Figure 2. — Photographs showing the general construction of the winch: (a) general view of the winch and stern 

 roller; (b) details of support for the shells; (c) passage of hose from second to third level; (d) the winch motor 

 (chain removed) and hand brake. 



of water. The winch was stopped at 5-m. inter- 

 vals to obtain temperature readings from the in- 

 coming stream. Comparison of these tempera- 

 tures to a BT trace, made immediately after the 

 pump was retrieved, indicated that the hose was 

 nearly vertical. Only at the 35-m. level, where 

 the temperature of the incoming stream was 

 15.1° C. and the BT temperature was 14.4°C, 

 was there any noticeable discrepancy. The pe- 

 riod of flushing, which is necessary to remove 

 temperature effects from previous depths, was 

 probably too short at that level. The BT profile 

 and temperature measurements are discussed 

 further in the section on egg distribution. 



The watermeter indicated that the rate of flow 

 varied little within each of the above trials but 

 differed between them. In the least variable 

 trial, the rate ranged from 79 to 81 liters per 

 minute and in the most variable trial the range 

 was 71 to 77 liters per minute. The rate of flow 

 tended to be slightly higher when the pump was at 



greater depths, possibly because friction is 

 less in a straight hose than in a coiled hose. 



SOURCES OF ERROR 



Errors in sampling marine organisms gen- 

 erally fall into two categories. First, a sampler 

 may be unable to collect effectively owing to 

 the behavior of the organisms: avoidance for 

 example. Second, the organisms can be col- 

 lected but the sampler may introduce error: 

 inaccurate measurements of water volume for 

 example. 



No attempt was made to analyze the effect of 

 organism behavior on pump samples but some 

 attention was given to possible sources of 

 error in the pump system. Water volume is 

 measured accurately but errors may arise 

 from fragmentation of organisms by the pump 

 impeller, uneven transport of organisms 

 through the hose, and escapement of organisms 



