100 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
able to live in sea water they can not go directly from fresh water to sea water, but 
must pass gradually; third, they are greatly aided by an alternation of densities such 
as is obtained by passing through an estuary. For these reasons it would not be well 
to plant fry in a stream that does not reach the ocean through an estuary. 
Change of color daring migration . — The color of young salmon depends much 
on the character of the water in which they live. Those in small, cold streams are 
much more dusky and have the parr marks strongly developed. They become 
lighter in color upon entering the main river. Those in brackish and salt water are 
bright silvery on the sides, with the back sea green. Parrs 4 to 6 inches in length, 
found in Battle Creek and similar places, have the sides bright silvery, the back 
olive brown, with the upper end of the parr marks making regular shadings along 
the back. Specimens 2.6 inches in length from Rodeo, San Pablo Bay, May 18, have 
distinct parr marks; 2.7 inches, from Benicia, May 13, have lost them. Sometimes 
the caudal fin is reddish; sometimes there are yellowish stripes on the ventral and 
anal fins, especially with fry about 1.5 inches long. 
Summary of observations on migration . — The fry begin their downstream migra- 
tion as soon as they are able to swim. In the Clearwater they travel more at night; 
in muddy water, as much or more during the day. Much of the time they float 
downstream tail first, and in the larger streams they travel more or less in schools. 
In the larger streams their downstream movement is not dependent upon the height 
of the water, but upon age. From October to April, inclusive, over 99 per cent that 
pass the vicinity of Battle Creek are of the same size, 1.5 inches long. They pass 
down the river at the rate of about 10 miles a day, and are about 6 weeks reaching 
brackish water, being 3 months old at that time. They are probably 4 or 5 months 
old when they reach the ocean. The ebb and flow of the tide in the estuary, causing 
an alternation in the density of the water, is apparently beneficial. 
SUMMER RESIDENTS IN THE RIVERS. “ 
General account . — In the upper portion of the Sacramento River there yet 
remained, after the winter and spring migration in 1898, a large number of young 
salmon. In the vicinity of Sims we found from 700 to 1,000 in the various pools. 
We found them common in the McCloud at Baird in September, and in Fall River 
in August. These summer residents, as they may be called, are confined to the 
headwaters — the clear streams with rocky bottoms. They do not stay much of the 
time in the very swift current or riffles, but remain in the more quiet pools. Here 
they feed on aquatic insects and take the angler’s fly the same as trout. 
Most of the data concerning the summer residents was obtained from investi- 
gations near Sims, in Hazel Creek, and the river below its mouth. Hazel Creek is 
a small mountain stream, with many pools and gravelly riffles, and is a favorite 
spawning stream both for salmon and trout. The two lower pools, which are about 
a quarter of a mile from the mouth, were seined several times during the summer 
and fall, and it was from this work that we learned much that we know of the habits 
of the fry remaining in the streams during the summer. In the table below one of 
these pools is called the upper and the other the lower. 
The Sacramento River in the vicinity of Sims is about 40 or 50 feet wide, and 
during the summer has an average depth of about 3 feet. It is very swift except 
ii These notes on the “ summer residents ” are given largely as a matter of record. While the conclusions drawn 
in some cases are scarcely warranted, yet the available data point toward them, and too many of the estimates closely 
approximate each other to be the result of mere chance. 
