YELLOW PERCH OF LAKE ERIE 



231 



T,\BLE 13. — Increment of growth completed by Lake Erie 

 yellow perch at certain dates in 1929 



' Includes flsh whose sex was not determined. 



full-season increments of growth.* Other com- 

 binations of collections, as for example, that of 

 the samples of July 17 and 23, 1928, were made 

 only after examination proved the combinations 

 to be warranted. 



The data of tables 11, 12, and 13 were presented 

 in considerable detail to bring out the fact that 

 neither sex nor age appeared to affect the course 

 of the season's growth. Females did not show 

 consistently lower or higher percentages than 

 males taken on the same day or days; neither did 

 the percentages vary consistently among samples 

 of different age groups captured on the same 



> Estimates of the progress of growth during the season of capture made 

 by Hile. for the Cisco (1936) and for the rock bass (1941) in the lakes of north- 

 eastern Wisconsin, were based on comparisons of the growth increments up 

 to the time of capture with the full-season growth as calculated from samples 

 of the same year class in collections of later years. The severe discrepancies 

 between the calculated growth histories of different age groups of the same 

 year class of the Lake Erie yellow perch prohibit the use of the same pro- 

 cedure in the present stuily. 



dates. It appears valid, therefore, to employ 

 the weighted percentages (given in each table) as 

 measures of the proportion of season's growth 

 completed at different dates. 



In order to obtain a more definite idea of the 

 course of growth through the season, the weighted 

 percentages of tables 11, 12, and 13 were plotted 

 as functions of time within the season (fig. 7). 

 The smooth curve appearing in figure 7 was fitted 

 by inspection to the percentages for 1928 and 1929. 

 For reasons to be brought out presently the single 

 percentage available for 1927 (that of growth up 

 to October 24) was held to represent exceptional 

 conditions and was disregarded in the fitting of 

 the curve. 



If the curve of figure 7 is accepted as descriptive 

 of the normal course of growth of the yellow 

 perch during the season, the following estimates 

 are obtained: 



Percent Percent 



_ , . r If total growth of total growth 



b or montn OI— end of month within month 



June 15 15 



July... 50 35 



August. 80 30 



September. 100 20 



According to these estimates relatively little 

 growth was completed before July 1 (only 15 per- 

 cent of the total) . The greatest increase in length 

 in a single month occurred in July (35 percent). 

 Growth dropped shghtly in August (to 30 percent) 

 and sharply in September (to 20 percent), and 

 appears to have ceased toward the end of Septem- 

 ber. The small percentage completed on July 1 

 suggests that growth began some time in Jime, 

 although it is not possible to be certain on that 

 point. 



The preceding description of the course of the 

 growth of the yellow perch during the season 

 must be recognized as merely an approximation 

 since it was based on rather limited and scattered 

 data. The data for 1927 indicate that with 

 exceptional conditions the percentage of total 

 growth completed at different times within the 

 growing season may vary considerably. Perch 

 collected on October 24, 1927, were found to have 

 completed only 88 percent of the estimated total 

 growth for the season. Although the indicated 

 growth of 12 percent of the season's total between 

 October 24 and October 31 does seem to be too 

 high, the data provide evidence, nevertheless, that 

 growth was proceeding actively in October. 



