FEM.\LE SALMON (O. nerka) OF THE COLUMBIA RIVER 



431 



Table 1. — Incidence of small ($2) blueback in the Columbia 

 River since 1!)45 ' 



1 fiources of data: Bonneville Dam fishway counts.— From Annual Fish 

 Passace Report, North Pacific Division, Bonneville, The Dalles and 

 McN'arv Dams, Columbia River. Oregon and Washineton, 1958. U.S. 

 Corps of EnKinccrs. Portland and Walla Walla Districts. Also unpub- 

 lished data. 19.59. Catch below Bonneville Dam.— From Oreson Fish Cora- 

 mission, unpublished data. Rock Island Dam fishway counts.— From U.S. 

 Fish and Wildlife Serviw, Bureau of Commercial Fisheries, Portland, Oreg. 



Table 2. — The escapement-return data for the Columbia 

 River blueback runs for the brood years WS8-55 



Because the lack of more complete data pro- 

 hibits a comprehensive examination of the latter 

 two items, we shall examine only the first alterna- 

 tive in this report. If age ^o females were highly 

 abuiuiant in the 1953 escapement and if these 

 small females contain fewer eggs tlian norinal age 

 42 females, then tlie egg potential of that escape- 

 ineiit may have been iiuicli lower than the number 

 of spawners or even female spawiiers would 

 indicate. 



Our main objectives are, tiierefore: (1) to 

 estimate mean fecundity of the various age 

 groups that spawn in the Okanogan River and 

 (2) to assess the efl'ect of age and sex composition 

 on estimates of egg potential of tlie Okanogan 



River spawning escapements. In the light of our 

 findings, we siiall then examine and discuss other 

 aspects of the early maturing fish. 



Tiie assistance of the Oregon Fish Commission 

 aideil this study materially. The authors are 

 particularly indebted to Lawrence Korn for 

 collecting tlie ovary samples in 1958. 



METHODS AND MATERIALS 



Collection and Preservation of Samples 



Estimates of age group fecundity are from 

 fisli taken both in the tributary spawning streams 

 and in tiie commercial catcii below Bonneville 

 Dam on tlie main Columbia River. In 1957 the 

 racial sampling program of the International 

 Xorth Bacific Fisheries Commission made avail- 

 able to us 34 females taken at Tuniwater Dam on 

 the Wenatchee River and 23 captured at Zosel 

 Dam on the Okanogan River. Samples from tiiis 

 source were not available in 1958; thus we had 

 to find samples elsewhere, preferably from the 

 commercial catch to avoid killing potential 

 spawners in the tributaries. In 1958 sixty-two 

 fish were selected from the commercial catch to 

 represent the length-range of female blueback. 

 Similar sampling provided 27 fish in 1959. Owing 

 to a scarcity of small fisli in the catch, the 1959 

 catch sample was augmented with 10 small fish 

 taken from the fishway at Rock Island Dam. 



Members of the 42 age group from both the 

 Okanogan and Wenatchee areas are mixed in the 

 catch, and we have no method of classifying catch 

 samples into area of origin. Consequently, it is 

 necessary to assume that fecundity estimates 

 derived from this source accurately represent tjie 

 Okanogan River spawning population. A sta- 

 tistical test to support this assumption is presented 

 in a later section. 



From each fish the fork length was recorded 

 and a scale sample taken for age determination. 

 Ovaries were removed, wrapped in cheesecloth, 

 labeled, and preserved in 10-percent formalin. 

 Total, fresh-w'ater and ocean ages were determined 

 i)y the age analysis unit at the Bureau of Com- 

 mercial Fisheries Seattle Biological Laboratory. 



Egg Enumeration 



Estimation of total egg content for each fish 

 proceeded as follows: Each pair of ovaries was 

 washed of excess formalin, drained of excess 

 moisture, freed of tissue, then weighed to the 



