FISHERY BULLETIN: VOL. 79, NO. 2 



whereas Hunter and Macewicz (1980) estimated 

 for 1979 that 50% of females of 96 mm SL were 

 mature. Laroche and Richardson (1981) reported 

 that only 31% of females 85-100 mm SL from the 

 northern stock were mature. Thus, size at sexual 

 maturity varies between subpopulations and may 

 have varied within the central subpopulation over 

 the last decade. 



The relatively short 2-mo spawning season of 

 the northern subpopulation of northern anchovy 

 (perhaps 4 to 8 spawnings, Hunter and Macewicz 

 1980) compared with the central subpopulation 

 (20 spawnings) is evidence of the great plasticity 

 in the annual number of spawnings. Plasticity in 

 the number of spawnings of the central stock is 

 also indicated by the dynamics of the central 

 population over the last decades. Smith (1972) 

 pointed out that the decline of the Pacific sar- 

 dine population was accompanied by an increase 

 in the duration of the northern anchovy spawning 

 period. Before the Pacific sardine decline, most 

 northern anchovy spawning occurred in the win- 

 ter quarter, whereas now larval production in 

 both quarters is about equal. This increase in the 

 duration of the peak period of spawning indicates 

 that the annual number of spawning batches 

 produced by northern anchovy has changed sig- 

 nificantly since the demise of the Pacific sardine 

 population. Food made available by the collapse of 

 the Pacific sardine population may have been used 

 by the northern anchovy population to increase 

 the number of spawning batches produced annual- 

 ly. The fact that these additional spawnings 

 occurred during the period Pacific sardine nor- 

 mally spawned may have had an important effect 

 on the Pacific sardine population. 



The annual seasonal decline in egg size in 

 northern anchovy population (central stock) re- 

 sembles that reported for other clupeoid fishes 

 (Blaxter 1969; Ciechomski 1973; Le Clus 1979). 

 Production of smaller eggs late in the season may 

 be an energy-sparing mechanism whereby fecun- 

 dity is maintained constant but at a lower 

 reproductive effort. This could represent a 20% 

 savings in reproductive costs in northern anchovy. 

 Bagenal (1973) concluded in his review of the 

 literature that it seems likely a negative correla- 

 tion exists between fecundity and egg size. Several 

 other mechanisms are possible; egg size may 

 increase with female age (Hirshfield 1977), and 

 the seasonal change could be caused by seasonal 

 changes in the age structure of the spawners. In 

 this case smaller eggs may compensate for the 



energy cost of faster growth in young fish. Alter- 

 natively, egg size may decline in females as ration 

 increases during the spring and summer. Bagenal 

 (1969) found that higher ration in brown trout 

 resulted in more and smaller eggs. On the other 

 hand, Hislop et al. (1978) found that the dry 

 weight of eggs produced by haddock in the labora- 

 tory declined with successive spawnings and that 

 the dry weight of eggs tended to be lower in 

 females fed a lower ration. In northern anchovy, 

 there may be a change in the partitioning of 

 energy between growth and reproduction during 

 late spring and summer when the potential for 

 growth is higher, and this could result in the 

 production of smaller eggs. As egg size alters 

 the survival potential of the larva (Blaxter and 

 Hempel 1963), any of these mechanisms could 

 have important consequences because it could 

 alter the relative contribution to recruitment of 

 spawn produced in the latter part of the spawning 

 season. 



Egg cannibalism may also be an important 

 factor regulating the effective egg production, as 

 intensity of cannibalism could change with popu- 

 lation size. Hunter and Kimbrell (1981) concluded 

 that ingestion of eggs by northern anchovy could 

 account for 17% of the daily egg production during 

 peak spawning months. 



This discussion indicates that egg production 

 and reproductive effort of northern anchovy popu- 

 lations probably changes in a complex manner in 

 relation to food, growth, temperature, population 

 size, and age structure. All the reproductive 

 parameters we have discussed may vary to some 

 degree over years, between subpopulations, or 

 within a season. 



Studies of the reproductive energetics of north- 

 ern anchovy populations will eventually require 

 consideration of males as well as females. We 

 know little about males at present. Our laboratory 

 data indicated that males consume slightly less 

 food than females, but no difference existed when 

 consumption was expressed on a unit weight 

 basis. Growth curves for male and female north- 

 ern anchovy (Collins 1969) indicate that females 

 are slightly longer than males of the same age, but 

 the difference is small (about a 2% difference in 

 length) and probably not statistically significant. 

 Other than this small difference in size, no obvious 

 sexual dimorphic characters exist. Schools have 

 highly biased sex ratios (Klingbeil 1978), and 

 males predominate in actively spawning schools 

 (Hunter and Goldberg 1980). This suggests that 



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