92 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The preceding table needs but little explanation. It indicates that the greater 
part of the young salmon from the fall run passed Balls Ferry between the middle 
of January and the middle of March. Practically all had passed by March 20. 
Measurements taken January 6, 13, 21, and 30, February 19, March 7, 15, and 31, and 
April 1, 2, 3, and 4 show that the average size of those taken on the dates specified, 
during a period of 34 months, varied but one-tenth of an inch. The average of all 
measurements is 1.53 inches. No satisfactory estimate of the number passing could 
be made, except that there were probably many millions. This record also proves 
that salmon fry begin migrating as soon as they are able to swim, and that practically 
all start downstream at that age, otherwise the later ones would have been larger. 
It was also ascertained that a large migration was not coincident with remark- 
ably high water. It is probable that when the fry once enter the main river their 
migration is not impeded by low water; but it seems probable, from observations 
noted in another place (see “Summer residents”) that many of the late fry that 
hatch in the headwaters are detained there during the summer by low water. 
Walnut Grove station . — Our knowledge of migrations through the lower part 
of the river was gained from the general investigation of 1898, and especially from 
observations made by means of a trap established at Walnut Grove from January 
to May, 1899. This trap was constructed especially for the work, but was hardly 
more efficient than traps made from seines and used at Battle Creek and Balls Ferry. 
It consisted of a bag with a short funnel hung to a 4-foot hoop, with wings 20 
feet long. At Walnut Grove the Sacramento makes a sharp bend, changing its 
direction from southeast to southwest. At this bend Georgeanna Slough breaks off 
and continues the southeasterly direction of the river above. It thus gets a large 
amount of water, probably half as much as the river below, and is in the direct 
path of the migrating fry. The trap was set about 150 yards from the head of the 
slough, which at that place is about 75 feet wide and 15 to 20 feet deep. The banks 
are abrupt and covered with bushes. One end of the trap was fastened by a long- 
rope to a tree on the bank, the other to a buoy anchored about the middle of the 
stream. It was sometimes set in other positions in the slough or in the river, but 
without results of particular value. During a sudden rise in the river it could not 
be set on account of the great amount of trash in the water. 
The following gives the record of the catch. In the column headed “A. M.” is 
given the number of fry found in the trap at 8 a. m., and in the “P. M.” column 
the number caught between noon and 5 p. m. 
Record of salmon fry taken in the trap at Walnut Grove. January 7 to May S. 1899. 
