DAYS CARCASSES ON BOTTOM 

 DAY OF DEATH 



J \__ 



JULY 2 



JULY I ^- 



JUNE 30 -^— •- 



JUNE 29 ^^ 



JUNE 28 ^-' 



JUNE 27 ^^ 



JUNE 26 .b-^- 



JUNE 2 5 .^■^' 



JUNE 2 4 ^—f J- 



JUNE 2 3-^—' I I 



JUNE 22 .bi^' < I ( 



JUNE 2 I ^.^ -  



I JULY I 



JULY 9 ."-^ 

 I 



JULY B /— •-- 



JULY 7 If—r 



JULY 6 -^-^ 



JULY 5 -^"■--1 



JULY4 .^— -j 



JULY 3 —  [ 



i— -^ 





I PERCENTAGE OF CARCASSES 



RECOVERABLE ON 7TH THROUGH 

 I y I6TH DAY AFTER DEATH -7 



s<?> p ^ o,' 



^21 99 



.^ 



I 



— ' '7 7.46 i9 



—'8792 V^ 

 94,20 x?~l^o'^ 

 ^96,30 ^<»^' 



— 98 40 O'^.o"^ 



99.97 ,i^^ '^ 



=7 99 97 o>s<^ 



17 77 98 *\'Sf' 



=7 58.11 



.«?> 



:^ 22.51 ,^-v 



/ / 42.40 



^ 3L94 



,«^, -y 



=7 5.77 





-I ' 3.67 





J I I I L- 



T? s° ^0 



1.57 

 — II-DAY RECOVERY PERIOD - 



J I J I L 



J I L 



J I I U 



2 1 22 23 24 25 26 27 28 29 30 1 I 



JUNE 



8 9 10 I I 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 

 JULY 



Figure 7. — Availability of carcasses for recovery. When chinook salmon die, the carcasses sink to the bottom. Recoverable 

 carcasses may or may not float to the surface between 7 and 16 days after death. When a carcass floats, it can be re- 

 covered only on the day it floats. Percentages of recoverable carcasses that become recoverable on the 7th through 16th 

 days after death are given at the top of the figure, and the sums of these percentages falling within the 11-day recovery 

 period are given on the right diagonal edge for each date of mortality. 



X2 = 31, n. = 117 + 31 = 148, and p, = 31/148 = 

 0.2095. Substituting in equation (3) gives an 

 estimate of Yi: 



untagged recoverable carcasses. An approximate 

 95-percent confidence interval on p^ is 0.12 < 

 0.2095 < 0.33. The _ corresponding 95-percent 

 confidence interval on Yi is 2,373 < 4,412 < 8,572 

 untagged recoverable carcasses. 



It is clear from the preceding discussion and 

 from figure 7 that this estimate of 4,412 untagged 

 recoverable chinook salmon carcasses represents: 



(1.57 percent of the recoverable carcasses from 

 June 21 mortality) 



+ (3.67 percent of the recoverable carcasses 

 from June 22 mortality) 



-|- . . . + (21.99 percent of the recoverable car- 

 casses from July 10 mortality). 



PROPORTION OF CHINOOK SALMON 

 RUN KILLED 



To estimate the proportion of the chinook 

 salmon run killed near Bonneville Dam during 

 our experiment in 1955, we relate our estimate of 

 the number of recoverable carcasses in the river 

 below the dam (i.e., Yi = 4,412 recoverable car- 

 casses) to the size of the run producing these car- 

 casses. 



Two additional factors should be taken into 

 account. In our 1955 experiment, all tagged car- 

 casses were released immediately below the dam. 

 This situation would correspond to one in which 

 all chinook salmon mortality at the dam occurs 

 before the fish are counted over the dam. However, 



CHINOOK SALMON MORTALITY IN COLUMBIA RIVER NEAR BONNEVILLE DAM 



477 



