FISHERY BULLETIN: VOL. 79, NO. 2 



at end of feeding period. Similar functions have 

 been used by Tyler (1970), discussed and used by 

 Eggers (1977), and discussed by Elliot and Persson 

 (1978). The daily pattern of feeding and evacua- 

 tion and the data used to calculate the parameters 

 for the ration equation are given in Figure 1. We 

 use an exponential equation to estimate rate of 

 gastric evacuation (r) because it is required by 

 theory and the above model and use a linear 

 regression equation for gut filling because the 

 equation is used only to provide an empirical 

 estimate of the mean stomach contents ( s ) during 

 feeding. 



The mean ration for a feeding day was 0.0437 

 g/g body wet weight (group 2) and 0.0462 g/g body 

 wet weight (group 3); these values were multiplied 

 by the mean wet weight of fish sampled (18.6 g, 

 group 2; 17.6 g, group 3) to express the ration in 

 terms of the average fish weight in each experi- 

 ment. This value was adjusted by the ratio, total 

 number of feeding periods/duration of the experi- 

 ment (days) (ratio = 59/69, group 2; 67/78, group 

 3), to adjust the ration for days when no feeding 

 occurred. This daily ration for the experiment was 

 converted to calories by multiplying by 0.656 

 (average ratio of dry to wet weight for stomach 

 contents of northern anchovy fed Oregon Moist 

 Trout Pellets) and by 4,912, the caloric value per 

 gram for this food (Table 2). The daily ration for 

 fish in group 2 was 2,238 cal/d and was 2,245 cal/d 

 for fish in group 3. 



standard techniques (Table 2). Laboratory fish 

 were used for all measurements except for the 

 caloric value of northern anchovy oil where sea- 

 caught specimens were used. 



SPAWNING FREQUENCY AND RATE 

 OF EGG MATURATION 



Number of Spawnings per "Vfear 



We plotted the fraction of females spawniing per 

 day ( females with 24-h-old postovulatory follicles ) 

 as a function of sampling date to estimate the 

 number of spawnings produced by female north- 

 ern anchovy in 1 yr. The seasonal change in the 

 fraction of females spawning followed the sea- 

 sonal change in the average relative larval abun- 

 dance for 1953-60 (Lasker and Smith 1977) (Figure 

 2). The fraction of females spawning was the 

 highest during peak spawning months and de- 

 clined to zero by September. In peak spawning 

 months the percentage of mature females spawn- 

 ing per day was 16-14% , indicating that individual 

 females spawned every 6-7 d. The seasonal decline 

 in the fraction of females spawning per day could 

 be caused by an increase in the interval between 

 spawnings in individual females, or by a complete 

 cessation of spawTiing by an increasingly larger 

 proportion of the population, or by a combination 

 of these events. 



Table 2. — Mean calories per gram dry weight of various 

 northern anchovy tissues and food. 



' 1 8% IS the mean fat content of northern anchovy ovaries: caloric value was 

 calculated from the values for fat and fat- free ovary. 



Dry weight and fat content of northern anchovy 

 were determined for the first and last samples of 

 groups 2 and 3. Fish were dried in an oven at 60° C 

 until constant weight and fat extracted using 

 Soxhlet extraction with chloroform-methanol 

 (Krvaric and Muzinic 1950). 



Caloric values of northern anchovy oil, newly 

 spawned eggs, ovaries and whole females ( without 

 ovaries), and Oregon Moist Trout Pellets were 

 estimated using a Parr bomb calorimeter and 



000 



Month 



Figure 2. — Fraction of mature northern anchovy females from 

 the Southern California Bight spawning per day during various 

 months (dots). Fraction calculated from incidence of females 

 with 24-h-old postovulatory follicles (Hunter and Goldberg 1980; 

 Hunter and Macewicz 19801. Triangles indicate relative larval 

 abundance per month from 1953 to 1960 I Lasker and Smith 

 1977). Shaded areas indicate months where spawning fraction 

 was not estimated; total spawnings per year by northern 

 anchovy females was estimated from areas under the two curves 

 (see text). 



218 



