YELLOW PERCH IN SAGINAW BAY 



407 



Table 51. — Coefficients in regression equation and R 2 in the 

 study of the relation between environmental factors and 

 growth in length in the first year of life of Saginaw Bay 

 yellow perch 



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

 the derivation of the equation. Values significant at the 5-percent level are 

 indicated by an asterisk] 



1 Temperature, October; precipitation, May; turbidity, June. 

 3 Temperature, June-August; precipitation, May-June; turbidity, June- 

 July. 

 3 Temperature, July-August; precipitation, May; turbidity, June. 

 * Precipitation, May; turbidity, June. 

 5 Precipitation, May; turbidity, June-July. 

 8 Temperature, June-August; turbidity, June. 



7 Temperature, October; turbidity, June. 



8 Temperature, July-August; turbidity, June. 



9 Temperature, October; precipitation, May. 



10 Temperature, July-August; precipitation, May. 



relations between turbidity and fish is volumi- 

 nous, controversial, and inconclusive. Arguments 

 have been particularly lively as to effects on fish 

 of turbidities at levels encountered in the Great 

 Lakes, especially Lake Erie. Langlois (1941) 

 held that siltation and turbidity resulting from 

 land erosion in the watershed were the cause of 

 the decreasing abundance of the more choice 

 species of fish in Lake Erie, and Doan (1942) 

 supported the same general view. Van Oosten 

 (1948), however, held the Langlois "turbidity 

 theory" to be invalid and offered extensive data 

 and detailed argument in support of his belief. 

 He pointed out in particular that: Recent trends 

 of turbidity in Lake Erie had been downward, 

 not upward as Langlois had argued; turbidity 

 levels encountered in Lake Erie and other Great 

 Lakes waters are too low to have a significant 

 effect on fish; no relation can be established for 

 Lake Erie species between annual fluctuations of 

 turbidity and of growth or year-class strength. 

 Van Oosten (1948) included an exhaustive review 

 of the literature on turbidity. 



If the observed negative correlation between 

 turbidity and the first-year growth of yellow 

 perch in Saginaw Bay is accepted as a cause- 

 and-effect relation, three possible explanations 



suggest themselves: The reduced light penetra- 

 tion may affect the photosynthetic action in 

 phytoplankton and thus lower the biological 

 productivity ; lowered visibility in the water may 

 impede the feeding activities of the small perch; 

 under turbid conditions the availability of food 

 may be lessened by the concentrations of zoo- 

 plankton near the surface (Doan 1942) while 

 perch remain near the bottom. 



Growth in later years of life 



The first approach to the study of factors 

 affecting growth beyond the first year was the 

 determination of correlations between the fluctu- 

 ation of growth and of abundance and produc- 

 tion of yellow perch in the same year (p. 368). 

 Both values of the coefficient were insignificant 

 (r = 0.049 and 0.112 for abundance and pro- 

 duction, respectively). This result indicates that 

 growth was not affected by fluctuations in the 

 numbers of legal-sized fish within the range of 

 variation of the stock during the present study. 



The coefficient (r) of table 52 show no corre- 

 lation between the annual fluctuation in growth 

 rate and the different environmental factors in 

 single months except for water level. The co- 

 efficients for water level were negative and sig- 

 nificant for May to October, but insignificant for 

 April. It is to be noticed also that the values of 

 r had an upward trend during the season. Other 

 moderately high but insignificant correlation co- 

 efficients were those for turbidity in April (r = 

 0.405), May (r = 0.555), and October (r = 

 —0.429) and temperature in June (r = —0.498). 



Table 52. — Coefficients of correlation between annual fluc- 

 tuation of growth in the second and later years of life and 

 temperature, precipitation, water level, and turbidity 



[Asterisk indicates significance at the 5-percent level. Absolute value for r 

 for turbidity at 5- and 1-percent levels of significance are 0.666 and 0.798; 

 for temperature, precipitation, and water level they are 0.602 and 0.735] 



The possible relation between growth in the 

 second and later years of life and water level 

 was further revealed from the selected multiple 

 correlations in table 53. When all the variables 

 were included in the regression equation, only 



