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Page:Popular Science Monthly Volume 61.djvu/211

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salmon. In the vicinity of Sims in 1898 we found 700 to 1,000 in the various pools. They were common in McCloud River 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 swift current or riffles, but remain in the more quiet pools, where they feed on insects and take the angler's fly the same as trout. Considerable effort was made to learn as much as possible concerning them, and Sacramento River near Sims and its tributary, Hazel Creek, were visited each month from May to December with that end in view.

During July and August, all specimens taken were marked by cutting off the adipose fin, by which means we were able to make estimates of the number in the pools, their rate of migration, and their rate of growth. The number estimates were made thus: After having marked a few and released them in the pool, the following proportion was formed with the data from each seine-haul: the number of marked fry taken is to the number of marked fry in the pool, as the total number taken is to the total number in the pool. In August, when we could distinguish those just marked from those marked in July, we were able to make estimates of the number of July-marked fry in a pool and, knowing the number released there in July, to compute the rate of migration for the month.

The following table gives the result of the work in one pool, and illustrates the data used in making the number estimates:

Date.  No. caught.   No. previously 
 No. marked 
fry caught.
 Estimated No. 
in pool.
 Aug. 16 P. M.   66   1  1
148  66 13  751
146 197 30  992
Aug. 17 A. M.  83 312 38  682
 47 357 19  883
 19 385  4 1804
 64 400 25 1024
149 439 62 1055
 71 525 40  932
 35 556 15 1297
Aug. 17 P. M.  19 576  9 1216
  3 586  3  586
—— ——
Total different individuals, Average of
24 hrs., 586 estimates, 1022

The average estimates for two other smaller pools are 685 and 861. From these estimates it seems probable that there were about 10,000 young salmon to the mile in the upper Sacramento during the summer of 1898, or less than a million in all the headwaters, which is a very