A TOWED PUMP AND SHIPBOARD 

 FILTERING SYSTEM FOR SAMPLING 

 SMALL ZOOPLANKTERS 



by 



Charles P. O'Connell, Fishery Biologist 



and 



Roderick J. H. Leong, Fishery Biologist 



Bureau of Commercial Fisheries Biological Laboratory 



U.S. Fish and Wildlife Service 



La Jolla, California 



ABSTRACT 



The construction, operation and performance of a towed pump and shipboard 

 filtering system for sampling small zooplankters is described. The system is com- 

 posed of (1) a collector containing a pump towed by a suspension unit consisting of a 

 hose through which runs a steel cable for support and an electric line to power 

 the pump, (2) a winch, and (3) a filtering unit composed of a watermeter, a double- 

 throw valve and two filtering funnels. The towed collector and its electrically driven 

 pump operate satisfactorily to a depth of 5 or 6 meters at a vessel speed of 9 knots. 

 The winch is inadequate for the task it is meant to perform, but demonstrates that it 

 is practical to use a winch with a hose and cable suspension. The filtering unit, easily 

 operated by one man, is highly satisfactory. Discrete samples can be taken at 

 intervals of a few minutes while traveling at vessel cruising speed by using the two 

 funnels alternately. Special samples and tests indicate that errors due to escapement 

 and entrapment of zooplankters and to mixing of zooplankters between consecutive 

 samples are negligible. It is concluded that the towed pump and shipboard filtering 

 system is a practical sampling tool that needs further modification for the full 

 utilization of its capabilities. 



INTRODUCTION 



In 1958 the Bureau of Commercial Fisheries 

 Biological Laboratory, La Jolla, California, 

 initiated a study of the relation between the 

 behavior of the Pacific sardine (Sardinops 

 caerulea) and the density distribution of its 

 planktonic food. The first phase of the pro- 

 gram was largely devoted to the development 

 of a towed pump and shipboard filtering unit 

 for quantitative sampling of the small zoo- 

 plankters that constitute the bulk pf the sar- 



dine's diet. Sampling surveys were carried 

 out with this apparatus in the fall of 1961 by 

 the Bureau of Commercial Fisheries research 

 vessel Black Douglas. The apparatus will be 

 described and evaluated in this report, and the 

 results of the 1961 surveys will be presented 

 in later reports as the samples are processed. 



A study of the density distribution of sardine 

 food organisms requires that the smallest 

 possible zooplankters be collected quantita- 

 tively. Hand and Berner (1959) found that 



