Table 2. — Substituting successive values of R at intervals of .1, we have 



the foiioiving: 



Obviously, the value of R most closely approaching the true value is 

 2.5, since the value of |a of 3.99 is closest to the empirical value of 

 U.O. Considering the variability of our data, any interpolation of values 

 of R would be superfluous. Therefore, referring to the center line of 

 the table, we now have natural mortality and fishing mortality for the 

 two periods. 



DET'jIUvilNINa RITE OF RECRUITIENT 



To obtain the number of recruits entering the fishery each year, 

 we must first obtain the size of the available stocks for the tvro periods. 

 These may be computed from the total catch statistics, if it is known 

 what fraction the catch is of the available stock in each period. Ricker 

 calls this fraction, "rate of exploitation" (/u). Its value may be de- 

 termined from our previously computed values of total mortality (a), fish- 

 ing mortality (m), and natural mortality (n) as follows: 



m 

 AX = ffl + n (m + n - mn) (Ricker, p.60, par. 2) 



But also: a = m + n - ran (Ricker,.. p. 60, par. 1) 



am 

 Substituting: /u = ra + n (v) 



Using the numerical values of a, ra, and n given above, we have: 



_.kO(.3077)_ 



(V) /u^ = rjO?7 + .1333 ^ .2791 



. 80 r. 7692) 

 (V)/U2 = .7692 + .1333 = .6819 



Since yu represents the fraction of the stock caught by the .fishery, 

 the available stock (3j^) may be computed frora the catch (c) and rate of 

 exploitation (/u) by the siraple relationships: 



c = /u3^ or S^ =^ (VI) 



175 



