378 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 14. — Length-frequency distribution of Saginaw Bay yellow perch from the spawning-run samples according to year of 



capture 



[Modes designated by asterisks! 



Many of the undersized fish are destroyed in 

 the sorting and handling. Jobes (1952) indicated 

 that 14 percent of illegal perch taken by trap 

 nets in Lake Erie were dead when the nets were 

 lifted. Van Oosten (1936) also concluded that 

 trap nets destroyed more small fish than did 

 other kinds of nets. 



The length-frequency distribution not only 

 varies from year to year but also in the different 

 seasons of the year (table 15). A distinct trend 



Table 15. — Length-frequency distribution of Saginaw Bay 

 yellow perch on different dates in 1955 



in the length -frequency distribution and average 

 size of yellow perch caught in 1955 (sexes com- 

 bined) can be seen. The average length dropped 

 from 7.7 inches on April 18 to 6.1 inches on 

 June 7. Then the length increased to 6.5 inches 

 in early summer (June 22) and 7.6 inches in the 

 fall (October 19). The October fish were still 



0.1 inch shorter than those of the April 18 sam- 

 ple. Over the April 18— October 19 period the 

 modal intervals ranged from 5.5-5.9 inches 

 (June 7) to 7.5-7.9 inches (October 19). 



The percentage of legal-sized yellow perch also 

 varied seasonally. On April 18 this percentage 

 was 35.6, but fishermen did not benefit from the 

 relatively high value because fishing for perch is 

 not allowed at that time (closed season, April 15— 

 May 10). The proportion of legal-sized perch 

 subsequently fell to barely 2 percent on May 18 

 and June 7 and less than 2 percent on June 22. 

 In the fall (October 19) the percentage increased 

 again to 20.0. This increase is due in some meas- 

 ure to the presence of a large number of females 

 that typically attain larger size than males. 



Length Distribution of Age Groups 



In the compilation of data on the length-fre- 

 quency distribution of the age groups (table 16), 

 fish of the same age and sex in all the spawning- 

 run samples were combined. Because of a cer- 

 tain amount of year-to-year variation in the 

 length distribution, these combinations increased 

 the range and dispersion for the individual age 

 groups. The data serve, nevertheless, to show 

 the general distribution and the range of length 

 over which fish of a particular age can be ex- 

 pected to vary. In well-represented age groups, 

 the range for the males varied from 4 inches in 

 age group III to 5y 2 inches in age group V. The 

 females had a slightly wider range of 4 inches 



