manner but with a different arrangement of 

 hose and pump in the fall of 1958 suggest the 

 probable order of escapement (table 1). The 

 average number of copepods between 200 and 

 500// in these earlier samples is 2,266, and 

 the average number between 500// and 1 mm. 

 is 612. Thus escapement of copepods in any 

 size category above 200// is not likely to be 

 more than a few percent. If necessary, es- 

 capement can probably be reduced by using 

 a filtering screen of smaller mesh size in 

 the collecting bucket. 



No other zooplankters appeared in the es- 

 capement samples except larvaceans. The 

 estimate for the first sample is 23, and none 

 were found in the other 4. Since larvaceans 

 are present in considerable numbers in the 

 samples collected during the fall of 1961, it 

 is assumed that the above represents a 

 negligible escapement. 



The main filtering screens in the funnels 

 are the only other obvious site of escapement. 

 Examination of 20 half-liter samples of water 

 taken from these screens at various times 

 during the 1961 fall surveys has revealed no 

 zooplankters. Though this result is encourag- 

 ing, the observations are too few to permit a 

 conclusive appraisal. The half-liter samples 

 are so small a fraction of the 600 liters or 

 so that are filtered during each 6.5-minute 

 interval, that the absence of zooplankters in 

 20 such samples could easily have occurred 

 by chance alone. Much more filtered water 

 will have to be examined. 



A simple calculation and a laboratory test 

 indicate that organisms are not displaced to 

 any significant degree as they are trans- 

 ported from the collector to the filtering 

 unit. The length of the entire hose is 210 

 feet. Assuming that 1/2 inch of the 2-inch 

 diameter of the hose on the winch is occupied 

 by the support and electrical cables, the 

 diameter can be considered 1.5 inches for the 

 entire length. The volume of the hose, there- 

 fore, is 



2 

 TTr Ik 



72.8 liters 



where r is the radius, 1 is the length, and k is 

 the factor for conversion of cubic feet to 

 liters. At the average delivery rate of 92 



liters pe." minute the volume of the hose is 

 turned over every 48 seconds, or eight times 

 during the course of each 6.5-minute sam- 

 pling interval. This was verified by the fact 

 that spurts of dye introduced into the pump 

 intake in a laboratory trough took about 50 

 seconds to reach the other end of the hose. 

 The spurts of dye, furthermore, showed very 

 little diffusion as they moved through the hose 

 (a transparent vinyl hose was being used at 

 the time of these tests), suggesting that sus- 

 pended organisms would approximately main- 

 tain their relative positions during transport. 



Zooplankters that do not descend into the 

 collecting bucket at the end of a sampling 

 interval are either deposited freely on the 

 inner surface of the filtering funnel or trapped 

 in the phytoplankton film clogging the main 

 filtering screens. Those deposited freely on 

 the surface could be washed into some sub- 

 sequent sample, thus decreasing sampling 

 accuracy. Those entrapped in the phytoplankton 

 would constitute a fraction of the sample that 

 is lost, also decreasing sampling accuracy. 

 Virtually no zooplankters could be detected 

 on the inner surface of the funnels by visual 

 inspection following 6.5-minute sampling 

 intervals, indicating that there is essentially 

 no loss of accuracy due to organisms remaining 

 freely on the filter surface. Considerable 

 numbers did remain on the surface, however, 

 during special sampling sequences where the 

 sampling interval was 2 hours rather than 

 6.5 minutes. Drainage rate was greatly re- 

 duced by heavy clogging of the bucket screens, 

 and many zooplankters settled out and remained 

 on the inner surface of the funnel as the 

 water receded after the friction cap was 

 removed from the bucket screen. Thus rapid 

 drainage is necessary to insure that all or 

 most of the zooplankters captured during a 

 sampling interval are deposited in the collect- 

 ing bucket. If sampling intervals are to be 

 longer than a few minutes, or if the rate of 

 clogging is increased by a greater rate of 

 water delivery or the use of a finer mesh 

 screen in the bucket, the area of the bucket 

 screen would probably have to be enlarged 

 to achieve rapid drainage. 



Examination of the phytoplankton film, which 

 was removed from the funnels and preserved 



16 



