84 



Current Pall Chinook Total Run Size and Historical Levels 



Chehalis Basin Chinook abundance is within the same order of magnitude as that 

 reconstructed from historical catch data (Table 6), given the assumptions 

 outlined below. This suggests current run size is a base level of natural 

 production, to be reinforced by improving inner Harbor and upper Chehalis 

 water quality, and by assuring optimum wild escapement through refinements in 

 habitat assessment and fishery management. It is important that any hatchery 

 programs be enhancement, not replacement, of the base level. 



The following are assumptions supporting estimates of total Chinook run size 

 in Table 6. 



I- HISTORIC PERIOD 



The Gnyi Harbor Caleb Reporting Area noo-Indian gillnet catch, averaged over the period 1910-1919, plus pretest 

 Chehsli* Baaio spring and fall Chinook eacapemeat u a conaervative estimate of potential beahhy total run sue, baaed 

 on the following aaaumptiona: 



A. The Grays Harbor Catch Reporting Area represent**) the ffcrhalw Basin even though the Area included all 

 the riven of the aoTtbem Washingtoa coast to Cape Flattery. Catch recorda beginning in 1936 divided Graya 

 Harbor Area catch into only two categories: Grays Harbor co mmerc ial gillnet catch, and north coastal Indian 

 catch, thus implying thai: 



1. North coastal non-Indian catch was negligible in compariaoa to north coastal Indian catch; 



2. the Grays Harbor Indian catch was negligible in compariaoa to the Grays Harbor noo-Indian catch; and 



3. sport catch throughout the Area was negligible. 



B. The average catch from 1910 to 1919 represented a healthy not (following a method used by Chapman 

 (19&6~) for the Colombia River. 



1 . The 10-year catch avenging period is the shortest that results in an eaaily interpreted catch trend because 

 undue weight is not given to unusually high or low brood cycle*. 



2. The Grays Harbor noo-Indian gillnet catch tread increased from the initial 1890-1899 period, reached ha 

 highest value during the 1910-1919 period, and declinrd from then until now. This suggests: 



a. Fishing pressure increased to maximum efficiency until the peak period, and overfishing did not 

 seriously affect the population prior to the atari of catch reporting in 1890. 



b. Terminal area overfishing (Wendler and Deachampt 1955b) combined with the onset of splash dam 

 logging (Wendler and Deachamps 1955a) initiated a atock decline after the peak catch period. 



c. Bccsnsr marine interception became significant only after the peak period (Wendler and Deachamps 

 1955b), the peak period catch ia Kill a reliable estimate of total catch, if one accepta that: 



1.) Washington marine catch represents coastal marine fishing effort in general; and 



2.) Washington marine fishing increased at the same rate prior to inception of marine catch 



recorda in 1936 (WDF 1971), as it did during ha expansionary penod thereafter, i.e., it 



was negligible prior to the 1920s. 



C. Average hrtfnriral spawning escapements were similar to current escapements. 



n.CURRENT PERIOD 



Estimated terminal catch plus marine catch phu spawning escapement, averaged over 1987-1990, reasonably esunistes 

 total wild run size of Chehalis Basin fall Chinook, based on me following asaumptioas: 



A. The ratio of 1987-1990 marine area expanded tag returns to terminal area expanded tag returns multiplied 

 by the terminal area catch, adequately rsthnatrs marine enter teptiu n of Chehalis Basin chmook (Table 7). 

 This rests on four propositions: 



1. Terminal lag rtemtria rrprttau all ctmtmtmal talmon fiihrria . Any resulting upward bias in total 



catch would not be excessive since fall Chinook sport catch averaged only about eight percsat of the 

 terminal area catch (WDF, unpublished data). 



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