100 



X 



o 



< 



s 

 o 



ci^ 10 

 to 



(S> 



O 



a: 



UJ 



m 



Z 



Z 



< 



LnY= 1601 LnX-4939 



r^ = 468 

 LnY= 2 340LnX-7 306 



^ I a-al \ — 1— l_L. 



10 100 



MEAN EGGS/m3 



1000 



Figure 2. — Mean density of northern anchovy eggs in the sea 

 and mean number of eggs in northern anchovy stomachs taken 

 in the Los Angeles Bight in March 1976 and 1977. Points are 

 means for 10 or more fish and means of 2-4 plankton tows. Upper 

 equation and the line is the geometric mean regression (Ricker 

 1973); lower equation is the predictive equation. 



actual density of eggs encountered by a school. 

 These measurements were derived from horizon- 

 tal tows made at the acoustically determined 

 depth of the school (15 m). Estimates from the two 

 tows taken in front of the school were 150 and 122 

 eggs/m^, whereas those from the two tows taken 

 behind the school were 75 and 54 eggs/m^. The 

 ratio of the means for these two sets (65:136) 

 indicated that 48% of the eggs in the water may 

 have been consumed by the school. Thus, a school 

 encountering a density of about 140 eggs/m^ may 



have consumed a large proportion of the eggs. The 

 density of eggs usually encountered by schools 

 during the peak spawning months may be in 

 excess of 140 eggs/m^ because the mean number of 

 eggs per stomach for fish in this school, 1.9 ±0.6 

 eggs (Collection 31, Table 1) was less than the 

 mean for all collections, 5.1. The typical density of 

 northern anchovy eggs within patches is not 

 known, but a value as high as 31,000 eggs/m^ has 

 been recorded (Hunter in press). 



The daily ration of eggs consumed by northern 

 anchovy was estimated from the equation, D = A 

 X B X C where Z) = ration (number of eggs), fi = 

 rate of gastric evacuation (0.701), A = mean 

 stomach contents, and C = duration of feeding 

 (24 h). This function has been used by Tyler (1970), 

 discussed and used by Eggers (1977), and criticized 

 and discussed by Elliott and Persson (1978). We 

 used for mean stomach contents (C), the mean of 

 the averages for day and night. Using the above 

 equation, the daily ration was 85.8 eggs/fish or 

 5.1eggs/gof fish(Table2). 



The simplest method for evaluating potential 

 effects of egg consumption is to calculate the 

 proportion of the nightly production of eggs con- 

 sumed by northern anchovy schools. Northern 

 anchovy produce 371 eggs/g of female per spawn- 

 ing and during peak breeding periods, about 16% 

 of the females spawn each night (Hunter and 

 Goldberg 1980). Thus each night, 0.16 x 371, or 

 59.4 eggs are spawned per gram of female in a 

 school. Assuming a sex ratio of 1:1, half this 

 amount, or 29.7 eggs, are produced per gram 

 school weight. The percentage of daily egg produc- 

 tion consumed by a school per day ( eggs consumed/ 

 eggs spawned) was 17.2% (Table 2). Smith (foot- 

 note 3) estimated the natural mortality of anchovy 



Table 2. — Number of anchovy eggs eaten, per day, proportion of egg production consumed, and the proportion 

 of natural egg mortality attributable to egg Ccinnibalism in northern anchovy. 



From the night samples. Table 1. 

 ^Hunter, J. R., and B. J. Macewicz. 1979. Sexual maturity, batch fecundity spawning frequency and temporal pattern of spawning 

 northern anchovy, Engraulis mordax, during the 1979 spawning season. Manuscript submitted for publication. 



814 



