FISHERY BULLETIN: VOL. 85, NO. 2 



Table 12. — Estimate of caloric input from copepods eaten by northern anchovy. 



'Hatching = Day 0. 



% = 3.06 e°°''. 



^W = 0.297 /^°^ 



'^r = c est/2.73 h (see text). 



^Estimated using equation in Table 3. 



^Average stomach contents calculated for f = >3 h; includes empty stomachs. 



'F^ = 1 2 r + c est. 



8% body weight eaten/d as copepods. 



^Calories/d, copepods; F x 4.9 cal/mg (Table 1). 



Gymnodinium cells, was available and the concen- 

 tration of large prey was varied. Availability of large 

 prey of a suitable size in the copepod diet was 10 

 times the number available in the low-density rotifer 

 diet. Because 4 mm (day 5) larvae fed copepods ate 

 mainly Gymnodinium, and those fed the low-density 

 rotifer diet ate mainly rotifers (Tables 2, 6), cope- 

 pods nauplii must be more difficult to catch than 

 rotifers, and consequently larvae consumed the 

 more abundant Gymnodinium cells. Larvae which 

 consume prey as they are encountered, rather than 

 choosing a diet that maximizes the energy gained 

 per unit foraging time, have been labelled "number 

 maximizers" as opposed to "energy maximizer" in 

 the parlance of Griffiths (1975) and Hughes (1979). 

 Additional evidence that points to northern anchovy 

 feeding as "number maximizers" is that, when prey 

 of the proper size were available, their feeding rates 

 paralleled prey abundance (Tables 10, 11). 



The energy budget I calculated for northern an- 

 chovy fed rotifers at two concentrations gives in- 

 formation on their growth requirements that can be 

 translated to growth requirements in the field. My 

 data support Boehlert and Yoklavich's (1984) and 

 Checkley's (1984) conclusions that larval fish may 

 exhibit a high growth rate or a high growth effi- 

 ciency, but not both at the same time. Boehlert and 

 Yoklavich studied Pacific herring, which are 2-4 

 times the weight of northern anchovy, but like an- 

 chovy feed continuously, and found that as consump- 

 tion increased, the total amount of food assimilated 

 continued to increase despite a decrease in the effi- 

 ciency of the assimilation. Checkley studied Atlan- 

 tic herring and found that the gross growth efficien- 

 cies of Atlantic herring increased with increasing 

 consumption, but he showed that the relation was 

 peaked, and by incorporating results from the 



literature for other species, he also described a 

 decrease in growth efficiency at high consumption 

 for larval fishes. 



ACKNOWLEDGMENTS 



I wish to thank Patricia Hadley Hansen for her 

 capable assistance during the laboratory phase of 

 this work, Bob Lucas for conducting the evacuation 

 experiments on nonfeeding larvae. Amy Kimball for 

 assisting with the data analysis, and Nancy C. H. 

 Lo for her consultation and valuable suggestions. 

 John Hunter, Pattie Schmitt, Ken Frank, Timothy 

 C. Lambert, and two anonymous referees critically 

 reviewed the manuscript and offered suggestions. 

 I appreciated the help of the manuscript support 

 staff, in particular Jean Michalski and Lorraine 

 Prescott. 



LITERATURE CITED 



Arthur, D. K. 



1976. Food and feeding of larvae of three fishes occurring 

 in the California Current, Sardinops sagax, Engraulis mor- 

 dax and Trachurus symmetricus. Fish. Bull., U.S. 74:517- 

 530. 

 Beyer, J. E. 



1980. Feeding success of clupeoid fish larvae and stochastic 

 thinking. Dana 1:65-91. 

 Blaxter, J. H. S., AND J. R. Hunter. 



1982. The biology of clupeoid fishes. Adv. Mar. Biol. 20:2- 

 223. 

 Boehlert, G. W., and M. M. Yoklavich. 



1984. Carbon assimilation as a function of ingestion rate in 

 larval Pacific herring, Clupea harengus pallasi. J. Exp. 

 Mar. Biol. Ecol. 79:251-262. 

 Brett, J. R., and T. D. D. Groves. 



1979. Physiological energetics. In W. S. Hoar and D. J. Ran- 

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226 



