CLUTTER and THEILACKER: PELAGIC MYSID SHRIM' 



number roung : 4 9(body langth] - 14 5 

 numb*r vgo* : S.4[body Unglh) -16.0 . 



the time of extrusion of the eggs and the esti- 

 mated average age at which they were counted 

 (7 days) was estimated to be about 0.91. The 

 number of brood pouch young per female was 

 adjusted to the equivalent number of eggs ex- 

 truded per female by multiplying the number 

 of young by 1/0.91 = 1.10. The relationship 

 (Fig. 9) then becomes: number of eggs = 5.4 

 (body length, mm) - 16.0, which is shown in 

 Figure 9 as the upper, dashed line. 



We consider this to be a minimum estimate 

 of fecundity, because some females that had lost 

 eggs and larvae from the brood pouches during 

 collection and preservation were probably in- 

 cluded, despite our attempt to exclude them. 



Figure 9. — Relationship between body length and num- 

 ber of brood pouch young (eggs and larvae) of preserved 

 animals that were collected in the field. The lower line 

 (continuous) was fitted to the points by the method of 

 Bartlett (1949). The upper line (dashed) represents 

 the equivalent relationship for newly laid eggs, assuming 

 a brood pouch mortality of 0.013/day (see text). 



vae, the number of young per female is highly 

 variable. The average relationship between the 

 size of the female and the number of young, 

 calculated by the method of Bartlett (1949), is 

 represented by the straight line: number of 

 young = 4.9 (body length, mm) - 14.5. 



This estimate of fecundity is not quite cor- 

 rect because it was made from counts of eggs 

 and larvae that were a few days old. Some eggs 

 and larvae apparently are lost from the brood 

 pouch during the incubation period. Therefore, 

 we adjusted the relationship to account for the 

 mortality which occurs during the incubation 

 period. To estimate the mortality during incu- 

 bation, counts were made of the maturing ova 

 in the ovaries of 40 adult females and counts 

 were made of late stage larvae in the brood 

 pouches of 27 females of the same size, collected 

 at the same time. The ratio of mean number 

 of larvae/mean number of ova was 0.90. The 

 larvae were estimated to be 8 days old, giving 

 an instantaneous mortality rate of 0.013/day. 



The average age of the eggs and larvae from 

 the 310 preserved females (Fig. 9) was esti- 

 mated to be 7 days. Therefore, the relative sur- 

 vival of the young in the brood pouch between 



Maximum Estimate 



We observed that the females that had re- 

 leased young during the laboratory experiments 

 had a higher apparent fecundity than those that 

 were collected and preserved in the field. It is 

 possible that there was some bias in selecting 

 animals for the laboratory experiments, but we 

 were not aware of any. The number of young 

 released per female is plotted against the body 

 length of the female for those 17 specimens in 

 Figure 10. The average relationship between 



Figure 10. — Relationship between body length and num- 

 ber of young released by experimental animals in the 

 laboratory. The lower line (continuous) was fitted to 

 the points by the method of Bartlett (1949). The upper 

 line (dashed) represents the equivalent relationship 

 for newly laid eggs, assuming a brood pouch mortality 

 of 0.013/day (see text). 



101 



