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OCT APR MAY JUN 



1976 1977 



JUL 



Figure 2.-Gonadosomatic index (gonad weight expressed as a 

 percentage of total weight) for Menidia menidia collected during 

 1976-77 in Essex Bay, MA. The horizontal lines represent means, 

 the vertical lines represent one standard deviation, and the sample 

 size is given above the datum for each collection. 



6-13 July and 100% on 26 July. Hence, the breeding 

 season in Essex Bay began sometime after 6 May 

 and was over by 26 July during 1977. 



The potential annual fecundity of M. menidia may 

 be represented by the total number of eggs (recruit- 

 ment + maturing ova) within females just prior to 

 the breeding season (i.e., 6 May), if additional im- 

 mature eggs are not continually added to the recruit- 

 ment pool as the spawning season progresses. If this 

 premise is true, then there should be a continuous 

 decline in recruitment fecundity and total fecundity 

 during the breeding season (although not necessarily 

 in batch fecundity). 



Comparison of fecundities between sample dates 

 was facilitated by the following observations. Total 

 number of eggs per female was linearly related to 

 ovary-free body weight (Fig. 3). Batch fecundity was 

 also a simple linear function of ovary-free body 

 weight (Fig. 4) and the rates of increase in batch 

 fecundity, recruitment fecundity, and total fecundity 

 with increase in female weight were generally 

 similar among sample dates (i.e., regression slopes 



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3456789 10 

 OVARY- FREE FEMALE WEIGHT(g) 



Figure 3. -Relation between total number of eggs (recruitment 

 plus mature) and ovary-free female body weight for Atlantic silver- 

 sides captured just prior to the beginning of the spawning season (ti 

 May 1977) in Essex Bay, MA. 



differed little, t-test, P > 0.05). Correspondingly, 

 relative batch fecundity, relative recruitment fecun- 

 dity, and relative total fecundity (relative fecundity 

 = no. eggs/g ovary-free body weight) were each in- 

 dependent of body weight in nearly all tests (linear 

 correlation, P > 0.05), suggesting that females of all 

 sizes allocated about the same proportion of energy 

 to reproduction. Hence, fecundity was adequately 

 described and compared between dates if expressed 

 as a proportion of ovary-free body weight, rather 

 than as a function of weight. 



Batch fecundity, recruitment fecundity, and total 

 fecundity (no. eggs/g ovary- free body weight) during 

 the spawning season are presented in Figure 5. 

 Three patterns are evident. First, total fecundity and 

 recruitment fecundity monotonically declined (Fig. 

 5 A, B). Total fecundity was 1,609 ± 126 (95% C.L.) 

 on 6 May and declined to 876 ± 177 by the second 

 week of July (Fig. 5A) while recruitment fecundity 

 was initially 1,430 ± 128 on 6 May and declined to 

 716 ± 164 in July (Fig. 5B). Second, batch fecundity 

 differed significantly between sample dates, being 

 maximal during the middle of the breeding season 

 (266 ± 34 and 267 ± 23 on 6 and 22 June, respective- 

 ly) and minimal at the beginning and end of the 

 breeding season (179 ± 21 and 181 ± 28 on 6 May 

 and 6-13 July, respectively; Fig. 5C). Third, many 

 recruitment eggs remained in ovaries near the end of 

 the spawning season (Fig. 5B) and most of these 

 were probably resorbed soon thereafter because all 

 females captured on 26 July contained only small (< 

 0.10 mm), transparent oocytes. Two females from 

 the 6-13 July collection contained only immature 

 eggs that appeared to be in a state of resorption and 

 had no maturing egg group. 



335 



