to measure water properties directly, or water 

 samples may easily be collected for analysis 

 on shore. Hydrographic and BT casts taken in 

 conjunction with a net series can provide this 

 information, but they are separated temporally 

 and spatially from the organisms in the sample. 

 The pump and reeled hose make it possible to 

 observe changes in water properties as they 

 occur. The temperature readings on deck show 

 when the thermocline is penetrated, and inspec- 

 tion of the plankton samples indicates when the 

 vertical range of an organism has been ex- 

 ceeded. Strainers of variable mesh sizes may 

 be used because clogging can be observed and 

 controlled even when the mesh openings are 

 small. 



The pump and reeled hose system has some 

 severe limitations in comparison with plankton 

 nets. The vertical series described in this 

 paper was taken in an unusually high concen- 

 tration of eggs and larvae. Standardization of 

 the numbers by Ahlstrom's method (1948) for 

 oblique net tows indicates an abundance of 

 about 6,100 eggs and 7,200 larvae under 

 10 m. 2 of sea surface. Net tow data show that 

 patches of sardine eggs generally occur in 

 much lower concentrations. In such lower con- 

 centrations the pump would not be very ef- 

 fective because the volume of water strained 

 in a reasonable length of time would produce 

 insufficient numbers of eggs and larvae for 

 meaningful analysis. Also, the large mouth 

 opening of nets decreases the opportunity for 

 escapement of the larger, more motile or- 

 ganisms. The intake of the pump is small, 

 and even if a large organism is captured, it 

 may be mutilated beyond recognition. Thus, 

 nets and pumps complement each other; each 

 has advantages for sampling particular seg- 

 ments of the biomass. 



LITERATURE CITED 



AHLSTROM, ELBERT H. 



1943. Studies on the Pacific pilchard or sar- 

 dine ( Sardinops caerulea ). 4-Influence 

 of temperature on the rate of develop- 

 ment of pilchard eggs in nature. U.S. 

 Fish and Wildl. Serv., Spec. Sci. Rep. 

 Fish. 23, 26 p. 



1948. A record of pilchard eggs and larvae 

 collected during surveys made in 1939 

 to 1941. U.S. Fish and Wildl. Serv., 

 Spec. Sci. Rep. Fish. 54, 76 p. 



1954. Distribution and abundance of the egg 

 and larval populations of the Pacific 

 sardine. U.S. Fish and Wildl. Serv., 

 Fish. Bull. 93, vol. 56, p. 83-140. 



1959. Vertical distribution of pelagic fish 

 eggs and larvae off California and Baja 

 California. U.S. Fish and Wildl. Serv., 

 Fish. Bull. 161, vol. 60, p. 107-146. 

 ARON, WILLIAM. 



1958. The use of a large capacity portable 

 pump for plankton sampling, with notes 

 on plankton patchiness. J. Mar. Res. 

 3: 158-173. 

 LEAVITT, BENJAMIN B. 



1935. A quantitative study of the vertical 

 distribution of the large zooplankton in 

 deep water. Biol. Bull. 68(1): 115-130. 



1938. The quantitative vertical distribution 



of macro- zooplankton in the Atlantic 



Ocean Basin. Biol. Bull. 74(3): 376- 



394. 



O'CONNELL, CHARLES P., and RODERICK 



J. H. LEONG 



1963. A towed pump and shipboard filtering 

 system for sampling small zooplank- 

 ters. U.S. Fish and Wildl. Serv., Spec. 

 Sci. Rep. Fish. 452, 19 p. 



MS. #1588 



GPO 914-166 



