YELLOW PERCH IN SAGINAW BAY 



393 



describe the fluctuations in first -year growth very 

 satisfactorily. 



The poorest first -year growth (9.2 percent be- 

 low average) was made in 1942 (fig. 14). In 

 subsequent years a strong trend toward improve- 

 ment of growth is apparent. The first-year 

 growth in length remained below average until 

 1946. From 1946 to 1951 growth was continu- 

 ally above average reaching the maximum of 8.8 

 percent in 1951. 



Fluctuation of growth in later years of life 



The data used in the analysis of fluctuations 

 of growth of later years of life covered the 1944— 

 54 period only. The records for earlier calendar 

 years, particularly those for females, are believed 

 to be inadequate. In the later years of life, as 

 with first-year growth, the annual percentage 

 deviations of sexes (table 35) agreed very well 

 (coefficient of correlation, 0.942) and thus the 

 average percentage was used to describe the fluc- 

 tuation of growth. Data for the two periods 

 agreed further in showing a greater range of 

 fluctuations in the females. 



Contrary to the first-year growth which exhib- 

 ited a consistent trend, fluctuations in growth in 

 the later years of life were largely without trend, 

 indeed were almost erratic (fig. 15). Growth in 



years later than the first was slightly below 

 average in 1944 (—1.4 percent). Growth im- 

 proved to 2.2 percent above average in 1945 and 

 8.2 percent above in 1946, dropped to 4.2 percent 

 below average in 1947, and then jumped to the 

 11-year maximum of 16.8 in 1948. Following 

 a drop in 1949 (to 0.3) and an increase in 1950 

 (12.4, second highest value) 2 sharp decreases 

 carried the percentage to the 11-year minimum 

 (-16.2) in 1952. Growth improved in 1953 

 (—8.4 percent) but 1954 was the second poorest 

 year of the period (—14.0 percent). 



The difference in growth fluctuations between 

 the first year of life and those for later years 

 was discussed by past investigators. Van Oosten 

 (1929) showed that lake herring in their first 

 year of life spend a larger part of the growing 

 season inside Saginaw Bay than do older fishes 

 (which seem to move into Lake Huron) and thus 

 are affected more by any changes that might 

 happen in the Bay. Hile (1941) explained this 

 difference in the Nebish Lake rock bass on the 

 basis that conditions controlling the first year of 

 growth and that of later years are not the same. 

 In the Saginaw Bay perch, the factors that de- 

 termine first-year and later growth obviously are 

 dissimilar. In 1948, for example, first-year 

 growth was only slightly above average (4.0 per- 



1942 



1943 1944 



1945 



1946 1947 

 YEAR 



1948 



1949 



1950 1951 



Figure 14. — Annual fluctuations in the growth in length of Saginaw Hay yellow perch in the first year of life. 

 Males, broken line; females, solid line: both sexes, dots and dashes. 



Table 35. — Percentage deviation of the growth in lengths in the 2d and later years of life of Saginaw Bay yellow 



perch from the 1944-54 average 



