FISHERY BULLETIN: VOL. 79. NO. 2 



To estimate the rate of egg maturation required 

 for weekly spawning, we used the frequency 

 distributions of egg size in mature northern an- 

 chovy ovaries of females taken at sea. We mea- 

 sured distributions in 10 females taken in the 

 Southern California Bight in February 1979, and 

 in 6 taken in Monterey Bay in March 1979 by 

 Hunter and Macewicz (1980). Five of the females 

 from the Southern California Bight had 24-h-old 

 postovulatory follicles indicating spawning had 

 occurred on the day before they were captured, 

 and the other five were mature without evidence 

 of recent spawning. The ovaries of the six females 

 from Monterey were highly atretic and in post- 

 spawning condition, but had yolked eggs (Hunter 

 and Macewicz 1980). This latter group was used to 

 illustrate the condition of ovaries at the cessation 

 of spawning. Our method of measuring the egg 

 size-frequency distributions was similar to that of 

 MacGregor (1968). We counted and measured to 

 the nearest 0.05 mm all eggs >0.05 mm (major 

 axis) in a weighed sample of the ovary. 



Seasonal changes in fat content of female north- 

 ern anchovy were calculated using the original 

 data summarized by Lasker and Smith (1977). 

 Their samples were taken at roughly monthly 

 intervals from February 1965 to June 1967 ( n = 

 593). Their data, supplemented by additional data 

 (n = 338) taken in the summer and fall of 1979, 

 were used to estimate the relation between wet 

 weight without gonad ( W) and fat content (F) and 

 dry weight (without fat) (D). The multiple regres- 

 sion equation for this relation was 



W = -0.018 + 0.320 F + 5.469 D 



(1) 



where all variables are in grams, r^ = 0.969, and 

 n = 981. This equation permitted calculation of 

 wet weight of northern anchovy females after fat 

 gain or loss. Wet weight changes only slightly 

 with fat loss because water content increases as 

 fat decreases (lies and Wood 1965) (Table 1). The 



same data were used to establish the relation 

 between dry weight (without fat) (D) and stan- 

 dard length (L) where 



logio L = 0.313 logio D + 1.930, 



(2) 



r^ = 0.974. Thus, wet weight can be estimated for 

 northern anchovy of any standard length given 

 the fat content. 



Ahlstrom^ measured the major and minor axes 

 of 50-150 northern anchovy eggs taken in each of 

 58 standard ichthyoplankton tows (Smith and 

 Richardson 1977) along the coast of California and 

 Baja California in 1955, 1956, 1957, and 1965. 

 These data, combined with an additional 30 tows 

 (100 eggs measured/tow) taken in the same region 

 in 1969, were used to estimate seasonal changes in 

 the size of northern anchovy eggs. We calculated 

 monthly mean egg dimensions for the combined 

 data; number of tows per month varied from 9 to 16 

 (February- July) and from 1 to 4 in the period of 

 low egg abundance (August-December). We calcu- 

 lated the mean volume of the eggs per month from 

 average egg dimensions using the equation for a 

 prolate spheroid. The volume (V) in cubic milli- 

 meters was converted to dry weight (£■) in milli- 

 grams with the relation established in the lab- 

 oratory using freshly spawned eggs 



E = 0.0012 + 0.0930 V (3) 



where r^ = 0.646 and n = 32. 



Laboratory Data 



Three groups of northern anchovy of 1,200-1,300 

 fish each were matured in the laboratory to 

 measure the rate of ovarian maturation and to 

 estimate gross growth efficiency. The fish were 



^E. H. Ahlstrom, Southwest Fisheries Center, NMFS, NOAA, 

 La Jolla, CA 92038, unpubl. data, 1979. 



Table l.— Relationship between fat-free dry weight or length and wet weight for northern anchovy at the average season- 

 al minimum and maximum fat content. Relationships calculated from regressions; all body weights are without gonads. 



'From Equation (2) in text. 



^Percentage of the dry weight including fat. 



^From Equation (1) in text; 95% confidence Intervals calculated using Gauss multipliers (Snedecor and Cochran 1967). 



"[IV - (D + F)IW] X 100, where W = wet weight without ovary, D = fat-free dry weight, and F = weight of fat. 



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