FISHERY BULLETIN: VOL. 79. NO. 2 



that the Japanese anchovy, Engraulis japonicus, 

 fed Euphausia pacifica in the laboratory, had a 

 gross growth efficiency (in calories) of 11.9'7f, 

 which is similar to our estimate of 12.8% for 

 E. mordax. 



Energy Budget 



Growth of northern anchovy in the sea from age 

 1 to 2 yr is equivalent to a gain of 6.2 x 10^ cal, and 

 the energy cost of 20 spawnings for a 1-yr-old 

 female is about 10 x 10^ cal (documentation given 

 in Table 7). Assuming that the caloric conversion 

 efficiency for northern anchovy in the sea is the 

 same as in the laboratory ( 12.8%), 1-yr-old females 

 (mean weight 10.3 g) consume annually about 127 

 X 10^ cal of which 8% would be used for reproduc- 

 tion and 5% for growth. This implies a daily rate of 

 consumption in the sea of 348 cal/d, or, on a wet 

 weight basis, about 4% body wet weight/d in 

 copepods (copepods = 5,252 cal/g dry weight, 

 Laurence (1976); water content of Calanus = 

 84.7%, Lovegrove (1966) ). Sirotenko and Danilev- 

 skiy (1977) estimated from stomach content analy- 

 sis that the Black Sea anchovy, E. encrasicholus, 

 consumed 1.5-3.7% of their body weight/d; Mikh- 

 man and Tomanovich (1977) estimated from field 

 captured specimens that E. encrasicholus con- 

 sumed 1.4-3.0% of their body weight/d when they 

 fed upon phytoplankton, 3.4% when they ate 

 zooplankton, and 9.3% when they ate benthic 

 animals. Our estimate of 4-5% body weight/d for 

 females 1-3 yr old is within the range of these 

 values. 



DISCUSSION 



Spawning Frequency 



Northern anchovy females matured eggs in the 

 laboratory at the rate required for weekly spawn- 

 ing, thus supporting the conclusions of Hunter 

 and Goldberg (1980) and Hunter and Macewicz 



(1980). Our estimates of reproductive effort (egg 

 calories/ration calories) of 8-11% (Table 7) seem 

 reasonable, thereby supporting our estimate of 20 

 spawnings/female per year. Our calculations in- 

 dicate that this effort could be sustained by a daily 

 ration of natural foods of 4-5% of the fish wet 

 weight/d which is similar to the natural ration of 

 E. encrasicholus ( Sirotenko and Danilevskiy 1977; 

 Mikhman and Tomanovich 1977). Few estimates 

 of reproductive effort exist for fishes. Lasker 

 (1970) estimated that the cost of reproduction in 

 Pacific sardine, Sardinops sagax, was about 1% of 

 the total annual caloric requirement. He assumed 

 the caloric equivalent of the ovary is spawned per 

 year, which now seems an underestimate. Con- 

 stantz (1976) estimated that reproductive effort 

 ranged from 4 to 15% in two populations of 

 Poeciliopsis occidentalis. Hirshfield (1977) found 

 in laboratory studies that reproductive effort was 

 related in a complex fashion to temperature and 

 ration in medaka, Oryzias latipes; he estimated 

 reproductive effort ranged from 10 to 18% in two 

 natural Japanese populations. We conclude that 

 20 spawnings/3rr is a reasonable estimate of the 

 number of spawnings produced by females in the 

 northern anchovy central subpopulation. The fact 

 that two-thirds of the cost could be supported by 

 the average annual decline in fat stores supports 

 this conclusion. 



An implication of this study is that egg matura- 

 tion and vitellogenesis are continuous during 

 peak spawTiing months. Evidence for this includes: 

 the large fraction of the females in the population 

 spawning per day during peak spawning months 

 (10-16% ); the presence of the caloric equivalent of 

 only one or two spawning batches in the ovary at 

 any time; the inverse relation between the abun- 

 dance of egg sizes in the ovary and oocyte matura- 

 tion rate; and the continuation of egg maturation 

 until the last batch of eggs is spawned. Although 

 maturation and vitellogenesis probably continue 

 for extended periods, the rates probably vary. The 

 seasonal decline in the fraction of females in the 



Table 7. — Annual energy budget for female northern anchovy. 



Age (yr) 

 Beglnning-end 



SU (mm) 

 Beginning-end 



1-2 

 2-3 

 3-4 



93-112 

 112-126 

 126-136 



'From Spratt (1975). 



^From Equations (1) and (2) where 15.4% of dry weight = tat. 



^Gain in calories assuming 15.4''o of dry weight = fat; caloric values in Table 2. 



"Caloric content of 20 spawning batches; batch size calculated for mean female wet weight over the year (method illustrated in Table 4). 



^Reproduction calories -i- growth calories/0. 128. where 0.1 28 is growth conversion efficiency determined in laboratory (Table 6). 



226 



