WAHLE and VREELAND: BIOECONOMIC CONTRIBUTION OF FALL CHINOOK SALMON 



mission. We are assuming aging was correct (see 

 Assumptions). Therefore, we have assumed 

 marked fall chinook salmon with a double maxil- 

 lary or the wrong maxillary for a particular brood 

 were misidentified. Thus we claimed these 

 marked fish as part of the Columbia River hatch- 

 ery marked fall chinook salmon catch (Table 3). 



Therefore, estimated catches of Columbia River 

 hatchery marked fall chinook salmon (Tables 3, 

 8-14) include full, misidentified, and claimed par- 

 tial marked fish. 



Before estimating the contribution of hatchery 

 fall chinook salmon if no marking had taken place 

 (hereafter referred to as potential contribution), 

 the survivals of common marked fish had to be 

 calculated. Three methods were used to estimate 

 the common mark relative survival and a median 

 relative survival was calculated from the three 

 answers. 



METHOD 1.— All 13 study facilities were com- 

 bined and four sums — marked releases, un- 

 marked releases, marked returns, and unmarked 

 returns — were obtained for each brood year. The 

 marked to unmarked ratio at return was then 

 divided by the marked to unmarked ratio at re- 

 lease. The formula is: 



Marked returns 

 Unmarked returns 



Marked releases 

 Unmarked releases 



= Relative survival. 



METHOD 2.— If wild fish strayed into the study 

 hatcheries, diluting the marked to unmarked 

 ratios at return, method 1 would underestimate 

 relative survival. Thus to allow for straying, in 

 method 2 we have calculated relative survivals 

 using releases and returns from four selected 

 hatcheries. Cascade, OxBow, Little White Salm- 

 on, and Spring Creek, on streams with no 

 natural runs of fall chinook salmon. Relative sur- 

 vivals were estimated for each brood in the same 

 manner as described in method 1. 



METHOD 3.— Even for the four selected hatch- 

 eries, straying of wild fish into hatcheries is a 

 possibility, resulting in an underestimated rela- 

 tive survival. To account for this possibility, a 

 method was devised to estimate the number of 

 wild fish straying into the four selected hatcheries. 

 This was done in four steps. First, since the 

 selected hatcheries are between Bonneville and 



The Dalles Dams, an estimate of the maximum 

 number of fall chinook salmon spawning between 

 the dams was obtained by subtracting both the 

 Indian and sport fall chinook salmon catches be- 

 tween Bonneville and The Dalles Dams as well as 

 The Dalles Dam fall chinook salmon count from 

 the Bonneville Dam fall chinook salmon count. 

 Second, the maximum number offish spawning at 

 sites other than the selected hatcheries was ob- 

 tained by subtracting the four hatcheries returns 

 from the total spawners between the dams. Third, 

 the age of fish spawning at sites other than the 

 selected hatcheries was approximated by applying 

 age data from Columbia River gillnet fall 

 chinook salmon catches. Fourth, straying factors 

 (from observed straying offish marked at Spring 

 Creek Hatchery) were applied by brood and age to 

 the wild spawners to obtain the estimate of wild 

 fish straying into the selected hatcheries. These 

 estimates are maximum since we cannot account 

 for mortalities, uncounted fish passing through 

 navigation locks, double counting offish that fall 

 back over dam spillways and again ascend the fish 

 ladders, or fish straying from the four hatcheries. 

 Also, we assumed wild fish had the same straying 

 pattern as the hatchery fish in this study, i.e., they 

 strayed to sites near their area of origin. 



Once the brood estimate of the number of wild 

 fish entering the hatcheries was obtained, it was 

 subtracted from the appropriate unmarked re- 

 turns. The resulting unmarked hatchery return 

 quantity for each brood was then used in the for- 

 mula described in method 1 to calculate the third 

 estimated common mark relative survival. 



Examples of the calculations used to obtain the 

 three values for the common mark relative survi- 

 vals are presented by Worlund et al. (1969). The 

 median common mark relative survivals for the 

 1961-64 broods of Columbia River study hatchery 

 fall chinook salmon are: 



Special mark relative survivals also had to be 

 calculated to estimate contributions of special 

 marked hatcheries. Calculating special mark rel- 

 ative survivals for each hatchery was impossible 

 because seven hatcheries (Elokomin, OxBow, 



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