FISHERY Bl'LLETIN VOL 77. NO 3 



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3 4 6 6 



NUMBER OF FEMALES 



DAY I 



POSTOVULATORY 



FOLLICLES 



0' I '2'3'4'66 

 NUMBER OF FEMALES 



Figure 3.— Frequency distribution of the numbers of samples 

 from February 1978 containing 0-6 females in each of three 

 reproductive classes (solid bars). On left sides of the upper two 

 panels are distributions for hydrated eggs and for day post- 

 ovoilatory follicles, compared with that expected (dashed linei 

 from the binomial distribution. On the right sides they are com- 

 pared with that expected from the negative binomial; the nega- 

 tive binomial gave the better fit in both cases. Bottom panel: the 

 frequency distribution for day 1 postovulatory follicles is com- 

 pared with that expected (dashed Imei from the binomial dis- 

 tribution, which gave an adequate fit to the data. 



the reproductively active females found by Clark 

 and Phillips ( 1952). They reported that only a few 

 females mature at 90-100 mm SL, about 309^ ma- 

 ture at 100-120 mm. and 50^; at 130 mm, whereas 

 all females we collected in February and March, 

 regardless of size, were sexually mature. Similar 

 to our observations. Brewer (1978) reported an- 

 chovy as small a.s 81 mm SL with well-developed 

 ova from San Pedro Bay. The size of anchovy at 

 first reproduction may have changed since 1946- 

 52 when Clark and Phillips made their observa- 

 tions. On the other hand, all of our collections and 

 those of Brewer (1978) were from southern 

 California whereas those of Clark and Phillips 



(1952) included collections from the north (Mon- 

 terey). It is possible that specimens living at the 

 northern end of the range of the central subpopu- 

 lation could be larger at first maturity. 



Incidence of Spawning 



Variation e.\isted in the percentage of females 

 occurring in the three reproductive states that 

 were indicative of imminent or recent spawning. 

 Of the females taken in February, 11% had only 

 hydrated eggs, 8'7f had new postovulatory follicles, 

 and \&7r had 1-day-old postovulatory follicles (Ta- 

 ble 2). It is critical to our objective of estimating 

 spawning frequency to consider which of these 

 states provided the better estimates. The distribu- 

 tion of the number of samples containing females 

 with hydrated eggs and that for females with day 

 postovulatory follicles gave a poor fit to the bino- 

 mial distribution indicating possible bias from 

 contagion within samples, whereas no such prob- 

 lem existed for 1-day-old postovulatory follicles 

 (Figure 3). Furthermore, evidence existed for a 

 bias in sampling females with hydrated eggs and 

 those with new postovulatory follicles that was 

 related to time of day (discussed below) and with 

 sexual composition of the school (tobe discussed in 

 a separate section). For these reasons, we believe 

 the 1-day-old postovulatory follicles are the pre- 

 ferred estimator of spawning frequency. 



Anchovy spawn only at night, and estimates 

 made by Smith** from staged eggs indicated that 

 most spawning occurs between 2000 and 0400 h. 

 Since hydration precedes ovulation and spawning, 

 one would expect the females with hydrated eggs 

 to be the most common before 2000. In February, 

 females with new postovulatory follicles were 

 probably undersampled and females with hy- 

 drated eggs possibly oversampled, because most 

 samples were taken before midnight. No females 

 with hydrated eggs occurred in the February col- 

 lections at night before 1900 h; six March females 

 taken in the morning showed the first signs of 

 hydration but the eggs were not sufficiently de- 

 veloped to be classified as hydrated. In February 

 the number of females with hydrated eggs in- 

 creased sharply after 1900 and generally re- 

 mained high until 2400 (Table 3). Females with 

 new postovulatory follicles occurred for the first 



'Smith. P. E. 1978. A field study of anchovy spawning 

 time Southwest Fish. Cent, Admin. Rep. No. LJ-78-H, I p. 

 Southwest Fisheries Center, NMFS. NOAA, P.O. Box 271, La 

 Jolla, CA 92038. 



646 



