FISHERY BULLETIN: VOL. 84, NO. 3 



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JUL RUG SEP OCT NOV DEC JAN FEB MflR RPR HAY JUN 



MONTH 



Figure 1.— The monthly percentages of northern anchovies with 

 unknown sex, by age group, in samples from the San Pedro fishery. 



duced essentially no change in the sex ratio in the 

 sea survey data (1.02:1). However, there was a 

 reduction in the proportion of females in the fishery 

 data (1.48:1) which was associated with a reduction 

 in the average age of anchovy in the catch after 1977 

 (Mais 1981). Sunada and Silva (1980) also found a 

 female:male sex ratio greater than unity in the 

 northern Baja California purse seine fishery, 2.15:1 

 in 1976 and 1.44:1 in 1977. Alheit et al. (1984) 

 reported a sex ratio of 1.30:1 in purse seine caught 

 Peruvian anchoveta sampled during their spawning 

 season. Klingbeil (1978) and Alheit et al. (1984) 

 reported that during the spawning season there 

 were unexpectedly large numbers of samples in 

 which sex ratios were heavily dominated by either 

 males or females. Alheit et al. (1984) suggested that 

 "hydrated females segregate, either by depth or 

 area, from the 'normal' school, taking a high per- 

 centage of males with them forming 'spawning 

 schools' dominated by males." 



Analysis of the sex ratio by size and age groups 

 shows that there are increasingly larger proportions 

 of females in the larger and older groups (Table 2). 

 This trend is evident in both the fishery and sea 

 survey data. In the fishery data there are more 

 males than females identified in the fish smaller than 

 100 mm SL and in age group 0. The proportion of 

 females increases until there are more than twice 

 as many females as males among fish larger than 

 130 mm and in age group 4 + . There is a similar 

 trend in the sea survey data; however, females do 



not outnumber males until the fish are larger than 

 120 mm and 3 yr of age. The sex ratio in age group 

 4+ is 1.66:1. The apparent dominance of females 

 in the larger size classes may be partially caused by 

 sex related differences in growth rates; however, 

 their dominance in the older age classes of both the 

 purse seine and midwater trawl samples cannot be 

 explained by differences in growth. We grouped our 

 data sets into the spawning months (February- April) 

 and nonspawning months (August-December) in 

 order to evaluate features which might be caused 

 by behavioral differences that may occur during the 

 spawning season. This analysis shows that the over- 

 all sex ratio in northern anchovy taken by midwater 

 trawl is close to 1:1 in both nonspawning and spawn- 

 ing seasons (Table 2B). It also shows that the sex 

 ratios in younger fish are dominated by males and 

 those in older fish are dominated by females. The 

 overall sex ratio in northern anchovy sampled in the 

 purse seine fishery is heavily dominated by females; 

 however, the sex ratio is higher in the nonspawn- 

 ing season (1.58:1) than in the spawning season 

 (1.30:1). The crossover from male to female domi- 

 nance of the sex ratio occurs between age group 2 

 and 3 in the sea survey data and at age 1 in the 

 fishery data. 



MATURITY STAGES IN 

 NORTHERN ANCHOVY 



Seasonal Variation in Maturity Stages 



To determine which of the various data sets avail- 

 able for northern anchovy were best suited for 

 evaluating maturity stages in the central stock, we 

 examined the seasonality of three grouped matur- 

 ity stages of four data subsets. The grouped stages 

 included immature or resting females (stages 1 and 

 2); females just beginning to mature (stage 3); and 

 the highly mature, spawning, and spent females 

 (stages 4-7). The data consisted of two sets of 

 samples from the commercial fishery (Monterey and 

 San Pedro) and the sea survey samples from south- 

 ern California (lat. 32.5°-34.5°N) and northern Baja 

 California (29.5°-32.5°N). 



The seasonal patterns of the grouped maturity 

 stages of females sampled in the San Pedro fishery 

 (Fig. 2A), the sea survey in southern California (Fig. 

 2B), and the sea survey in northern Baja California 

 (Fig. 2C) are quite similar. The pattern in the Mon- 

 terey fishery differs from that in the other data sets 

 in that spawning is at the highest levels in April and 

 September (Fig. 2D). It cannot presently be deter- 

 mined if there are one or two peaks of spawning in 



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