FECUNDITl' OF THE PACIFIC SARDINE 



443 



the difference lies in the width of the perivitelline 

 space, wliich is nearly wanting in pre-cleavage 

 eggs taken during this period; such eggs averaged 

 only 1.20 mm. in diameter (range 1.02-1.38 mm.)." 



Measurements of the yolk diameters of 343 

 sardine eggs (fig. 2i) from 8 plankton samples 

 taken at various times and localities showed 

 the mean yolk diameter to be .84 mm. (range 

 .74-1.00). The mean egg diameter was 1.66 

 (range 1.40-1.90), indicating that this group of 

 eggs is comparable with those constituting Ahl- 

 strom's data (mean =1.70 mm.). One sardine of 

 those used for this study contained translucent 

 j-olked ovarian ova. The mean of 118 diameter 

 measurements of these ova was .84 mm. (range 

 .76-.96 mm.). As there was no perivitelline 

 space, these measurements are also yolk diameter 

 measurements. Clark's (1934) larger diameter 

 measurements of ovarian ova apparently include 

 a perivitelline space as well as the yolk and 

 therefore are not comparable with the ovarian 

 ova, .20 to .84 mm. (mean diameter), which 

 include yolk diameter only. Referring to sardines 

 containing translucent, yolked ovarian ova, Clark 

 (1934:11) states, "In the 11 years of study only 

 39 have been found among the thousands of 

 females which have passed under observation." 

 This would indicate that this stage is very transi- 

 tory. 



In table 13 I have summarized data on the 

 length of the spawning season off southern Cali- 

 fornia as determined from sardine egg surveys. 

 Between 70.7 and 97.2 percent of the spawning 

 in this area occurred within a period of two months, 

 and between 88.2 and 99.6 percent occurred 

 within a period of 3 months. The peak month 

 (italicized in table 13) was different in each year, 

 indicating the amount of variation that can 

 occur in the time of spawning. 



Clark (1934:19) bases the case for multiple 

 spawning in the sardine on four lines of evidence: 

 "The multiplicity of modes in the ova diameter 



Table 13. — Percent of spawning occurring in each month 

 of 1940 and 1941, 1950, and 1951 spawning seasons off 

 southern California ' 



' Based on sardine egg survey data given by Sette and Ahlstrom (1948) 

 and Ahlstrom (1954). 



frecjuency curves; the high degree of correlation 

 between the growth of these successive groups 

 of eggs; the occasional presence in the ovary of 

 a few ripe unspawned eggs accompanied by a 

 new ripening group; and the decrease, as the 

 breeding season advances, in the numerical ratio 

 between succeeding batches of eggs and the largest 

 size group . . ." 



The presence of different size-groups of yolked 

 ova in the developing ovaries of any species of 

 fish has been accepted by various authors as a, 

 if not the criterion of the existence of multiple 

 spawning in that species. However, it is also 

 known that in a number of species of fishes at 

 least some of the yolked ova of intermediate size 

 are not spawned, but instead degenerate and are 

 resorbed. This does not necessarily mean that 

 none of the intermediate-sized ova will be spawned. 

 Clark (1925) concluded that multiple spawning 

 occurred in the grunion {Leuresthes tenuis). The 

 ovaries of these fish contained a group of inter- 

 mediate-sized yolked ova from which a group 

 of ova to be spawned developed and segregated 

 by size at approximately two-week intervals. 

 At the end of the spawning season Clark (1925 : 22) 

 found that, "In all cases, eggs in the intermediate 

 group were undergoing a process of degeneration 

 and resorption." 



Hart and McHugh (1944) figure the distribution 

 of ovum diameters for three species of Osmeridae 

 found along the Pacific Coast of British Columbia. 

 As these three species participate in inshore runs 

 their spawning activities are much better known 

 than those of species that spawn offshore. 



One of these species, the eulachon {Thaleichthys. 

 pacijicus), migrates into rivers to spawn. The 

 spawning migration lasts from mid-March to 

 mid-May. Each female apparently spawns only 

 one batch of ova; the ovaries of a ripe female 

 contain only the group of matured ova to be 

 spawned and verv small ova that contain no 

 yolk. 



A similar condition is found in the Pacific 

 herring {Ciupea pallasi). I had the opportunity 

 to examine five ripe females of this species. I 

 found only one mode of yolked ova, all larger 

 than 1.00 mm. in diameter and the residual non- 

 yolked ova, all smaller than 0.20 mm. This 

 species is a demersal spawner, the eggs being 

 deposited on eel grass and seaweed. The spawn- 

 ing of the one group of matured ova may take 



