deep scattering layer is presumably caused by light sensi- 

 tive organisms, this shoal depth of the layer may be corre- 

 lated with the overcast sky condition on this date, with the 

 low angle of the sun at this latitude, and with the high opacity 

 of the water related to high organic production. All of these 

 factors would decrease the depth of light penetration in the 

 ocean. In the late afternoon, the layer descended to a greater 

 depth of from 125 to 175 fathoms and became more strongly 

 developed. Shortly prior to sunset at 2051 LCT, the USS 

 NEREUS reached the shallow water of the Bering Sea shelf; 

 observations showed that the deep scattering layer ends 

 where it abuts against the continental slope. 



During the remainder of the arctic passage, the USS 

 NEREUS was in the shoal shelf waters of the Bering and 

 Chukchi Seas. These shoal waters (always less than 75 fath- 

 oms and generally less than 30 fathoms) precluded the de- 

 velopment of a deep scattering layer. Although shoal scatter- 

 ing layers are occasionally observed in shallow water, none 

 were present on the fathogram of the USS NEREUS. This may 

 be due to the absence of shallow scatterers or, more likely, 

 to the low gain setting used in obtaining bottom echoes in 

 shoal water, a setting usually insufficient to bring in echoes 

 from scatterers. 



ZOOPLANKTON 



During the arctic cruise, the USS NEREUS occupied a 

 series of stations for taking net hauls: seven stations along 

 a line between the Hawaiian and the Aleutian Islands; twenty- 

 one stations on a line extending northward from the Pribilof 

 Islands, through the Bering Strait to 72°N latitude in the 

 Chukchi Sea, and back to Kotzebue Sound; and one station just 

 south of Unimak Island. Only the samples from this last 

 station and the stations north of the Aleutian Islands will be 

 considered here in some detail (see fig. 55). The samples 

 were all collected within the period, 27 July to 12 August; 

 hence they are representative of summer conditions only. 



These collections form a valuable supplement to the 

 series collected by the U. S. Coast Guard Cutter CHELAN 

 in 1934** and contribute in no small way to our slowly accumu- 

 lating knowledge of the plankton biology of these remote 

 areas. In a later report it is planned to integrate more fully 

 the findings of these two surveys. 



