GRISWOLD and SMITH: LIFE HISTORY OF NINESPINE STICKLEBACK 



Table 7. — Percent growth completed at various dates of 

 the 1967 season for ninespine sticklebacks in the Apostle 

 Islands. 



species (Lee, 1912). In the Lake Superior study, 

 there appeared to be no significant disappear- 

 ance of faster growing individuals from the 

 length-frequency distributions (Figures 5 and 

 6). However, as will be shown below, there 

 does appear to be a sex-specific mortality asso- 

 ciated with spawning. Since faster growing 

 males tend to spawn at an earlier age, slower 

 growing males may be left in the population 



20 30 40 50 60 70 



TOTAL LENGTH 



80 



Figure 5. — Length-frequency histograms of station 2 

 sticklebacks expressed in millimeters. N equals number of 

 fish in sample. 



10 - 



10 



LLl 10 



_i 

 a. 

 S 

 < 



I- 

 o 



20 



^ 10 

 u 



(£ 

 Ui 



10 



APRIL 

 (N=I56) 



JUNE 

 (N=906) 



^^b= 



JULY 

 (N=792) 



AUGUST 

 (N=I768) 



'"  ^-' 



SEPTEMBER 

 ( N= 52) 



NOVEMBER 

 _ (N=258) 



DECEMBER 

 (N = 36l) 



20 



40 50 60 



TOTAL LENGTH 



80 



Figure 6. — Length-frequency histograms of station 3 

 sticklebacks expressed in millimeters. N equals number of 

 fish in sample. 



longer. This tendency does not explain the 

 presence of "Lee's phenomenon" among fe- 

 males, where it is most prevalent. Figures 5 

 and 6 demonstrate that young-of-the-year fish 

 were being sampled throughout the latter part 

 of each season. Therefore, it is possible that 

 biased sampling of precocious individuals in 

 the younger age-groups creates the appearance 

 that younger fish of both sexes are growing 

 more rapidly than older fish did at the same 

 age. To minimize these suspected biases in the 

 growth-rate calculations, back calculations for 

 each year class over successive collection years 

 were averaged as unweighted means. 



Growth was fairly stable from year to year 

 (Tables 5 and 6) with the exception of 1964. 

 No explanation for this poor growth year was 

 discovered. 



1045 



