234 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 16. — Deviations in growth rate of Lake Erie yellow perch and in mean air temperatures at Sandusky, Ohio, from 



19S4-S9 and 1940-48 averages 



combined during the 1940-48 period was 17.1 or a 

 little less than in the 1924-29 period. Growth was 

 below average in 1924 but unproved each year 

 untU the maximiun was reached in 1927. The 

 sharp decline in 1928 was followed by an improve- 

 ment in 1929. Growth in 1940 was below the 

 average for the period 1940-48. The increase in 

 1941 was followed by a 3-year period in which the 

 growth fluctuated but little; the variations were 

 greater in 1945-48. The poorest growth in the 

 1940-48 period was in 1947 and the best in 1948. 



Neither a detailed discussion of all the probable 

 factors that contributed to the annual fluctuations 

 observed in the growth of the Lake Erie yellow 

 perch nor a review of the literature on fluctuations 

 in the growth of fish seems desirable. It may be 

 stated, however, that chief among the factors that 

 previous investigators found associated with 

 annual fluctuations in growth rate were changes in 

 the density of the population and fluctuations in 

 weather conditions (temperature and precipi- 

 tation) .' 



It is not possible to state definitely whether fluc- 

 tuations in the density of the yellow-perch popula- 

 tion affected the growth of the species in Lake Erie. 

 Three years in which growth was above average 

 (1926, 1927, and 1929) and a year of poor growth 

 (1928) occurred when members of the strong year 

 class of 1926 were abundant. This situation sug- 

 gests that fluctuations in the density of the popu- 

 lation may have little or no effect on the growth 

 rate of the Lake Erie perch. 



• Hile (1936) and Van Oosten (1944) have reviewed the literature on the 

 causes of fluctuations in the growth rate of fish. 



In the study of the relation between meteor- 

 ological conditions and the growth rate of the Lake 

 Erie yellow perch, detailed records of rainfall, the 

 percentage of possible sunshine, mean wind veloc- 

 ity, and temperature were consulted. Preliminary 

 analyses of the data demonstrated that no corre- 

 lation existed between growth rate and the first 

 three of the meteorological factors. Seemingly, 

 variations in the amount of sunshine did not affect 

 the production of food sufficiently to influence the 

 growth of the perch . The influence of rainfall which 

 would affect turbidity and the chemical content of 

 the water, and of variation in wind velocity which 

 would affect turbidity, appeared to be too small to 

 detect, or was obscured by other factors. 



Investigation of the relation between annual 

 fluctuations in temperature and in the growth rate 

 of the Lake Erie yellow perch yielded suggestive 

 results. The annual deviations of the air temper- 

 atures at Sandusky, Ohio,'" from the 1924-29 and 

 1940^8 averages in each month from May to 

 October, and the coefficients of correlation between 

 the annual deviations of growth and of temperature 

 in each month are shown in table 16. Included in 

 the table are data not only for the four months, 

 June through September, that were held to consti- 

 tute the normal growing season (p. 231), but also 

 for May and October. Evidence was brought out 

 that under exceptional conditions growth may 

 continue through October (p. 230), and it is be- 

 lieved possible that temperatures in May can 



" These data on air temperatures were taken from Climatologioal Data of 

 the United States by Sections, Weather Bureau, U. S. Department of 

 Agriculture. 



