FISHERY BULLETIN: VOL. 76, NO. 1 



Table 6. — Composition of plankton in 6 day and 6 night collec- 

 tions at Bogen Island, Enewetak Atoll, site of strong currents.* 



'Currents during diurnal collections_32 to 90 cm/s, x = 57; currents during 

 nocturnal collections: 15 to 83 cm/s, x = 45. 



Figure 7. — Dascyllus reticulatus illustrates the tendency to- 

 ward a deep body in certain diurnal planktivores that is in 

 contrast to the tendency toward a more cylindrical body in many 

 others. 



Myripristis spp. and Apogon spp. were seen. 

 Furthermore, during extensive daytime observa- 

 tions here we failed to note the dense concentra- 

 tions of these and other nocturnal fishes in diurnal 

 shelters that were widespread and obvious where 

 currents were weak. 



Samples From Bogen Island 



PLANKTON.— The major materials taken in 

 the net at the Bogen Island site of strong tidal 

 currents were zooplankters and algae fragments 

 (Table 6). To facilitate comparisons with collec- 

 tions from the weak-current site, all volumes are 

 standardized to a 5-min collection. The table lists 



144 



volumes of plankters actually collected, as well as 

 volumes adjusted to the standard relative net 

 speed of 28 cm/s (the net speed at the weak-current 

 site). 



The zooplankters collected at Bogen Island, 

 grouped by major taxonomic categories and with 

 data pooled from the three collection depths (sur- 

 face, middepths, and near bottom), are listed in 

 Table 7. For the reasons given above concerning 

 volumes, the table lists numbers of plankters ac- 

 tually collected and numbers adjusted to the stan- 

 dard relative net speed. Additional data on 

 calanoid copepods (Table 8) are presented to sup- 

 port certain points developed in the Discussion. 



Possibly zooplankters attempting to hold sta- 

 tion above precise points on the sea floor would be 

 sampled less effectively by the stationary net dur- 

 ing the slower currents sampled at Bogen Island 

 than by the moving net used at Walt Island. We 

 discount this possibility as a significant source of 

 error, however, because we did not see such or- 

 ganisms during our underwater observations of 

 the operation, or when examining collections that 

 sampled a wide range of current velocities. 



GUT CONTENTS OF THE DIURNAL 

 PLANKTIVOROUS FISHES.— The gut contents 

 of diurnal fishes collected at the same time, and in 

 the same location, as the daytime plankton collec- 

 tions are listed in Table 9. Only a relatively few 

 nocturnal planktivores (all of them Myripristis 

 spp. and Apogon spp.) were seen during the limi- 

 ted observations in this habitat after dark, and 

 none were sampled. 



DISCUSSION 



We were unable to intensively sample more 

 than two stations in the limited time available to 

 us at Enewetak. Nevertheless, data collected at 

 these two sites under a variety of conditions, 



