YELLOW PERCH OF LAKE ERIE 



235 



affect the time at which the season's growth begins. 

 It is recognized that air temperatures do not 

 provide an exact measure of water temperatures, 

 but air temperatures averaging exceptionally high 

 or low over the period of a month probably have a 

 significant effect on the average water temper- 

 atures, especially in such shallow water as in 

 western Lake Erie. Doan (1942) concluded that 

 either air or water temperatures may be used to 

 indicate monthly variations from normal, as 

 the two fluctuate similarly. 



Of the six coefficients of correlation between 

 annual fluctuations in growth rate and in the air 

 temperatures of individual months listed in table 

 16, only that for August (r=— 0.605) may be 

 termed "significant" (r= ±0.514 when p = 0.05). 

 The coefficient for September (r=0.504) fell just 

 short of the significant value and those for July 

 (r=0.347) and May (r = 0.346), though moder- 

 ately high were far from significant. The ex- 

 tremely low values for October (r= — 0.117) and 

 June (7-=— 0.030) offer not the slightest sugges- 

 tion of any correlation between annual fluctua- 

 tions in growth rate and temperatures in those 

 months. 



Even if temperature were known to be a major 

 factor in the determination of annual fluctuations 

 in growth rate, high correlations between growth 

 and temperature in individual months could 

 hardly be anticipated, since, as has been demon- 

 strated previously, the growing season of the Lake 

 Erie perch includes aU or part of several months. 

 It was with this in mind that the following coeffi- 

 cients of correlation (r) were computed between 

 annual fluctuations in growth and the combined 

 temperatures for several groupings of months: 



May to October (inclusive) —0. 124 



June to September (inclu.si ve) . 036 



May and June .218 



May, June, and July . 268 



May, June, and September . 416 



May, June, and October . 104 



May, June, September, and October . 352 



May and July . 371 



May, July, and September . 562 



May and September . 550 



May and October . ne 



May, September, and October . 327 



June, July, and August —.289 



June and August — . 461 



June, August, and October.. —.537 



June and September . 328 



June and October — . 176 



June, September, and October. 



July and August 



July, August, and September.. 



July and September 



August and October 



September and October 



.202 

 .384 

 .289 

 .651 

 420 

 180 



A detailed discussion is unnecessary, but 

 attention is called to the foUowing points: 



1. There is no evidence of correlation between 

 annual fluctuations in growth rate and in tempera- 

 ture during the season as a whole. The coeffi- 

 cients for the 6- and 4-month periods May-October 

 and June-September were both low (—0.124 and 

 0.036). 



2. Combinations of data for the 3 months, 

 May, July, and September, which exhibited 

 positive though statistically insignificant correla- 

 tions of temperature and growth yielded evidence 

 that a real correlation may exist. The coefficient 

 for the tliree months combined was 0.562, and 

 both of the groupings of two that included Septem- 

 ber — May and September (r= 0.550), and July 

 and September (7-=0.651)— also showed significant 

 positive correlation between temperature and 

 growth. Only the coefficient for May and July 

 (r=0.371) was below the significant value. It is 

 to be noted also that the combinations of still 

 other months with any of these three, or groupings 

 of them, diminished the correlation below the 

 significant level. 



3. The negative coefficient of correlation between 

 annual fluctuations in growth and the combined 

 temperatures during the three months, June, 

 August, and October, that exhibited negative 

 values individually was significant (r=— 0.537) 

 but was less than the figure for August alone 

 ('■=—0.605). Furthermore, not one of the co- 

 efficients for the three pairings of these months — • 

 June and August (r=0.461), June and October 

 (r=— 0.176), and August and October (r= 

 — 0.420)— was sigiuficant. This behavior of the 

 data suggests that any true negative correlation 

 between growth and temperature during the 

 growing seasons probably holds for August alone. 



Inasmuch as earUer investigations have demon- 

 strated that correlations among meteorological 

 factors themselves can obscure true relations be- 

 tween those factors and growth (Hile 1941) or even 

 render the data highly ambiguous (Van Oosten 

 and Hile 1949), the possibility of similar inter- 

 ference was checked in the present data. This 



