HENRY: NATURAL AND FISHING MORTALITIES OF CHINOOK SALMON 



Table l. ^Estimated total recoveries of marked Columbia River hatchery fall 

 Chinook salmon of the 1961-62 broods. 



mortality rate for the 18-mo period from release as 

 smolts until the mature 2-yr-old fish return to the 

 river (Mj); 3) monthly natural mortality rates 

 for each year as 3-, 4-, and 5-yr-old fish (M2, M3, 

 and M4, respectively); and 4) proportion matur- 

 ing as 2-, 3-, and 4-yr-old fish im^, m^, and m^, 

 respectively). A few of these fish are caught as 2-yr 

 olds; however, to avoid further complicating the 

 analyses I have included these in the estimate of 

 Mj for the first 18 mo at sea. The number of 

 chinooks remaining at sea at the start of each year 

 (Ni, A^2. and N^) also can be calculated, but since 

 this had already been done for certain parameters 

 by Henry (1971), the calculations will not be re- 

 peated here. The D/s shown represent the number 

 of fish dying naturally. Thus, the entire initial 



Probabilities of 



group of smolts (A'^q) is either caught (C), escapes 

 into the river (E), or dies naturally (D), by the time 

 i - 1. The fishing season runs generally from 

 mid-April to mid-October. 



Mark recovery data used in this paper are listed 

 in Table 1. Catches of marked fish are estimates 

 based on sampling (see Worlund et al. 1969). Each 

 escapement is the total number offish returning to 

 the river and includes the river catch and returns 

 to the hatchery for a given mark. 



To expand the analysis used by Lander and 

 Henry (1973) from coho salmon to chinook salmon, 

 the events in Figure 1 can be depicted by a mul- 

 tinominal model with A^^ smolts falling into the 

 following seven observed categories with certain 

 probabilities O, {i = 1-8) as follows: 



£1 = ^1 = ^1 



,-18Mi 



Ci = 01 = (l-mi)e-i«^^^ie-6'^2 -^^ (l^-6(Fi+M2)). 



(1) 



(2) 



£2 = ^3 = (l-mi)e-i»^^ie-«^^^2^-(Fi.A/2) 



nxr 



C2 = O4 = (l-mi)e-i«^^V«^2e-6(Fi+A/2) ^X-m^)e'''''^ ^^ 



F2+M3 



(l_e-6<^2+^3)). 



£3 = 05 = (l-mi)c-l«^^le-6^2e-6(Fi+M2) (^.^^^ e-6M3g-6(F2+M3)^^ 



C3 = 06 = (l-mi)e-i«^^ie-6'^%-6<^i^^2)(i_^2) 



g-6M3g-6(F2+M3)^_^^)g-6M4 ^3 (^l.g-QiFs+M 4)^ 



i^3+Af4 



(3) 

 (4) 



(5) 

 (6) 



£4 = ^7 = (l-mi)e-i«'^V6^^2e-6(Fi+M2)(i_^^) 



g-6Af3g-6(F2+.W3)^_^^j^-6M4g-6(F3+M4) 

 £> = 08 = 1-01-02-^3-^4-^5-^6-^7 



(7) 



whereD = Di+D2+Ds+D4+D^+Dq+D-j = Total fish dying naturally. 



(8) 

 47 



