 
the flood tide, losing much of the distance gained during the ebb. How it is that 
they do not lose altogether as much as they gain will be understood f rom the following 
explanation: 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. When the crest of a wave — 
that is, slack high water — is at Isleton, the trough, or slack low water, is about at the 
Golden Gate. This wave is about three hours reaching Benicia and four in reaching 
Collinsville. The farther up the bay and river it reaches the smaller the wave 
becomes, the shorter the flood, and (as the flood and ebb combined must equal 12 
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, GG, at the beginning of ebb tide, which would be 
the most favorable time. His position on the wave wiil be at .s. If he is able to 
travel up the bay as fast as the wave he will keep his position near the crest, that is 
at s. But he can hardly do that, especially as the current would be very slight, 
