RICHARDSON: SPAWNING BIOMASS AND EARLY LIFE OF NORTHERN ANCHOVY 



in the CalCOFI program (Smith 1972; Pacific 

 Fishery Management Council footnote 2). It re- 

 lates the census estimate (C^ or Q^) of northern 

 anchovy larvae to spawning biomass by means of a 

 regression. Smith (1972) demonstrated that in the 

 CalCOFI survey area the annual regional census 

 estimate (sum of four quarterly estimates) of lar- 

 vae is related to northern anchovy spawner 

 biomass in the following way: 



B, = 0.098 L, 



(9) 



where B^ = anchovy spawner biomass in short 

 tons 

 La = annual regional census estimate of 

 larvae x 10^ which is the sum 

 of the four quarterly census esti- 

 mates. 



This equation was based on yearly data from 1951 

 to 1966 and 1969, with the zero intercept forced, 

 giving 18 data points. Data, upon which Smith's 

 ( 1972) equation was based, can be used to obtain a 

 modification of this relationship, applicable to this 

 study, if certain assumptions are met, or can be 

 accounted for: 1) the same relationship between 

 census estimates of the number of northern an- 

 chovy larvae and northern anchovy spawning 

 biomass exists in the northern subpopulation as in 

 the central and southern subpopulations; 2) the 

 larva census estimate obtained from one cruise at 

 the time of peak spawning during the shortened 

 spawning season in the northern subpopulation is 

 equivalent to a quarterly census estimate made 

 during the peak spawning period, i.e., winter or 

 spring quarter ( Ahlstrom 1967) in the central sub- 

 population; 3) conditions, primarily temperature, 

 which influence development time and therefore 

 length of planktonic life, are similar in the north- 

 ern and central subpopulations for the time 

 periods considered; 4) sampling in the two survey 

 regions is similar; 5) spawning frequency during 

 the time period considered, i.e., during one quar- 

 ter in the central subpopulation and during the 

 2 -mo spawning season in the northern subpopula- 

 tion, is the same in both areas. 



Data from the Pacific Fishery Management 

 Council (footnote 2) on quarterly larva census es- 

 timates for the central subpopulation for winter 

 and spring quarters (Table 1) were regressed on 

 spawner biomass estimates for the years 1951 

 through 1966 and 1969, 1972, and 1975, with the 

 zero intercept forced, giving 20 data points each. 



Winter quarter: Ba = 614 + 0.152 L^; 



_0 /-» I-I/-1 



(10} 



r2 = 0.70 



Spring quarter: B„ = 645 + 0.151 L. (11) 

 r2 = 0.72 



where L^. = the winter quarterly regional census 

 estimate of northern anchovy 

 larvae 

 Ls = the spring quarterly regional census 

 estimate of northern anchovy 

 larvae. 



Because Smith's (1972) equation yielded a spawn- 

 ing biomass estimate in short tons, the values 

 obtained in Equations (10) and (11) are also in 

 short tons and may be converted to metric tons (t) 

 by multiplying by 0.9078. Larvae in my study 

 were collected with a 0.333 mm mesh net instead 

 of the 0.55 mm mesh silk net upon which CalCOFI 

 larva census estimates are based (Lenarz 1972; 

 Pacific Fishery Management Council footnote 2). 

 To correct for the increased retention by the 

 smaller mesh net, larva census estimates were 

 divided by the factor given by Lenarz (1972): 



C. 



C 



kr 



Cl corrected = — or Ct^ corrected = 



1.7 L7 



Thus, in my study I assumed that 



Lj^, = Lj = C^ (or Ckr) corrected 



(12) 



(13) 



T.'VBLE 1. — Census estimates (units x 10') of Engraulis mordax 

 larvae in the central stock for winter and spring quarters and 

 spawner biomass estimates ( in 1(P short tons) of the central stock 

 [from Pacific Fishery Management Council (text footnote 2) A. 14 

 and A. 15] from which Equations (10) and (11) were derived (see 

 Methods section). 



861 



