Table 10. --Compariaon of differences in composition of zooplankton catches obtained 



with Clarke-Bumpus samplers using 56XXX grit gauze nets ( Hugh M. Smith 

 cruise 16, horizontal hauls) and those obtained with 1 -meter (mouth diam- 

 eter) 30XXX grit gauze nets (Hugh M. Smith cruise 5. oblique hauls) 



plankton. The greater retention of Foraminifera, small invertebrate eggs, and Appendicularia 

 (Tunicata) is also evident. The other major groups of the zooplankton are apparently captured in 

 about equal proportions by the two methods. 



The tendency for the capture of smaller organisms with the finer meshed, smaller 

 mouthed Clarke-Bumpus gear, noted qualitatively above, can be expressed quantitatively by com- 

 parison of average size of organisms taken on cruises 5 and 16, from which both volumes and 

 counts are available (table 11). In most of the hauls of cruise 16, employing the Clarke-Bumpus 

 gear, the average size of organisms was between 1 and 3 x 10"* cc. , while in nnost of the hauls of 

 cruise 5 the average size was between 6 and 14 x 10" cc. The mean size of organism in the 

 samples (each sample given equal weight) was about five times as large for the coarse-meshed 

 meter net of cruise 5 as for the fine-meshed nets of cruise 16. It is quite obvious that the gear of 

 the two cruises exercised a strong size selection in sampling the plankton community. The volume 

 of catch was not greatly different however, indicating that with the larger net of coarse mesh the 

 loss in small organisms was compensated by the less successful dodging of the larger organisms. 



19 



