392 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 33. — Annual increments of growth in length of female Saginaw Bay yellow perch, spawning-run collections 



of 1943-55 



(Each diagonal gives the growth history of an age group, belonging to the year class indicated by the year of lst-year growth and captured in the spring of the 

 calendar year following the one for which the last increment is given. Number of fish in sample of each age group in parentheses immediately below lst-year 

 increment] 



growth in 1944 was less than that of 1943. In 

 1948 and 1949 change of growth was irregular 

 for the different age groups. In 1949, growth of 

 all years of life of age group VI were higher 

 than that of 1948, whereas in age groups V, IV, 

 and III growth was less than that of 1948. Simi- 

 lar comparisons for the females can be made 

 from table 33. 



The comparison of growth increments in tables 

 32 and 33 is instructive but gives only a rough 

 quantitative picture of the changes that occurred. 

 Hile (1941) suggested the use of the actual per- 

 centage changes in growth to obtain more precise 

 data on growth fluctuations. This method has 

 been applied to several fish populations (Hasler 

 and Farner, 1942; Carlander 1945a and 1945b; 

 Van Oosten and Hile, 1949; Jobes 1952; Hile 

 1954) . Procedural details for estimating the per- 

 centage changes in growth are not discussed here 

 since a complete account was given by Hile 

 (1941). 



The percentage deviations of growth from 

 average for the first year and for later years of 

 life (tables 34 and 35) indicate dissimilar growth 

 fluctuations during the two periods. A like situ- 

 ation was noticed by Hile (1941) for the rock 

 bass and by Van Oosten (1929) for the Saginaw 

 Bay lake herring. In the Saginaw Bay walleye, 

 on the contrary, the fluctuations of growth in the 

 first and in the later years were closely similar 

 (Hile 1954). 



Fluctuation in first-year growth 



Although the range of percentage deviations 

 of first-year growth from the 1942-51 average 

 was much greater for females than for males, the 

 trends were similar (table 34). The coefficient 

 of correlation between the annual deviations of 

 the sexes was highly significant (r = 0.850). 

 Therefore, the unweighted means of the percent- 

 ages for the sexes (bottom row of table 34) can 



Table 34.— Percentage deviation of growth in length for the 1st year of life of Saginaw Bay yellow perch from the 



1942-51 average 



Percentage obtained by linear interpolation. 



