FISHERY BULLETIN: VOL. 71, NO. ^ 



63 



65 



67 



69 71 73 75 



FISH LENGTH ( mm) 



Figure 8. — Least squares regression lines indicating the 

 relationship between fish length and number of eggs. 

 Solid line and dots, station 2; dashed line and open circles, 

 station 3. 



Mean weight of ovaries containing ripe eggs 

 was 10.2% and 9.8% of mean fish weight at 

 stations 2 and 3, respectively. Since ovaries 

 in immature fish are very small and some 

 somatic growth had already taken place by 

 spawning time, it is clear that gonad matura- 

 tion requires a gain in weight of over 10% of 

 the winter weight of the fish. However, early 

 somatic growth in mature females is consider- 

 ably less than in males (Table 7). It appears 

 that most early annual weight gain in females 

 goes into egg production and rapid somatic 

 growth does not occur until after spawning. 



Coefficient of determination (r^) values were 

 0.71 and 0.72 for stations 2 and 3 respectively. 



Differences in fecundity relationships be- 

 tween the two stations were implied and an- 

 alysis of covariance revealed a significant dif- 

 ference (0.01 level) in elevation of the two re- 

 gressions (^i28~ 19-0). With the presence of 

 atresia, the most obvious theory for this differ- 

 ence would be a slight difference in time of 

 spawning at the two stations. This is suggested 

 by the slightly smaller mean weights of female 

 fish from station 2 sticklebacks at the time of 

 these ovary collections (Table 14). This could 

 be interpreted to mean station 2 females had 

 not matured as much as station 3 fish since 

 female sticklebacks increase their weight by 

 as much as 10% during the maturation period. 

 Atresia would then have acted on the station 

 2 fish to reduce their fecundity. Any differ- 

 ence in spawning time is probably related to 

 environmental differences between the sta- 

 tions, exemplified by the presence of rooted 

 aquatics at station 3 and their apparent ab- 

 sence at station 2. 



Measurements of egg size of six P. pungi- 

 tiiis, 62-79 mm long, were made on eggs de- 

 posited in laboratory aquaria, since Vrat (1949) 

 found stickleback eggs reached maximum size 

 only on extrusion into the water. Eggs were 

 left in the water about 15 min before they 

 were removed and measured under a binocular 

 microscope equipped with an optical microm- 

 eter. Egg size appeared to be rather constant 

 with no relationship to size of fish. Egg diame- 

 ter ranged from 1.53 to 1.98 mm (x — 1.76 mm). 



Sex Ratio and Sex Specific Mortality 



The sex ratio of sticklebacks was determined 

 for various years of life and for various months 

 because it was obvious from general observa- 

 tion that females predominated in the samples. 

 All 808 fish from which otoliths were extracted 

 were used in the sex ratio calculations. The 

 ratios were: 



The X values for age-groups II and older 

 were significant at the 0.01 level, indicating 

 the ratios were significantly different from 1 

 to 1. 



The sex ratios by month of all fish 1 -I- and 

 older beginning in April were: 



Month 



April 



May 



June 



July 



August 



November 



December 



Male: Female 



0.692:1 

 .714:1 

 .366:1 

 .197:1 

 .211:1 

 .137:1 

 .100:1 



Monthly length-frequency histograms (Figures 

 5-6) indicate the presence of two distinct age- 

 groups in most months, the older fish being 

 strung out in an uneven pattern beyond the 



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