YELLOW PERCH IN SAGINAW BAY 



413 



of apparent effects of turbidity on fluctuation of 

 growth were given. 



(26) Fluctuations in growth in the later years 

 of life were largely without trend. The maxi- 

 mum value (1948) was 16.8 percent above the 

 1944—54 average and the minimum (1952) was 

 16.2 percent below average. 



(27) Little or no evidence was discovered of 

 a correlation between growth in the second and 

 later years of life and: Commercial 'production; 

 abundance of legal-sized fish; temperature; pre- 

 cipitation; turbidity. Evidence was strong that 

 growth had fluctuated inversely with the water 

 level for May to October. No ecological explana- 

 tion could be offered as to how water level might 

 affect growth. 



(28) The calculated weights of the females 

 were higher than those of the males in all years 

 of life except the first year where the increments 

 were nearly equal. At the end of the second 

 year of life and in subsequent years, the females 

 were consistently heavier than the males. In the 

 sixth and seventh years of life the weights of the 

 females were nearly double those of males. 



(29) The annual increments of weight for both 

 sexes increased throughout life. The females at- 

 tained their greatest advantage in annual increase 

 over the males in the sixth year of life when 

 they added more than 2y 2 times the weight 

 gained by the males. 



(30) The annual fluctuations of growth in 

 weight were similar to those of growth in length 

 but covered a wider range. 



(31) The Saginaw Bay yellow perch collected 

 in 1943—55 had grown much more slowly than 

 fish collected from the Bay in 1929-30 and from 

 other Great Lakes waters. Possible factors of 

 the decrease in growth rate in Saginaw Bay were 

 discussed. It was concluded that the increase 

 in population density (about sevenfold or 

 greater) was probably the cause. 



(32) Male yellow perch in Saginaw Bay ma- 

 tured at a smaller size than females. Nearly all 

 the males were mature at the length of 5.0 to 

 7.5 inches. All males more than 7y 2 inches long 

 were mature. Among females 44 percent were 

 mature at 5.5-5.9 inches, 80 percent at 7.0-7.4 

 inches; 95 percent at 8.0-8.4 inches. All females 

 more than 9 inches long were mature. 



(33) The sex ratio of Saginaw Bay yellow 

 perch from the spawning runs in 1943—55 varied 

 widely from year to year. The percentage of 



males ranged from 26 percent in 1945 to 87 per- 

 cent in 1954. For all the collections combined 

 the males constituted 62 percent. The sex ratio 

 also varied seasonally (from 70 percent males on 

 April 18 to 30 percent on October 19 in the 1955 

 samples). 



(34) In 1929-30 the males grew scarcer with 

 increasing age whereas in most of the 1943—55 

 samples the percentage of males increased with 

 age. For the combined spawning-run collections 

 the percentage of males rose from 17 percent in 

 age group II to 77 percent in age group VI and 

 then dropped to 65 percent in the VII group. 

 The 4 older fish, however, were all females. The 

 fact that a rise in the percentage of males with 

 increase of age has been shown by other authors 

 for populations of stunted perch suggests that 

 the change in growth rate of Saginaw Bay yel- 

 low perch in recent years was also the cause of 

 this reversal in the changes of the sex ratio with 

 age. 



LITERATURE CITED 



Adams, Milton P. 



1937. Saginaw Valley report. Mich. Stream Control 

 Comm., 104 pp. 

 Allin, A. E. 



1929. Seining records and food of the intermediate 

 stages of Lake Erie fishes. Bull. Buffalo Soc. 

 Nat Sci., (1928), vol. 14, no. 3, pp. 188-194. 

 Alm, Gunnab. 



1946. Reasons for the occurrence of stunted fish popu- 

 lations with special regard to the perch. Medd. 

 Kungl. Lantbruksst. nr. 25, 146 S. 

 Beckman, William C. 



1941. Increased growth rate of rock bass, Ambloplites 

 rupestris (Rafinesque), following reduction in the 

 density of the population. Trans. Am. Fish. Soc, 

 vol. 70 (1940), pp. 143-148. 



1943. Further studies on the increased growth rate 

 of the rock bass, Ambloplites rupestris (Rafin- 

 esque), following the reduction in density of the 

 population. Trans. Am. Fish. Soc, vol. 72 (1942), 

 pp. 72-78. 



1950. Changes in growth rates of fishes following 

 reduction in population densities by winterkill. 

 Trans. Am. Fish. Soc, vol. 78 (1948), pp. 82-90. 

 Blegvad, H. 



1933. Plaice transplantations. Jour, du Cons., Cons. 

 Perm. Internat. Exp. Mer, vol. 8, pp. 161-180. 

 Gorley, J. O. 



1912. Report on the experimental transplantation of 

 plaice to the Dogger Bank carried out by the 

 Marines Biological Association in the years 1904-8. 

 Internat. Fish. Invest., Rep. 4 (Southern Area Cd. 

 6125), pp. 1-79. 



