FLUCTUATIONS IN ABUNDANCE OF COLUMBIA RIVER 

 CHINOOK SALMON 1928-54 



INTRODUCTION 



Accurate evaluation of Lhe effect on the 

 fishery resources of large mainstream water- 

 use projects of the Columbia River still remains 

 a difficult and controversial problem . Attempts 

 to measure the effects of water -use develop- 

 ments on the salmon runs have been only 

 partially successful because direct effects are 

 intermingled with the effects of other influences 

 including the rapid encroachment of civilization 

 on the natural, primitive habitat of the fish 

 throughout most of the river basin. 



In this study an attempt to measure the 

 effect on the chinook salmon runs is made by 

 analyzing the catch -per -unit -of -effort in the 

 gill -net fishery of the lower river for a long 

 series of years before and after construction of 

 a specific water -use project, the Bonneville 

 Dam. Although records since 1928 of catches 

 of chinook salmon by gill -nets are available for 

 the calculation of the catch per unit of effort in 

 the fishery, certain influences should be taken 

 into account which may slightly distort the index 

 of abundance. Among these are (1) continued 

 expansion of the coastwise troll fishery, (2) 

 fishermen's strikes causing lapses in the data, 

 and (3) suddenly reduced fishing ability of gill- 

 nets such as occurred in 1940 when very low 

 water in the spring and summer contributed to 

 the bloom of a filamentous alga which clogged 

 the nets. 



This study is an extension and slight 

 modification of an earlier work (Silliman 1950) 

 which covered a period between 1935 and 1945. 

 Here the data are extended back to 1928 from 

 1954 for a 27 -year analysis. The returns are 

 divided into three separate groups --spring, 

 summer, and fall, and for comparison on these 

 annual totals, the three seasons are presented 

 in sum. 



Grateful acknowledgment is made to D. 

 R.Johnson, Supervisor of Research, Washing- 

 ton State Department of Fisheries, F. C. 

 Cleaver, former Assistant Director of Fisheries, 



Oregon Fish Commission, andH. B. Holmes, 

 Fishery Management Biologist of the Fish and 

 Wildlife Service, for their review and sugges- 

 tions in preparation of this manuscript. 



GENERAL BACKGROUND 



The following analysis is based on a 

 sampling technique . In planning the analysis, 

 certain limitations were required to keep the 

 problem within workable proportions . One was 

 limiting the analysis to catches of the most im- 

 portant species in the Columbia River, the 

 chinook salmon, Oncorhynchus tshawytscha. A 

 second was limiting it to the most consistently 

 successful type of fishing gear, the gill nets. 

 A third limitation used in the analysis was selec- 

 tion of a group of steady fishermen who would 

 con stantly provide data for comparisons based 

 on paired weeks from adjacent years . A fourth 

 limitation was the use of records only from gill- 

 net fishermen who delivered their catches in the 

 lower river. A fifth limitation was the assump- 

 tion that a fisherman's ability to sample a 

 population remained the same for two adjacent 

 years. And the sixth and final limitation was 

 the use of a test to identify fishing failures, 

 which will be explained later in this paper. 



The gill -net fishery caught approximately 

 64 percent of the total chinook catch from 1927 

 to 1934 (Craig and Hacker, 1940) and increased 

 to 70.7 percent from 1935 to 1946 (Johnson, 

 Chapman, and Schoning, 1948). Some who de- 

 liver their catch in the lower river continue the 

 employment of the original floater -type gill net. 

 Mesh sizes for catching chinook salmon generally 

 vary from 7 inches to 9-3/4 inches stretched 

 measure (Craig and Hacker, 1940). Another 

 type of net used in the faster current is the 

 "diver" net which has sufficient lead to sink it 

 to the bottom . A modification of the original gill 

 net is the "trammel" net which uses a smaller 

 mesh for catching a variety of sizes of fish. The 

 "trammel" originating in about 1900 is used 

 mostly as a "diver" type net. 



The Columbia River gill-net boat used by 



