406 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



a very brief period of time. For the yellow 

 perch Jobes (1952) and Pycha and Smith (1954) 

 agreed that the availability and kind of food 

 organisms had an important effect on the sur- 

 vival of newly hatched fish. 



Environmental Factors and Fluctuation in Growth 

 Rate 



In the attempt to uncover possible relations 

 between the four environmental factors and the 

 fluctuations of growth special emphasis was 

 placed on the environmental factors in the 

 months April to October. The months include 

 and probably exceed the growing season for 

 Saginaw Bay yellow perch. In samples collected 

 on June 7 and June 22, the percentages of indi- 

 viduals exhibiting new (current-season) growth 

 were 28.4 percent and 42.6 percent, respectively. 

 Jobes (1952) found that 15 percent of the total 

 growth of Lake Erie perch had taken place in 

 June. In the present study, although little or 

 no growth occurs before June, the months of 

 April and May were included because it is pos- 

 sible that the conditions in these two months 

 might have some influence on the growth of fish 

 later in the season. There are no good data on 

 the time the growing season ends in Saginaw 

 Bay but Jobes (1952) showed that in Lake Erie 

 growth appeared nearly to have ceased toward 

 the end of September (his 1927 data indicated 

 that growth was still active in October). Ac- 

 cordingly, to take into account any exceptional 

 growth later in the season, environmental condi- 

 tions in October were included in the present 

 study. 



As a matter of general procedure simple cor- 

 relations first were computed between annual 

 fluctuations in growth rate and each of the 4 

 environmental factors for each month in the 

 7-month period considered, and for certain arbi- 

 trarily selected combinations, a number of mul- 

 tiple correlations were computed to evaluate the 

 importance of combinations of the factors on 

 growth. 



First -year growth 



In view of repeated observations on the rela- 

 tion between population density and growth rate 

 (see preceding section on factors of change in 

 growth rate from the 1929-30 to the 1943-55 

 collections), it is logical to assume that first-year 

 growth may be good in years producing weak 



year classes and poor in years producing strong 

 year classes. The coefficient of correlation be- 

 tween the year-class strength and the fluctuation 

 in the first -year growth of Saginaw Bay yellow 

 perch for the years 1942-51 ran contrary to such 

 an assumption. The relatively high value of the 

 correlation coefficient (r — 0.507; r = 0.632 at 

 the 5-percent level) suggests that good growth 

 and a strong year class occur in the same calen- 

 dar year. 



The correlation coefficients of table 50 indicate 

 no correlation between the annual fluctuations in 

 growth rate and the fluctuations of different en- 

 vironmental factors except for turbidity in June 

 ' r = -0.799). The value was fairly high for 

 July also (r = -0.555) but was not significant. 

 Other values of r were very low except those for 

 rainfall in May (-0.617) and temperature in 

 October (0.565). The possible association be- 

 tween first-year growth and turbidity in June 

 and July was further indicated from the several 

 multiple correlations shown in table 51. Al- 

 though no multiple correlation involving tur- 

 bidity and 2 or 3 other factors was significant, 

 all that involved 1 other factor were significant 

 when turbidity in June (or June and July) was 

 included. The regression coefficients for turbidity 

 likewise were significant in three of these two- 

 factor equations. The only other indication of 

 significance lay in the regression coefficient for 

 precipitation in the combination: Temperature, 

 July and August; precipitation, May. The mul- 

 tiple correlation, however, was not significant. 

 Thus it appears that among the environmental 

 factors an argument can be made for turbidity 

 alone as possibly influencing first-year growth. 

 It is difficult to judge the effects of turbidity 

 on ecological conditions in Saginaw Bay or the 

 manner in which turbidity might affect the first- 

 year growth of yellow perch. The literature on 



Table 50 — Coefficients of correlation between annual fluc- 

 tuation of growth in the first year of life and temperature, 

 precipitation, water level, and turbidity 



[Asterisk Indicates significance at the 5-percent level. Absolute values for 

 r at 5- and 1-percent levels of significance are: 0.632 and 0..O5) 



