198 



Conservation Department 



The apparatus used in collecting the drift food consisted of a 

 "drift net" (Fig. 2) and a "stop net" (Fig. 3). The drift 

 net collected the drift by straining the water arid retaining the 

 organisms. The stop net was placed 250 yards upstream above 

 the drift net and strained all the drift food from the water which 

 was being carried downstream from sources upstream, so that the 

 drift food could be taken from a given area of stream (250 yards) 

 over a standard period of one hour in each study. 



All the drift organisms from a 1-hour, 250 yard catch, were 

 weighed together, separate food organisms not being weighed 

 unless extra large individuals were taken which would throw the 

 weight off in proportion to numbers. 



Fig. 2. — Drift net in use 



Selection of areas in streams for study of available drift was 

 based on their ability to illustrate as far as possible the relative 

 amounts of available drift food found in given types of stream 

 environment. These fell roughly into four classes: arboreal 

 (forest covered), areas covered by thick growths of brush, semi- 

 exposed and exposed. No two selected areas will ever be exactly 

 alike for many factors other than merely cover or the lack of it 

 go into the making of any environment. 



Table 4 gives a summary of the results obtained. The right 

 hand column of figures gives the estimated production of drift 

 food in grams per 100 square feet of surface* for each type of 

 habitat. These estimates are based upon the average weight of 



* This includes not only animals found floating on the surface but also those 

 carried in suspension beneath the surface. 



