of abundance since quantities that could not be 

 sold were not reported. Data for walleyes and 

 perch are more reliable than those for the 

 other species. 



The catch per lift of all species combined 

 was only 70 percent of average in 1930. The 

 abundance of fish improved in 1931, and was 29 

 percent above the 9-year average in 1932. 

 Abundance declined during the next 3 years, 

 reaching the 9-year minimum of 67 percent in 

 1935. A slight increase in abundance in 1936 

 was followed by a sharp upturn to 133 percent 

 in 1937 and further, though less pronounced, im- 

 provement in 1938 to the 9 -year maximum (149 

 percent). The catch per lift of all fish combined 

 in both 1937 and 1938 exceeded that in any year 

 of the period 1930-1936. 



As might be expected, the annual fluctua- 

 tions in the abundance percentages of walleyes 

 resembled the fluctuation s for all species com- 

 bined. The directions of change were the same 

 in all years except 1936 when the abundance of 

 all fish combined improved (from 67 in 1935 to 

 72 in 1936) while that of walleyes declined (from 

 52 in 1935 to 43 in 1936). Measured in terms of 

 the average catch per lift the abundance of wall- 

 eyes was greatest in 1938 (149 percent of aver- 

 age) and was above average in 1931-1933 and in 

 1937. Walleyes were least abundant in 1936 

 (43 percent of average) and were below "normal" 

 in 1930 and 1934-1936. The rapid changes in 

 the abundance of walleyes in certain years are 

 especially striking. As an outstanding example 

 the 1937 abundance was 2.9 times that of 1936, 

 and the years of greatest and least abundance 

 (1938 and 1936) were separated by a single in- 

 tervening year. 



Fluctuations in catch per left of yellow 

 perch resembled those of all fish combined and 

 of the walleye . Examination of the data with 

 respect to the occurrence of "above-normal" 

 and "below -normal" years reveals complete 

 agreement between the perch and all species 

 combined and agreement between the perch and 

 the walleye in every year except 1931 (perch be- 

 low average and walleye above average) . The 

 directions of change in the abundance of perch 

 and walleyes were the same in every year but 

 1938 (a slight decrease in the abundance of perch 

 and an increase in the abundance of walleyes). 



It was concluded that trends in the fluctuations 

 in abundance of yellow perch and walleyes were 

 closely similar in the period 1930-1938, although 

 the actual values of the abundance percentages 

 differed considerably in some years . There are 

 no data upon which to explain this obvious corre- 

 lation. Perch were most abundant in 1937(167 

 percent) and were nearly as abundant in 1938 

 (159 percent). Their abundance was above aver- 

 age also in 1932 and 1933. Perch were least 

 abundant in 1930 (43 percent) and were below 

 average in 1931 and 1934-1936. The most pro- 

 nounced change in abundance occurred from 1936 

 to 1937. (1937 abundance percentage was three 

 times that of 1936). 



The very poor catches of walleyes in 1935 

 and 1936 were attributed to abnormally low water 

 levels . The vegetation along the shore, favorable 

 spawning and feeding grounds of minnows, was 

 exposed. It was thought that a subsequent reduc- 

 tion in forage fishes caused a loss in weight of 

 the predator walleyes so that many of marketable 

 length could no longer be caught in the 3-3/4-inch 

 meshes, thereby decreasing the catch in pounds 

 per unit of net. Figures were brought forward 

 to show that in 1934 the average weight of the wall- 

 eye in the commercial catch was 1 2 pounds but in 

 1936 it was only 0.9 pound. In 1938 the average 

 weight was again 1 . 2 pounds . The water level was 

 said to have been from 4-1/2 to 5 feet higher in 

 1938 than in 1936. 



Because 3-3/4-inch mesh did not take wall- 

 eyes of marketable size, the manager of the fisheries 

 in 1936 authorized mesh of 3 -1/2 -inches. The ef- 

 fect of this reduction in size of mesh apparently is 

 reflected in the increased catch per unit of effort in 

 1937. The still further rise in catch in 1938 is ex- 

 plained, in part at least, by the increased average 

 weight of the fish. The walleyes were in better con- 

 dition in 1938 than in several preceding years . 



It is not apparent why the catch of perch 

 should drop so low in 1936, but the reduction in mesh 

 size is responsible for part if not all of the rise in 

 catch in 1937 and 1938. 



Abun dance percentages of whitefish cannot be 

 considered dependable. Summer is a poor season 

 for capture of whitefish, and annual fluctuations in 

 catch per lift may depend more on limnological con- 

 ditions that determine whether whitefish are present 



24 



