28 



U. S. BUREAU OF FISHERIES. 



iriavel from 1 to 4 inches in diameter. Here the eggs were huried from ap- 

 proximately 8 to 16 iiK'hes deep. When the eggs were reached, the gravel was 

 founil to he absolutely clean, more especially where the good eggs were secured, 

 with a coating of fine sediment on top, indicating a circulation of fresh spring 

 seepage water at all times. Anticipating this condition, a common trough 

 was installed in the slough, with a circulation of fresh water assured at a low 

 tide, hut which at flootl periods would be covered from lA to 4 feet wilh salt 

 water without any circulation. The trough was filled with gravel, through 

 which about 25,000 eggs were carefully mixed. A tight cover was then 

 fastened on the top. with sufhcient space left at both ends for proper circula- 

 tion. The eggs were placed in the gravel on December 18, 1919, inunediately 

 after being fertilized, and on examination, on March 5, 1920, they were found 

 to have hatched with an estimated lo.ss of about 30 per cent. The fry appeared 

 to be extremely active and healthy. The had eggs were nearly all decayed 

 and broken but had the appearance of having been fertilized and the embryo 

 partially developed. 



This would lead us to believe that an entire salt-water supply, with as low 

 a density as 1.010 for an extended period, is injurious but not absolutely fatal, 

 and it strengthened our belief that where fish spawn naturally within tidewater 

 area the eggs are deposited wliere they receive a circulation of fresh water, as 

 before stated. Samples of eggs were taken from each nest, and, contrary to 

 Mr. Robertson's theory and observations in hatching eggs in gravel, the infertile 

 eggs were chalky white when first observed in the gravel. The alternathig 

 salt and fre.sh water may be a contributing cause, though where a continuous 

 circulation of fresh water seeps through the gravel it would ajipear dillicult 

 for salt wafer to penetrate sulKciently to have mucli influence on the eggs. 



'Our observations led us to believe that the infertile eggs might be accounted 

 for largely by a scarcity of male salmon. However, there is a possibility that 

 spawning might have occurred wholly in salt water, which may prevent the 

 action of the eggs necessary to proper fecundation. As all but a few of the 

 fish entering the slough were taken in the trap, and as the males are usually 

 the first to ascend, it is not improbable that most of the males entered the 

 trap, thus reducing the possibility of successful natural spawning at the points 

 where observations were made. The table would indicate enormous losses 

 through natural spawning, but as conditions were not absolutely normal, we 

 would not care to he too emphatic from this meager survey. 



To obtain full information relative to the foregoing it would be necessary 

 to extend observations over the entire spawning season. Each nest should be 

 marked and accurate data produced as to the number of fish depositing in each 

 nest, together with all natural and unusual occurrences noted. 



Results of Examinations of P'isii Nests. Walcott Slough, Brinnon, Wash., 



March 5, 1920. 



1 The Slit witer density was tested by pumping water from bottom over nests at flood tide and ranged 

 froml.OlSat bo.x location to 1.022 at nests Nos. 1, 2, and 3, and 1.025 natural sea water in Hood Canal. 



2 Planted. 



' Nests 5 feet apart. 



* Current swift and water badly discolored; numbers estimated from those seen in the water and caught 

 In net and baskets set below the nests on the riffles when disturbing eggs; good eggs are not as buoyant as 

 dead ones, and therefore some may have escaped our notice. 



