SMITH: SPAWNING BIOMASS OF NORTHERN ANCHOVY 



by 2 to obtain the number of eggs produced [in one 

 spawning]^ by one ton of adult fish. If we further 

 assume that .... about half the [adult] sardine pop- 

 ulation spawns twice [a year] (average iy2 times) 

 and the anchovy [adult] population spawns 2 or 3 

 times a year (average 2V^ times), we would also 

 multiply millions of eggs by IV2 for the sardine and 

 2% for the anchovy. On the above basis the total 

 number of eggs produced by one ton of adult fish of 

 both sexes in one year would be as follows for each 

 species : 



Species 

 Anchovy 



Sardine 



Millions of eggs 

 656 



181 



It may be seen from the above that, although numbers 

 of eggs or larvae in the plankton may be used as an 

 index of adult abundance, a sardine egg in the plankton 

 represents 3% times ... as much adult biomass as 

 an anchovy egg. Estimates of the average biomass 

 of each . . . species for the 3-year period 1955-57 and 

 the average commercial landings for the same period 

 are as follows: 



Sardine 



254,000 



51,508 



* Anchovy larvae caught were used as an estimate of eggs. This may 

 have resulted in underestimation by a factor of 2. Application of thii 

 factor brings this biomass of anchovies into line with the material in 

 Murphy's (MRC, 1964) estimate of the anchovy harvest .... 



" In brackets added for clarification. 



In another informal statement Radovich 

 (MRC, 1965) cited the change in anchovy to sar- 

 dine larval ratios (Ahlstrom, MRC, 1964) and 

 stated "... in this 8-year period the anchovy 

 maintained its population level fifteen times bet- 

 ter than the sardine . . . ." He further pointed 

 out that the necessary ratio of annual survival 

 rates to attain this was 1.4. Should this dif- 

 ference in survival be in the larval stage, the 

 MacGregor (MRC, 1964) biomass estimate 

 should be divided by 1.4 or roughly 1.5, resulting 

 in an estimate of about 1 million tons. 



Murphy (MRC, 1964) used an anchovy 

 spawner biomass estimate which was essentially 

 double MacGregor's (MRC, 1964) because he 

 believed that the escapement of anchovy larvae 

 through the mesh of the standard CalCOFI silk 

 net exceeded the escapement of the sardine lar- 

 vae enough to cancel the effect of anchovy fe- 

 cundity exceeding sardine fecundity. Thus 

 Murphy's calculation (1966, p. 60) of anchovy 

 spawner biomass for the period 1955-57 was 3.3 

 million short tons as compared to MacGregor's 

 1.5 million short tons and Radovich's 1.0 million 

 short tons for the same 3-year period. An esti- 

 mate by Murphy's method for 1958 would be 5.1 

 million short tons. 



Ahlstrom (1968) estimated that the 1958 an- 

 chovy biomass was between 1.80 and 2.25 million 

 short tons and observed further that the biomass 

 had reached a plateau of 4.5 to 5.625 million 

 short tons in the mid-1960's. 



Table 1. — Comparison of data used for estimating the spawning biomass of northern anchovy. 



Standard 



haul 



summation! 



Summation 



of. average 



quarterly estimatesZ 



Larval census 

 estimates' 



Standord haul 

 summations* 



851 



