250 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



only in small numbers. Age group II is affected 

 less by the selective action of the gear although 

 many fish of this age seem to be too small to be 

 retained in the nets in spring and early summer 

 (p. 221). It appears, then, that estimates of the 

 relative abundance of the year classes of the Lake 

 Erie perch must be based chiefly on the represen- 

 tation of the older fish in the different years' 

 samples. The relative strength of age group II 

 may be considered significant only if the sample 

 was taken late in the season. The scarcity of 

 group-I fish cannot be held to indicate a weak 

 year class, although a great abundance of yellow 

 perch of this age may be considered evidence of 

 a strong one. 



Ordinarily the estimate of the strength of a year 

 class is based on a knowledge of its relative 

 abundance in the collections of several successive 

 years. In the Lake Erie yellow perch, however, 

 the great scarcity of all fish older than age group 

 III, together with the unrehability of data on the 

 abundance of the younger age groups, makes the 

 application of this method very difficult. Further 

 complications arise from the failure to obtain 

 data in 1938 and 1939, and the fact that only the 

 legal-sized fish were sampled in 1943-48. 



Because of the limitations just outlined it is 

 not possible to make a precise arrangement of the 

 year classes of the Lake Erie yellow perch in the 

 order of their abundance. In fact it is possible 

 to speak with certainty concerning only one of 

 them — the year class of 1926. This year class 

 was without doubt one of exceptional strength. 

 It dominated the impoimding-net collections of 

 three successive years, 1927, 1928, and 1929. 

 Dominance of this year class as group I and as 

 group III is particidarly significant. The only 

 dominant group I of the collections occurred in 

 the 1927 samples. In the remaining collections, 

 age group I made up no more than 7.2 percent of 

 the samples except in 1937 and 1943. Age group 

 III was dominant in the late-season collections of 

 both 1929 and 1945. It should be pointed out 

 further than in 1928 the 1926 year class provided 

 relatively the strongest group II in any of the 

 collections (90.6 percent of the total). 



Three other year classes appeared to have been 

 of more than ordinary strength. The 1936 year 

 class as grouji I made up 47.3 percent of the entne 

 1937 sample (table 21). The only other collec- 

 tion with such an abundance of group-I fish was 



made in 1927 when the 1926 year class dominated 

 the catch of impounding nets. Unfortunately, no 

 samples were obtained in either 1938 or 1939 and, 

 as a consequence, nothing is known of the strength 

 of the 1936 year class at the ages when they would 

 contribute most to the fishery. However, produc- 

 tion increased from 3,305,000 pounds in 1936 to 

 7,782,000 pounds in 1938 when the 1936 year class 

 would have entered the commercial fishery in 

 greatest numbers. A large increase in yield is to 

 be expected when a strong year class enters the 

 fishery, and the 236-percent increase from 1936 to 

 1938 in the catch of yellow perch may be taken as 

 evidence, if not proof, that the 1936 year class was 

 of more than ordinary strength. The sharp decline 

 to 3,015,000 pounds in 1939 in the take of yeUow 

 perch could mean the exhaustion of an abundant 

 year class by an intense fishery. 



Despite the fact that the evaluation of the 

 strength of year classes in the 1943-48 period is 

 handicapped by lack of knowledge of the abun- 

 dance of group-I fish in those years, itseems evident 

 that the 1942 year class was one of considerable 

 size. It comprised 21 .4 percent of the 1943 samples 

 as age group I. The same year class was strongly 

 dominant as group-II fish in 1944 (85.2 percent) 

 and continued to dominate the commercial samples 

 as age group III in 1945 (55.6 percent). The 

 strong representation of the 1942 year class as 

 group-I fish in the commercial yield in 1943 and 

 the dominance of the group in the two succeeding 

 years could have been accomplished only by re- 

 markably good survival. 



Evidence, less convincing but nevertheless 

 strongly suggestive, points to 1944 as having pro- 

 duced a year class that was stronger than that 

 of either 1943 or 1945. The 1944 year class as 

 group-II fish made up 72.3 percent of the 1946 

 commercial samples and contributed heavily (41.9 

 percent) to the 1947 take when they were in age 

 group III. 



The 1943-48 data from gill nets (table 27) 

 provide some evidence of the relative strength of 

 year classes despite the fact that these nets are 

 highly selective and the samples were taken from 

 the legal-sized yellow perch. Age group III made 

 up 47.3 percent of the legal-sized fish in 1945 and 

 equaled the abundance of group II. This high 

 relative abundance of age group III supports the 

 conclusion reached from the trap-net data that 

 the 1942 year class was of more than ordinary 



