YELLOW PERCH OF LAKE ERIE 



243 



increase in the later years of the 1944-48 period. 

 The average total length of the legal-sized group-II 

 yellow perch was considerably larger in each year 

 except 1945, of the period 1944^8, than in any 

 year of the period 1927-29. 



The totals for the two periods place the modal 

 length of the legal-sized fish in the 8.50 to 8.75 

 inch interval in 1927-29 and in the 9.00 to 9.25 

 inch interval in 1944-48. The weighted-average 

 total lengths for the two periods were 8.94 and 

 9.36 inclies, respectivelj*. The use of unweighted 

 means of the annual average total lengths to elim- 

 inate the distorting effects of the differences in 

 size of samples changes the averages for the 

 periods only slightly, to 8.96 and 9.32 inches. 

 Both methods of computation show that the 

 age-group-II fish of legal size taken in 1944-48 

 averaged about 0.4 inch longer than those taken 

 in 1927-29. 



The general pattern of the length distribution of 

 the legal-sized yellow perch assigned to age group 

 III failed to show as great differences between the 



1927-29 and 1944-48 periods as were exhibited 

 by group-II fish. The modal frequency interval 

 was well above the SJs-inch size limit in all years. 

 The average total length was greater each year 

 in the 1944-48 period than in either 1927 or 1928 

 l)ut agreed rather well with that of 1929. The 

 weighted-average length was almost identical in 

 both periods because the best represented year in 

 the earlier period included fish with the longest 

 average length while the best represented of the 

 later years included specimens with the shortest 

 average for the period. The unweighted means of 

 the annual averages in the two periods were 9.46 

 and 9.64 inches. The more reliable vmweighted 

 means thus show the legal-size 3-ellow perch as- 

 signed to age group III to have averaged approxi- 

 mately 0.2 mch longer ua 1944^8 than m 1927-29. 

 Although these data do not constitute proof, 

 the,v do offer strong evidence that yellow perch 

 in Lake Erie were growing at a faster rate in 

 1944-48 than m 1927-29. 



AGE COMPOSITION AND ABUNDANCE OF YEAR CLASSES 



In the study of the age and 3-ear-class composi- 

 tion of the Lake Erie yellow perch it should be 

 remembered that the samples must be considered 

 truly descriptive, not of the stock, but rather of 

 the catch of commercial gear. Trap-net and 

 poimd-net collections were employed in the bio- 

 logical study of the relative abimdance of age 

 groups and year classes because those nets are less 

 selective than gill nets. Although samples from 

 impounding nets in a single j^ear may not give 

 dependable information as to the relative abun- 

 dance of the year classes represented, the per- 

 sistent abundance or scarcity of a year class at 

 different ages, that is, in different years' collec- 

 tions, offers a reasonably trustworthy method for 

 the detection of exceptionally strong or weak year 

 classes. Of course, a knowledge of the age com- 

 position in both gill nets and impounding nets is 

 of importance in the practical problem of deter- 

 mining the effects of these types of gear on the 

 stock. 



The number of specimens and the percentage 

 occurrence of each age group in the yearly collec- 

 tions of biological samples from impounding nets 

 for the years 1927-37 are shown in table 21. Ago 

 group I dominated the samples in one (1927) of 



the six years in which collections were made, 

 although the percentage of abundance of this age 

 group was also high in 1937. Age group II 

 dommated in tlu-ce years (1928, 1930, and 1937), 

 and gi'oup III was dominant m the remaining two 

 years (1929 and 1932). However, the fact that 

 the 1932 samples were taken from the spawning 

 run in April, when the fish were comparable in 

 size and maturity to those in the next younger 

 age group iu the previous fall, throws doubt on the 

 validity of comparisons between the data for this 

 and other years. The spawning run consists al- 

 most entirely of matiu-e individuals; consequently, 

 those age groups containing high percentages of 

 immatm-e fish were not represented adequately in 

 the 1932 collections. The 1932 data serve, how- 

 ever, to show the age composition of the catch in 

 the spawning-run fishery. 



It will be brought out later (p. 251) that unusual 

 conditions made possible the dominance of age 

 group I in 1927 and of age group III in 1929. 

 Dominance of age group II in the late-season 

 catch of yellow perch in impounding nets may be 

 considered the normal condition. 



The preceding remarks were based on the total 

 catch of impounding nets including both legal- 



