HUNTEK and ROE: THE SPAWNING ENERGETICS OF NORTHERN ANCHOVY 



The area under the curve for fraction of females 

 spawning per day is an estimate of the number of 

 spawnings produced per female from February to 

 September. This calculation indicated that each 

 mature female northern anchovy spawned on the 

 average 15 times between February and Septem- 

 ber. The number of spawnings that occurred in 

 October- January ( shaded area, Figure 2 ) had to be 

 estimated indirectly because no ovary samples 

 existed. We assumed that the number of spawn- 

 ings was proportional to the relative larval abun- 

 dance in October-January, adjusted by the ratio of 

 the areas under the spawning fraction and larval 

 abundance curves for Feburary to September. 

 This calculation indicated that about five spawn- 

 ings would have had to occur in October-January 

 to account for the abundance of larvae in that 

 period; this brings the total number of spawnings 

 for female to 20 for the ye£ir. 



0-1 0-2 0-3 04 0-5 0-6 0-7 08 0-9 

 MAJOR AXIS OF EGGS (mm) 



Form of Frequency Distribution of 

 Egg Size 



The form of the egg size distribution in mature 

 northern anchovy ovaries is illustrated for a 

 female taken 24 h after spawning and a mature 

 female without evidence of recent spawning ( non- 

 spawning) (Figure 3). Ovarian egg size distribu- 

 tions typically resemble these except for females 

 with hydrated eggs, where the hydrated eggs 

 stand out as a discontinuous group of large eggs. 

 In mature females (without hydrated eggs) the 

 egg size distributions are continuous and typically 

 have one or two modes as illustrated. In the 

 nonspawning female a major mode of large yolked 

 eggs existed between 0.6 and 0.8 mm (major egg 

 axis) and in the spawned female the first modal 

 group occurred at about 0.5 mm. Eggs <0.2 mm 

 are the most abundant size class in both ovaries. 

 These small eggs, also abundant in immature 

 ovaries, form part of the reservoir of immature 

 unyolked eggs which are matured during each 

 spawning season. 



Yolk appears in the egg when the major axis of 

 the egg reaches about 0.4 mm. The ovary of the 

 spawned female (20.2 g) in Figure 3 contained 

 9,384 yolked eggs, whereas that of the nonspawn- 

 ing female (25.3 g) contained 26,761 yolked eggs. 

 The batch fecundity equation (Equation (4) ) pre- 

 dicts a batch size of 9,110 eggs for the spawned 

 female and 13,120 eggs for the nonspawning fe- 

 male. Hence, about one spawning batch of yolked 

 eggs existed in the spawned female and about two 



Figure 3. — Total eggs in ovary i logm scale) as a function of the 

 major egg axis for a 20.2 g female northern anchovy i ovary-free 

 weight) captured 24 h after spawning and for a 25.3 g female, 

 showing no evidence of recent spawTiing i nonspawning). Small- 

 est eggs measured were 0.05 mm; measurements were made in 

 increments of 0.05 mm. Females were captured in January to 

 February 1979 in the Southern California Bight. 



in the nonspawning female. If a female were to 

 spawn more than a few times in one season, it 

 would have to mature and yolk many of the small 

 unyolked eggs in the ovary. If spawning were to 

 occur at weekly intervals for months, this would 

 be a continuous process. 



Rate of Egg Maturation Required for 



Continuous Production of Eggs Compared 



With Laboratory Maturation Rate 



For northern anchovy to continually mature 

 and add yolk to a series of egg batches, the 

 abundance of egg sizes in the ovary must vary 

 inversely with the rate of egg maturation. Thus, a 

 hypothetical curve for the rate of maturation of 

 anchovy eggs can be constructed from the average 

 size of eggs in each potential spawning batch 

 within an ovary, if the time between batches or 

 spawning frequency is known. This hypothetical 

 rate can then be compared with the rate of egg 

 maturation in the laboratory to determine if the 

 predicted rate is possible. 



To conduct this test for northern anchovy, we 

 partitioned the total number of eggs in the ovary 

 of 10 sea-caught fish into successive spawning 



219 



