Figure 6. — BT tracing made after sampling. 



level, where the thermocline started and where 

 the eggs decreased significantly, larvae in- 

 creased to 41 /m.3. They were moderately 

 abundant at 20- m. but were absent at greater 

 depths. These results are consistent with the 

 conclusion, based on a large number of net 

 hauls, that sardine eggs and larvae are re- 

 stricted to the upper mixed layer and upper 

 part of the thermocline (Ahlstrom, 1959). In 

 the present series the eggs were clearly con- 

 fined to the upper mixed layer, while the larvae 

 were found in moderate numbers in the upper 

 part of the thermocline as well as in the upper 

 mixed layer. 



Chaetognaths and doliolids occurred at all 

 sampling levels, but their vertical distributions 

 were very different (fig. 5). The chaetognaths, 

 mostly 3 to 6 mm. juveniles of Sagitta 

 euneritica , were sparse in the upper mixed 

 layer, increased at the thermocline, and were 

 abundant at the lower depths. The numbers of 

 doliolids (unidentified), about 1 mm. long, were 

 high in the upper levels, declined in the thermo- 



cline, and were low at the lower levels. Changes 

 in the abundance of other organisms (not 

 counted) were similarly striking. For example, 

 ostracods decreased in numbers and pteropods 

 increased, with increasing water depth. 



ADVANTAGES AND LIMITATIONS OF A 

 PUMP AND REELED HOSE SYSTEM 



The use of a pump and a reeled hose to 

 study vertical distribution is not new. Aron 

 (1958), in a historical review, listed several 

 workers who have used pumps to sample 

 plankton from various depths, 



A pump and reeled hose system has several 

 advantages over the closing nets used by 

 Leavitt (1935 and 1938), which are opened and 

 closed while being towed slowly at depth. The 

 basic advantage is that the stream of water is 

 delivered on board where it can be manipulated 

 and closely monitored. Salinometers, ther- 

 mometers, and other apparatus may be used 



