FISHERY BULLETIN: VOL. 79, NO. 2 



this view. We conclude that, at least over the first 

 few months of spawning, the mean number of eggs 

 per spawning batch may be independent of past 

 spawning history. 



Size of Eggs 



The size of spawned northern anchovy eggs 

 varies seasonally as do those of other clupeoid 

 fishes (Blaxter 1969; Ciechomski 1973; Le Clus 

 1979). Smith and Richardson (1977) demonstrated 

 that the major axes of northern anchovy eggs 

 spawned in February 1972 were larger than those 

 of eggs spawned in August 1972 (P = 0.05). The 

 seasonal trend in dimensions of northern anchovy 

 eggs is illustrated in Figure 6 (upper). The dry 

 weight of eggs (calculated from their volume 

 (Equation (3)) varies by about 209^ over the 

 spawning season; thus, females could produce 

 about five more spawnings/yr at the minimum egg 

 size than at the maximum with no increase in 

 energy demand. The seasonal trend in egg dry 

 weight is similar to the relative larval abundance 

 (shaded area of Figure 6), with the largest eggs 

 produced in February to April when most of the 

 spawning occurs and the smallest eggs late in the 

 summer when the least spawning occurs. Several 

 possible explanations exist for the seasonal trend 

 in egg size. Females may produce smaller eggs as 

 the spawning season progresses or, alternatively, 

 large females which begin spav^ming earlier may 

 produce larger eggs than small females. Regard- 

 less of the mechanism, it probably is adaptive 



Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

 Month 



Figure 6. — Mean size of northern anchovy eggs taken in 

 routine plankton tows by month. Upper, mean major and minor 

 axes of eggs; lower, mean weight of eggs calculated from average 

 dimensions of eggs given in upper figure using Equation (3); 

 shaded area is the relative larval abundance for years 1953-60, 

 from Lasker and Smith ( 19771. 



to produce larger eggs early in the spawning 

 season when water temperatures are cooler since 

 the advantage falls to larger eggs as water tem- 

 perature declines, because incubation periods are 

 longer (Ware 1975). 



Maturation of Eggs 



Northern anchovy eggs <0.1 mm are spherical; 

 they become oblate spheroids between 0.1 and 0.25 

 mm (major axis) and thereafter retain the same 

 proportionality between axes through hydration 

 and spawning (Figure 7, upper). Hydration of the 

 spawning batch of eggs (rapid uptake of fluid) 

 begins about 12 h before spawning (Hunter and 



in 



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 90 



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MEAN MAJOR AXIS OF EGG (mm) 



1.4 



Figure 7. — The mean length of the mmor egg axis lupperi, 

 water content of the ovary (middle), and ovary wet weight of 

 a 16 g northern anchovy female calculated from Equation (6) 

 (bottom), as functions of the mean major egg axis of eggs in the 

 most advanced spawning batch (natural logarithms were usedt. 

 Original data for Equation (6) (solid line, bottom) given in 

 Hunter and Goldberg (1980); dashed lines indicate the range of 

 egg sizes that may hydrate; and they converge at the average 

 weight of a hydrated ovary in a 16 g female. Time scale on 

 abscissa is based on hypothetical rate of egg maturation required 

 for weekly spawning (see Figure 4). 



222 



