HUNTER and ROE THE SPAWNINC, ENERGETICS OK NORTHERN ANCHOVY 



population spawning per day indicates that either 

 the interval between spawnings in individual 

 females increases in the latter part of the spawn- 

 ing season, or that an increasing number of 

 females cease spawning as the season progresses, 

 or a combination of both events. Rates of egg 

 maturation and vitellogenesis probably also vary 

 within a single maturation-spawning cycle. The 

 caloric content of a northern anchovy ovary about 

 doubles over the interval between spawnings 

 (7-10 d in peak spawning months), indicating a 

 rapid rate of vitellogenesis after spawning. In 

 Brachydanio rerio, which spawns at 5-d intervals, 

 a marked increase in gonadotropic activity occurs 

 in the pituitary immediately after spawning 

 (Lambert and van Oordt 1974), followed 1-2 d 

 later by histological signs of an increase in lipo- 

 protein production in the liver correlated with an 

 increase in vitellogenesis (Peute et al. 1978). 

 Similar processes may occur in northern anchovy, 

 causing cyclic changes in the rates of vitello- 

 genesis and egg maturation within the interval 

 between spawnings. 



Our estimate of 20 spawnings/yr is much higher 

 than the number of spawnings estimated for many 

 other pelagic spawning clupeoid fishes or for 

 pelagic spawners in general. Multiple spawning 

 fishes such as pilchards, sardines, anchovies, jack 

 mackerels, and mackerels are often believed to 

 produce one to three and possibly more spawning 

 batches per year. These conclusions are based on 

 the fact that frequently two modes of yolked eggs 

 and sometimes three (in females with hydrated 

 eggs) are observed in frequency distributions of 

 ovarian egg sizes. Eggs are distributed in the same 

 way in the northern anchovy (MacGregor 1968; 

 Hunter and Goldberg 1980), but as present studies 

 indicate, estimates of one to three spawnings 

 would be in error by a factor of about 10. Thus, 

 comparisons of annual fecundity among pelagic 

 spawning clupeoids are meaningless at present, 

 and spawning biomass estimated from egg and 

 larval surveys may be in error because the total 

 fecundity is inaccurate. Because of this it is 

 essential that spawning frequency be estimated 

 for additional species. 



The best approach, at present, is the histological 

 technique of Hunter and Goldberg (1980), but 

 counts of the number of females with hydrated 

 eggs could be used if histological techniques are 

 impractical. Females with hydrated eggs are often 

 rare in collections of clupeoid females taken dur- 

 ing the spawning season (Higham and Nicholson 



1964; Leary et al. 1975). Females with hydrated 

 eggs may be available for sampling for only a short 

 period of each day because hydration is rapid and 

 spawning soon follows hydration. In northern 

 anchovy, hydration is completed in about 12 h, 

 but the earliest stage may not be evident with- 

 out histological examination. In tropical species 

 the time available for sampling females with 

 hydrated eggs may be even less because of ele- 

 vated temperature. The daily pattern of hydration 

 and spawning must be known to use hydrated eggs 

 as a measure of spawning frequency. It may also 

 require sampling offish in the day, because many 

 pelagic spawners such as the northern anchovy 

 begin spawning at sunset (Blaxter and Holliday 

 1963; Leary et al. 1975; Hunter and Macewicz 

 1980). 



Variation in Egg Production and 

 Reproductive Effort 



Annual egg production and/or reproductive 

 effort in northern anchovy populations can be 

 modulated by changes in batch fecundity, annual 

 number of spawnings, female size at first ma- 

 turity, egg size, and egg cannibalism. Some evi- 

 dence exists for each of these mechanisms in 

 northern anchovy populations; we consider the 

 evidence below. 



Batch fecundity was relatively constant over 

 1978-79 (Hunter and Macewicz 1980) and was 

 similar to that of laboratory specimens fed a large 

 food ration. On the other hand, MacGregor (1968) 

 estimated a somewhat higher fecundity for the 

 central stock in the 1950's than Hunter and 

 Macewicz (1980) did for the 1970's, and Laroche 

 and Richardson (1981) found that batch fecundity 

 of the northern subpopulation (Oregon coast) was 

 much higher than all estimates for the central 

 stock. Batch fecundity certainly differs between 

 central and northern subpopulations, and it seems 

 possible that it may have varied within the central 

 stock over the last decades. Nevertheless, batch 

 fecundity within a subpopulation may be a rela- 

 tively more stable reproductive characteristic 

 than other reproductive traits. 



Weight at first maturity and age structure of 

 the spav^Tiing population have a major effect on 

 egg production, since batch size in northern an- 

 chovy increases exponentially with weight. Clark 

 and Phillips (1952) concluded for females taken in 

 1946-52 from the central subpopulation that 50% 

 of northern anchovy reach maturity at 130 mm SL 



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