YELLOW PERCH OF LAKE ERIE 



233 



Table 14. — Calculated annual growth increments according 

 to calendar year and year of life of Lake Erie yellow perch 

 taken by impounding net, 1927-29 



[Data for sei.es shown separately] 



Year of life 



Males: 



Age group HI: 



Fourth year. 



Third year_- 



Second year. 



First year 



Age group II: 



Third year.- 



Second year. 



First year 



Females: 



Age group III: 



Fourth year. 



Third year.- 



Second year. 



First year 



Age group II: 



Third year. . 



Second year. 



First year 



Calculated growth Increments 

 (Inches) in— 



1924 



3.6 



3.7 



1926 



2.3 

 3.6 



3.6 



2.4 

 3.5 



1926 



1.9 

 2.6 

 3.8 



2.7 

 3.8 



1.9 

 2.7 

 3.8 



2.9 

 3.8 



1.2 

 1.9 

 2.9 



2.1 

 3.3 

 3.6 



1.2 

 2.3 

 3.0 



2.3 

 3.4 

 3.6 



1928 



0.9 

 1.8 



1.4 

 3.2 



1.0 

 2.0 



1.3 



3.2 



1.7 



0.9 



which the individual years belong. The analysis 

 has been confined to the growth of age groups II 

 and III since other age groups contained too few 

 fish to give reUable averages in all years. 



The calculated annual increments of age groups 

 II and III taken in 1927-29 are shown for each sex 

 in table 14 and those for the fish taken in 1943-48 

 are given in table 15. The data in both tables are 

 arranged so that the horizontal rows show the 

 growth in different calendar years of fish in the 

 same year of life. The vertical columns show the 

 growth in a single calendar year of fish in different 

 years of life. The growth histories of the individ- 

 ual age groups are shown in rows running diago- 

 nally from the bottom to the right. 



The method of estimating annual fluctuations 

 in growth may be illustrated by the 1925 and 1926 

 data for the females in table 14. The 1926 



Table 15. — Calculated annual growth increments according 

 to calendar year and year of life of Lake Erie yellow perch 

 taken by impounding net, 1943-48 



[Data for sexes combined] 



growths of 2.7, 3.8, and 3.8 inches of age group III 

 in the first and second years of life and of age 

 group II in the first j^ear of life totaled 10.3 inches 

 or 0.9 inch more than the total (9.4) of the corre- 

 sponding increments in 1925 (2.4, 3.5, and 3.5). 

 The average of the two totals is 9.85 inches. Com- 

 pared with this average, the total growths in 1926 

 showed an improvement of 9.1 percent. A con- 

 tinuation of this procedure shows the percentage 

 change in growth from each year to the next. The 

 position of each year's growth with respect to that 

 of 1924 is obtained by the successive addition of 

 the percentages of change. For example, the 

 growth of the group-Ill females decreased 5.6 

 percent from 1924 to 1925 as determined by this 

 method of computation, but as indicated above, 

 that of the group-II and group-Ill females in- 

 creased 9.1 percent from 1925 to 1926. Hence, the 

 growth in 1926 may be said to have been —5.64- 

 9.1, or 3.5 percent better than in 1924. In order 

 to make the percentage deviations describe the 

 changes with respect to average growth over the 

 period 1924-29, rather than only to growth in 

 1924, the mean of the deviations as computed by 

 the above procedure was subtracted from the in- 

 dividual deviation of each year. The same pro- 

 cedure was used to determine the annual fluctua- 

 tions in growth in 1940 to 1948 (table 15). The 

 method just described for obtaining the percentage 

 deviations from average growth is that employed 

 by Hile (1941) to determine the annual fluctua- 

 tions in growth of the Nebish I.rake (Wisconsin) 

 rock bass. 



The annual percentage deviations of the growth 

 of the Lake Erie perch from the 1924-29 and 1940- 

 48 means are shown in table 16 for the sexes sepa- 

 rately, where possible, and for the sexes combined. 

 Particularly noteworthy is the very close agree- 

 ment between the percentage deviations of the 

 sexes. The coefficient of correlation between the 

 annual deviations in the growth of the sexes has 

 the high value of 0.959. This close correlation 

 may be construed as a strong argument for the 

 refiability of the percentages in table 16 as true 

 measures of the annual fluctuations in growth. 



The annual variations in the growth of the Lake 

 Erie yeUow perch were fairly large. The ranges 

 for the percentages in the period 1924-29 were 

 23.2 percent for the females, 15.2 percent for the 

 males, and 18.3 percent for the sexes combined. 

 The range in the percentage variation of the sexes 



