YELLOW PERCH IN SAGINAW BAY 



405 



1 New intake. 



Kecords of water level were taken from charts 

 and from monthly report sheets issued by United 

 States Lake Survey, Army Corps of Engineers. 



Environmental Factors and Fluctuation in Year-Class 

 Strength 



The first environmental factor checked as pos- 

 sibly having an effect on the strength of the year 

 classes was the density of the population. The 

 coefficients of correlation between the indexes of 

 abundance and production of Saginaw Bay yel- 

 low perch and the year-class strength for the 

 period 1939-52 had insignificant values (r = 

 0.321 and 0.272 for abundance and production, 

 respectively). This result indicates that the num- 

 ber of legal-sized fish did not affect the brood 

 strength. 



The correlation coefficients of table 48 also did 

 not indicate any significant relation between 

 year-class strength and the environmental fac- 

 tors. The coefficients for precipitation in April 

 (r = 0.462) and September (r = 0.492) although 

 moderately high, were far from significant. 

 Likewise the different multiple correlations 

 (table 49) failed to reveal any relation between 

 the year-class strength and environmental fac- 

 tors. No values of R 2 or of the regression coeffi- 

 cients were significant. Jobes (1952) similarly 

 failed to establish a relation between certain en- 



Table 48. — Coefficients of correlation between year-class 

 strength and temperature precipitation, water level, and 

 turbidity 



Table 49. — Coefficients in regression equation and R 2 in 

 the study of the relation between environmental factors 

 and year-class strength of Saginaw Bay yellow perch 



[When regression coefficient is not given, that variable was not considered 

 in the determination of the equation] 



Number of variables 

 and months 



4 variables: 



April-June. _ 

 May-June... 

 April-May.. 



May 



June 



3 variables: 



Various ' 



Various 2 



Various 3 



Various * 



2 variables: 



Various 5 



Various 6 



Various : 



Various 8 



April _. 



Various 9 



R°- 



0.060 

 .186 

 .064 

 .154 

 .476 



.323 

 .184 

 .093 

 .080 



.046 

 .004 

 .059 

 .010 

 .172 

 .183 



1 Temperature, 



2 Temperature, 

 1 Temperature, 



April-May. 



' Temperature, 

 April-May. 



 = Precipitation, 



6 Precipitation, 



7 Precipitation, 



8 Precipitation, 



9 Temperature, 



April; precipitation, June; water level, April. 

 April; precipitation, July; water level, April. 

 September-October; precipitation, June; water level, 



September-October; precipitation, July; water level, 



June; water level, April. 

 July; water level, April. 

 June; water level, April-May. 

 July; water level, April-May. 

 April; water level, April-May. 



vironmental factors and year-class strength of 

 Lake Erie yellow perch. 



Failure to establish a relation between the 

 year-class strength and the abundance of yellow 

 perch or any of four environmental factors is 

 not surprising. Unquestionably, we shall need 

 a much broader and more detailed knowledge of 

 limnological conditions within Saginaw Bay be- 

 fore we can hope for even a modest measure of 

 success. We need particularly to know condi- 

 tions during embryological development, at 

 hatching, and during the early larval stages. It 

 has long been believed that the strength of a 

 year class is determined very early in its history 

 (Hjort 1914), and many feel that the success of 

 reproduction is determined by conditions over 



