FISHERY BULLETIN: VOL. 84, NO. 3 



hydrated eggs. Hunter and Macewicz (1980) showed 

 that northern anchovy begin hydrating eggs at about 

 0600 in the morning and by sunset about 14% of the 

 females have hydrated eggs. They felt that the best 

 indicator of the time of spawning was the occurrence 

 of both hydrated eggs and new postovulatory 

 follicles. This occurred in a low percentage of their 

 samples indicating that spawning was completed 

 rapidly; the time of maximum spawning occurred 

 between 2100 and 0200 with a peak between 2200 

 and 2300. Hunter and Macewicz (1980) divided the 

 nightly pattern of spawning in anchovy into three 

 periods: "early spawning period (1800 to 2100 hours), 

 some spawning occurs but the ovaries of most 

 reproductively active females are in the hydrated 

 stage; maximum spawning (2100-0200 hours), most 

 females spawn (females with hydrated eggs decline 

 to and females with new postovulatory follicles 

 reach the maximum number for the night); and post- 

 spawning (0200-0600 hours), little or no spawning 

 occurs and females destined to spawn the next night 

 begin hydration." A considerable amount of new 

 histological data is now available as a result of a 

 series of egg production biomass surveys for north- 

 ern anchovy. B. Macewicz (fn. 3) has analyzed the 

 histology of the ovaries of 8,672 anchovy sampled 

 in these surveys, and our analysis of this new infor- 

 mation verifies the temporal patterns which Hunter 

 and Macewicz (1980) described from a much smaller 

 sample (Fig. 5). 



Comparison of Maturity Stages and 

 Histology Classes 



The histological data show that during the early 

 evening the percentage of females with hydrated 

 eggs could be an indicator of the percentage of 

 females spawning per day (i.a, the spawning in- 

 cidence). To use the extensive maturity stage data 

 available for northern anchovy it is necessary to 

 determine the relationships between the histology 

 of the gonads and the maturity stages used in the 

 California Department of Fish and Game's sampling 

 programs. To date histological and field maturity 

 stage data have not been taken on the same individ- 

 uals; therefore, analysis is limited to comparisons of 

 the two data sets. In the following comparisons the 

 sea survey and histology data sets were limited to 

 samples taken during the period 1977-84 and dur- 

 ing the principal spawning season (i.a, February- 

 April). Since nearly all of the trawls were taken at 

 night, the data were limited to those taken from 1800 

 to 0500 h. The midwater trawl hauls were normally 

 15 min in duration, and about 30% of the fish in the 



JO 



en 



o 



in 



si 

 is 



10- 



5- 



UJ 

 d 



20 



15- 



£ 10- 



5 - 



HYDRATED 

 EGGS (H) 



t r 



DAY 



P0STGVULAT0RY 

 FOLLICLES (POF) 



I I -1 ' 



1800 2000 2200 2400 200 400 

 TIME OF NIGHT 



Figure 5— The percentages of female northern anchovies with 

 ovaries in three histological classes, by time of night. 



histological data set and 30% in the maturity stage 

 data sets were taken in the same trawl hauls during 

 cooperative cruises. 



The histological data are divided into six classes 

 (B. Macewicz fn. 3): 



1. Ovaries with hydrated eggs and no day-0 post- 

 ovulatory follicles. 



2. Ovaries with hydrated eggs and day-0 postovul- 

 atory follicles. 



3. Ovaries with day-0 postovulatory follicles and no 

 hydrated eggs. 



4. Ovaries with day-1 postovulatory follicles. 



5. Mature ovaries with no hydrated eggs, no day-0 

 nor day-1 postovulatory follicles. 



6. Immature ovaries, few or no yolked oocytes, no 

 atresia present in the ovary other than late-stage 

 corpora atretica. 



Northern anchovy, spawning on the night they were 

 sampled (day 0), include the first three classes; those 

 that spawned on the night before they were sampled 

 (day 1) are class four. 



A comparison of the percentages of hydrated 

 females in the sea survey data (i.e, stages 5 + 6) with 

 that in the histological data (i.e, classes 1 + 2) shows 

 that they have essentially the same pattern from the 

 onset of spawning in the early evening until spawn- 



510 



