YELLOW PERCH OF LAKE ERIE 



249 



completed, or nearly completed, growth for the 

 year. The continued growth, especially of the 

 age group just entering the commercial fishery in 

 large numbers (group II) can be expected to in- 

 crease the relative abundance of the j^ounger indi- 

 viduals among the legal-sized fish. The belief 

 that the time of capture in a year explains the 

 shift of dominance from group III to group II is 

 supported by the strikingly similar changes found 

 in the impouncUng-net data. 



If the data for impounding and gill nets are 

 considered together, it may be stated that the 

 fishery is supported chiefly by age groups II and 

 III. Age group III dominated the commercial 

 catch of gill nets in late summer of both 1927 and 

 1928. The same age group is in all probability 

 usually dominant in the earh-season catches also. 

 The late-season (late September to early Novem- 

 ember) commercial catches by gill nets were dom- 

 inated by age group II in 4 of the 6 years 1943^8. 

 Age group III dominated the late-season giU-net 

 catches only once (1947) and age groups II and 

 III were of equal abundance in 1945. The com- 

 mercial catch of impounding nets appeared to be 

 dominated by age group III in the spring and 

 during at least part of the summer. As growth 

 during the summer brings an increasing percent- 

 age of age group II to legal size this age group 

 assumed a more important position in the catch. 

 Dominance by age group II seems to be character- 

 istic of late-season impounding-net catches, al- 



though there may be exceptions, as in 1929 and 

 1945, when age group III may be the stronger. 



The dependence of the fishery on two age groups 

 renders the abundance of the Lake Erie perch 

 very sensitive to natural fluctuations in the 

 strength of year classes and vulnerable to over- 

 fishing. The small quantity of fish of commercial 

 size that is carried over from one year to the next 

 makes the maintenance of protective measures to 

 ensure an adequate stock of spawners at all times 

 highly imperative. 



The percentage representation of the year classes 

 in each year's collection of j^ellow perch from im- 

 pounding nets in Lake Erie is recorded in table 

 28. The data for the 1937 collection have been 

 omitted because of the long time interval separat- 

 ing this sample from the earUer collections. Dis- 

 cussion of the year-class composition of the 1937 

 samples will be based on the age-composition 

 data of table 21. No tabulation has been pre- 

 sented of the year-class composition of gill-net 

 samples because of the highly selective action of 

 that gear. 



The inability of impounding nets to retain repre- 

 sentative samples of the j'ounger age groups, and 

 the rapid rate at which year classes disappear from 

 the fishery owing to the short life span, combine 

 to make interpretation of data on the year-class 

 composition of the samples most dLSicult. Age 

 group (first year of life) is of course absent from 

 all collections, and normally group-I fish occur 



Table 28. — Occurrence of year classes of yellow perch in the catch of impounding nets of Lake Erie 



Asterisk designates dominant year class each year; roman numerals show age at capture] 



PART I-PERCENTAGE BASED ON ALL FISH TAKEN 



PART n— PERCENTAGE BASED ON COMMERCIAL CATCH 



