GRISWOLD and SMITH: LIFE HISTORY OF NINESPINE STICKLEBACK 



\ogW = - 4.5681 + 3.2190 log L 



where log W = common log of the weight (O.lg) 

 and log L = common log of the length (mm). 



Growth in weight was calculated on the basis 

 of weight at the time of each annulus formation 

 (Table 8). The greatest increment in weight 

 occurred in the second year of life for both sexes 

 at both stations. After the second year, growth 

 in weight declined rapidly, but the decline was 

 more pronounced in males. 



Instantaneous rates of growth in weight be- 

 tween consecutive ages varied from 0.804 to 

 0.223 for males and from 0.842 to 0.192 for fe- 

 males. 



may well be the explanation for this; however, 

 no historical records of stickleback abundance 

 in the Duluth area are available to help justify 

 this hypothesis. 



Temperature profiles were secured concur- 

 rently with trawl tows. Sticklebacks were found 

 in the warmer deep water in early spring, but 

 were evenly distributed at all depths during 

 spring turnover (Table 9). In midsummer they 

 congregated on the warm shallow snoals where 

 water temperatures reached as high as 20 °C. 

 When the fall turnover occurred in September, 

 they were again fairly evenly distributed at all 

 depths. By November the fish were beginning to 

 congregate in the deeper water and were found 

 there in great numbers during December. No 



Table 8. — Calculated weight attained by Apostle Islands sticklebacks at the time of annulus 



formation. 



DISTRIBUTION 



While some species of sticklebacks can be 

 found in a marine environment far from shore, 

 the ninespine stickleback is an inshore species 

 (Bigelow and Schroeder, 1953). Hubbs and 

 Lagler (1958) state that the species is abundant 

 in the Isle Royale and Keewenaw Bay areas of 

 Lake Superior. BCF operations found stickle- 

 backs in Nipigon Bay, on the north shore of the 

 lake. While sticklebacks were found throughout 

 the Apostle Islands, it should not be concluded 

 that these fish are similarly abundant on all 

 Lake Superior shorelines. Anderson (1969) re- 

 covered only 0.1 stickleback per trawl tow in 90 

 tows in the Duluth area, sampling during all 

 ice-free months. Degradation of water quality 



Table 9. — Average numbers of sticklebacks caught per 

 30-min trawl tow each month at various depths during 

 1967-69. 



[Numbers of tows are in parentheses.] 



data are available for midwinter, but it is 

 assumed the deepwater habitat is used at this 

 time since they were abundant there the fol- 

 lowing spring. Nelson (1968b) also noted sum- 



1047 



