SMITH: SPAWNING BIOMASS OF NORTHERN ANCHOVY 



Table 11. — Anchovy larvae per positive station. 



Year 



No. of 

 positive 

 stations 



No. of 

 anchovy larvae 



No. of 



larvae per 



positive station 



of anchovy total larvae, and c is a constant rep- 

 resenting the relative fecundity of sardine rel- 

 ative to anchovy, here assumed to be approxi- 

 mately 0.5. Lenarz (1972) suggests a constant 

 of escapement of 1.1 to counteract the tendency 

 for anchovy larvae to pass through the mesh 

 openings of the standard silk net to a greater 

 extent than sardine larvae. This experimentally 

 derived estimate from paired tows which cap- 

 tured both species in standard and fine mesh 



nets is considered too small to be appreciable 

 on the scale of variability encountered in plank- 

 ton tows. Murphy's (1966) estimate of the 

 escapement factor, i.e., 2, is rejected. 



The equation for a least squares estimate of 

 the anchovy spawner biomass and anchovy total 

 larvae is: 



Ba = 0.094 La + 0.072 



defined in the same way as the sardine case 

 above. Similarly, the zero intercept was forced, 

 giving: 



Ba = 0.098La 



which is the equation used for the regression 

 estimate of anchovy spawner biomass. 



The aberrant years 1953 and 1959 were re- 

 calculated assuming the slope and the Murphy 

 sardine spawner biomass estimate are correct 

 and that the sardine larva estimates are biased 

 or imprecise. The recalculated estimates (pa- 

 rentheses, Table 12) appear to conform better 

 to the trends of anchovy biomass and anchovy- 

 sardine ratio. 



The data from 1940, 1941, 1950, and 1969 

 have been manipulated to extend the biomass 

 estimates. The 1940 and 1941 cruises were 



Table 12. — Sardine and anchovy spawner biomass estimates by ratio and regression methods. 



Murphy 

 sardine 

 spawner 

 biomass 

 (xl03T) 



Regression 

 sardine 

 spaw^ner 

 biomass 

 (xlO^T) 



Sardine 



larval 



estimate 



Anchovy 



larval 

 estimate 

 (xlO'2) 



Anchovy 



sardine 



ratio 



Ratio 

 anchovy 

 spawner 

 biomass 

 {xl03T) 



Regression 

 anchovy 

 spawner 

 biomass 

 CxlOn) 



* 1940, 1941 — larval estimates seasonally adjusted. 

 ** Parenthetic numbers for 1953 and 1959 assume larval numbers biased, 

 t 1969— larval counts 75% complete; adjusted for extra retention of small larvae. 



871 



