TABLE 6 



CALCULATED ESTIMATES OF AVAILABLE SQUARE YARDS OF SLTTABLE 5PAVJNING GRAVEL 

 FOR BLUEBaCKS in THE OKANOGAN RIVER COMPARED TO 

 POPULATION ESTIMATES DURING 19U?-5l 



Year Number of Fish Square yards of Square yards 



gravel utilized of potential 

 using dlk sq, yds, gravel avail- 

 per pair able, 



19U7 18,125 76,000 601,000 



19U8^ 35,875 151,000 6oi,000 



19U9 310 1,300 601,000 



1951 12,2i|0 51,000 601,000 



Although the seeding of spawning gravels continues to improve as exem- 

 plified by the escapements past Rock Island Dam, the survival of the young 

 fish plays an important part in determining the ultimate return and this can 

 vary within wide limits. Exceptionally cold weather and reduced flows can 

 damage the eggs of alevins by freezing and dehydration. Ice jams may scour 

 out the gravel before the young fry are in the free-swimming stage. 



During the winter of 19li7-U8 information was obtained concerning the 

 early life history of the bluebacks in the Wenatchee and Okanogan systems. 

 Redds were selected and marked with an iron pipe driven into the stream bed. 

 Periodic inspections were made during the winter while the spawn was in the 

 gravel. A very small, spoon-like blade was used on an ordinary shovel handle 

 and a fine-mesh hand-net held directly downstream from where the shovel was 

 thrust into the gravel. The information derived from this study is shown in 

 tables 7 and 8, 



As a result of the spawning-bed inspections we thought that the young 

 of the 19li7 brood fared well with one exception. On March 3, 19^8, dead 

 eggs were found in the Okanogan River. On fiorther investigation it was found 

 that the river flow had been shut off at the control gate upstream just below 

 Lake Okanogan for about a week while the dam and fishways were being rebuilt 

 at Zosel Dam, Oroville, Washington, This probably was a contributing factor 

 which resulted in smaller spawning counts in the Okanogan in 195l, despite 

 larger Rock Island counts. No nest inspections were carried on during the 

 winter of 19i|8, but it is a matter of record that the blueback areas were 

 subject to exceptionally cold weather during that winter. 



2/ Based on a ratio with 19li7 counts. 



20 



