68 Conservation Department 



ill (lisMstor to fish propagation. Eacli must be present in the 

 required amount and each must be continuously renewed if the 

 whok^ is to operate constantly and smoothly toward the desired 

 result. 



Its Components and Amount. — The bulk of the lake macro- 

 l)]aiikt()n is matle up of 6 copepods, 6 cladocerans, 1 amphipod, 1 

 mj^sidacean, and a few insect larvae. The copepods include 2 

 species of Cyclops, 2 of Diaptomus and 1 each of Epischura and 

 Limnocalanus. The cladocerans include 3 species of Daphnia and 

 1 each of Bosmina, Leptodora and Sida. The other species, which 

 are recorded farther on, do not occur in sufficient numbers to 

 form an appreciable percentage of the total bulk. Among the 

 Crustacea in this lake the cladocera are of more value as fish food 

 than the copepods because they are both larger in size and occur 

 in much greater numbers. 



Some investigators determine the amount of plankton entirely 

 by weighing, others depend largely upon volumetric determina- 

 tions, while a third group make actual enumerations of the indi- 

 viduals of each separate species. In the present survey a combina- 

 tion of the last two methods has been employed. The total bulk 

 of each catch was measured in cubic centimeters and the per- 

 centage of each species was computed by an actual count of the 

 number of individuals present in a measured sample of the catch. 



These methods have conclusively proved two facts with reference 

 to the total amount of plankton. First the Crustacea are not uni- 

 formly distributed throughout the Avater of the lake; on the con- 

 trary the amounts obtained at different localities showed the great- 

 est inequality. Of the two hauls, made at adjacent stations at a 

 very brief interval of time and under almost identical conditions, 

 it repeatedly happened that one jaelded a total bulk too small to 

 be measured, while the other produced from 500 to 2,000 cubic 

 centimeters. Indeed, the chief characteristic of the amount of 

 l)lankton obtained in the various hauls was its excei)tional dis- 

 parity. In view of this fact it does not seem rational to make 

 any computation of the amount of plankton per cubic liter of 

 water or per square meter of the surface of the lake. But the 

 second fact is just as conclusive, namely, that the lake as a whole 

 contains an amount of plankton ami)ly sufficient to feed many 

 times the number of fish it contains. Wlien the investigation first 

 started each haul of the meter net lasted 15 minutes, but it was 

 (|iiickl3' manifest that the total bulk of plankton thus obtained was 

 far greater than could be adequately handled, and the haul was 

 reduced to 5 minutes. Even after this reduction the amount of 

 plankton in a single haul often reached 1,000 cubic centimeters. 



This means that the amount of fish food in the water of the lake 

 is so great that it could be stocked with a very large number of 

 fish fry without danger of depletion. The vai'ious hatcheries 

 around the shores of the lake can all be pushed to the limit of their 

 production, and the resultant fry can be put into the lake with the 

 certaintv that thcv will find an a])undan('e of good food. 



