172 



Ir.i.iNOis Natural Hisiorv Survi-v Hui.i.nTiN 



Vol. 27, Art. 2 



crop that was harvested. 'I'lie total 

 amount of fish in a lake or stream at any 

 jiiven time was the standinj^ crop; when 

 the standinjj; crop reached "saturation 

 it represented the carr\ in^ capacity of the 

 lake or stream. Thompson believed that 

 the food resources and the carryin^^ ca- 

 pacity of a body of water remained fairly 

 constant but that the number of iish 

 could vary widel\ . He reasoned that, if 

 the weifi:ht of fish remained constant, then 

 the removal of some fish would furnish 

 more food per individual for those re- 

 maininj:;, and the jj;rowth rate would in- 

 crease ; if more fish were planted, less 

 food would be available per individual, 

 and the ji:rowth rate would decrease. To 

 further this thesis, he was able to demon- 

 strate from his own laboratory experi- 

 ments that at a water temperature of 70 

 degrees F. a 10-inch bass required as food 

 an amount of minnows equal to three- 

 fourths of 1 per cent of its body weijjht 

 per day in order to maintain a constant 

 weight; and that, at an optimum feeding 

 rate, 2.5 pounds of minnows were re- 

 quired to produce 1 pound of bass. 



Complete censuses of nine Illinois lakes 

 subject to floods and indiscriminate stock- 

 ing showed that, although 46 different 

 species were present, only 10 species of 

 fish comprised more than 1 per cent each 

 of the total weight of all fish. The rough 

 fish listed were redmouth buffalo, mon- 

 grel buffalo, and carp ; forage fish were 

 gizzard shad and golden shiner; catfish 

 included only the black bullhead ; the pan 

 or fine fish were bluegill, white crappie, 

 and black crappie; and the only game 

 fish was the largemouth bass. These 

 species must be considered as showing 

 superior adjustment to the pond habitat 

 in Illinois. 



Thompson had observed cycles in fish 

 that were the result of interspecific and 

 intraspecific competition. The "fine" fish 

 in Lake Senachwine (Illinois) amounted 

 to about 50 to 55 pounds per acre, regard- 

 less of the niunber of fisli or the area of 

 the lake. In some years there were 10 

 times as maii\ fish as in other years, and 

 the indiviihial tisli averaged one-tenth the 

 weight of the indivitiual fish of other 

 years. I^arge broods of crappies were pro- 

 duced at intervals of about 4 years, and 

 (hiring interim seasons the\' controlled the 



survival of their own young and the 

 young of other species. 



Thompson attempted to construct a 

 theoretical maximum cropping rate for 

 any water area as a percentage of its 

 carrying capacity. He believed that the 

 cropping rate was related to latitude 

 (length of growing season). He estimat- 

 ed annual cropping rates for Vilas Coun- 

 ty and Madison, Wisconsin; Urbana and 

 Cairo, Illinois; Memphis, Tennessee; 

 Jackson, Mississippi; and New Orleans, 

 Louisiana. He assumed that in northern 

 Wisconsin about 21 per cent of the carry- 

 ing capacity could be replaced each year ; 

 in New Orleans the replacement could 

 be as much as 118 per cent; other loca- 

 tions fell between these extremes. 



Thompson also presented the idea that 

 fish predators were probably beneficial, al- 

 though he gave no data to back this 

 assumption. 



THE LAST TWENTY YEARS 



With the death of Robert E. Richard- 

 son in 1935, the aquatic biology staff of 

 the Illinois Natural History Survey was 

 reduced to Thompson and one full-time 

 field assistant ; however, several graduate 

 students were working under Thomp- 

 son's direction. At that time, Thompson I 

 was interested in beginning some pond ■ 

 management investigations. As a result 

 of a policy of expansion for the Section 

 of Aquatic Biology, I was employed on 

 January 1, 1938, to work with Thompson 

 on ponds. To gather experience in a 

 new censusing technique that involved 

 poisoning fish with rotenone, a technique 

 developed by R. W. Eschmeyer in Mich- 

 igan, Thompson and I made a trip to Ann 

 Arbor, where Eschmeyer was censusing 

 several small Michigan lakes. We helped 

 in one of the censusing operations and 

 were served some of the poisoned fish at 

 the home of Dr. Carl L. Hubbs. 



Returning to Illinois, we (with the 

 help of Donald F. Hansen) began cen- 

 susing ponds, one of the first of which 

 was Homewood Lake, a 2.8-acre pond 

 on the property of the Homewood Fishing 

 Club on the outskirts of Decatur, Illinois, 

 h'rom the standpoint of public relations, 

 the operation was a huge success. The 

 pond contained mostly carp, buffalo, giz- 



