FISHERY BULLETIN: VOL. 71, NO. 4 



1) and for males for the 1963 through 1967 

 year classes (Table 2). Females averaged 47.5, 



61.6, 68.5, 74.3, and 80.0 mm in total length 

 at the first through fifth annuli, respectively. 

 Age-groups I, II, and III in males averaged 



46.7, 60.2, and 65.6 mm. There was little dif- 

 ference between growth rates of fish from sta- 

 tions 2 and 3. Females from station 2 were 

 longer at the end of 2 of 5 yr of life, and males 

 from station 2 were longer at the end of 2 of 3 

 yr of life. Females grew faster than males dur- 

 ing the first year, being 0.02 and 1.35 mm 

 longer at stations 2 and 3, respectively, at an- 

 nulus I. These differences increased to almost 

 3 mm after 3 yr. Females reached age 5, males 

 age 3. 



Both sexes showed the greatest growth in 

 length in their first year (Tables 5 and 6), when 

 females attained about 60% and males about 

 70% of maximum size. The average annual in- 

 crement calculated from the summation of 

 annual increments was about 30% for both 

 sexes during the second year and on the order 

 of 10% per annum thereafter. 



Annulus formation was evident in some 

 sticklebacks as early as June in 1967, and all 

 annulus formation was complete by the second 

 week in July. Annulus formation occurred be- 



fore spawning and started when surface water 

 temperatures reached about 10 °C in 1967 and 

 1968. 



PeiTentage of annual growth completed at 

 any date during the growing season was com- 

 puted by comparing the length at capture on a 

 given date in 1967, an average growth year as 

 indicated by average annual increments, with 

 the calculated length at annulus formation in 

 1968 (Table 7). Male growth was faster at the 

 beginning of the growing season with about 50% 

 of the annual growth being completed by late 

 July. Early seasonal growth of females was 

 slower than in males, and 50% of the annual 

 growth was not complete until mid-August. 

 Growth then declined and was complete or 

 nearly complete in all fish by early December 

 when fall turnover occurred. These calculations 

 are consistent with length-frequency distribu- 

 tions of fish from stations 2 and 3 (Figures 5 

 and 6). These monthly distributions show that 

 growth, as indicated by increasing modal length 

 of the two apparent age-classes, had begun by 

 July and continued into December. 



Older fish had a tendency to grow slower in 

 their first years of life than the younger fish 

 (Tables 1 and 2). This growth pattern (Lee's 

 phenomenon) has been reported for many fish 



Table 5. — Grand average increment in total length of female ninespine sticklebacks from stations 2 and 3 expressed 



in millimeters. 



Table 6. — Grand average increment in total length of male ninespine sticklebacks from stations 2 and 3 



expressed in millimeters. 



1044 



