FISHERY BULLETIN: VOL. 74, NO. 1 



Table 5. — Incidence of monthly spawning activity by northern 

 anchovy as determined from larval counts. From Till- 

 man (1972). 



Month 



Fractional occurrence 



Adjusted occurrence' 



0.20 

 0.10 

 0.06 

 0.02 

 0.04 

 0.06 

 0.06 

 0.22 

 0.40 

 0.34 

 0.34 

 0.16 



'Adjusted to insure two spawnings per year 



Table 6. — Fecundity at age of northern anchovy, assuming 

 574 eggs/g body weight. From Tillman (1972). 



'Average weight in month 10, March, the midpoint of the major spawning 

 period. 



computed for each age group, which may be sub- 

 jected to a different total mortality, Z (A,M), 

 depending on natural mortality rate, catchability 

 coefficient, seasonal availability factor, and the 

 total units of standard effort operating upon 

 the stock during the month: 



Z(A,M) ^NM + F(AM) 



where NM = constant natural mortality rate 

 F(A,M) = age specific fishing mortality 

 rate 

 = Q(A)  AV(M)  FF(M) 

 where Q(A) = age specific catchability 

 coefficient 

 AV(M) = monthly availability of the stock 

 FF(M) = standardized level of effort. 



According to Schaefer (1967), NM = 1.10 and is 

 a constant parameter. Table 7 shows how catch- 

 ability decreases for ages which are not fully re- 

 cruited. Figure 3 indicates how availability varies 

 throughout the year, based upon extrapolations 

 of Messersmith's (1969) catch-per-unit-effort 

 (tons/hour) data for two seasons; this seasonal 

 pattern likely is associated with the spawning be- 

 havior of adults (Tillman 1972). 



Given these mortality rates, the catch of an- 



TABLE 7. — Age specific catchability coefficients for northern 

 anchovy given different areal restrictions and assuming full 

 recruitment occurs at age 2. From Tillman (1972). 



Age 



Coefficient when 

 inshore closed (10"^) 



Coefficient when 

 inshore open (10'^] 







1 



2-6 



0.24 

 2.78 

 9.04 



0.38 

 4.10 

 9.04 



.9 



.8 



.5- 



-I 1 1 1- 



-1 r 1 1 1 



Jon Feb Mar Apr May Jun Jul Aug Sepf Oct Nov Dec Jan 



Figure 3. — Average monthly availability of northern anchovy 

 in the southern California area. From Tillman (1972). 



chovy is then computed for the month subject 

 to the constraint that it may not exceed the reduc- 

 tion fleet's total or assigned harvesting capacity. 

 The fleet and natural mortality at first compete 

 exponentially to determine the number of fish 

 each would take if harvesting capacity were un- 

 limited. The temporary catch in numbers is cal- 

 culated as: 



CN(A) = 



F(A,M) 

 Z(A,M) 



N(A)  EXP 



where 



-ZiA.Mi iDT/NCYCLi 



EXP - 1 - e" 

 N(A) = size in numbers of age group 

 DT = 1 mo 



and F(A,M) and Z(A,M) are defined as above. 

 NCYCL is a parameter which determines the 

 accuracy of the solution and typically is set at 4, 

 yielding an effective DT of 1 wk. 



122 



