During the period between 15 July and 10 August 1947, the 

 USS NEREUS made a continuous fathogram from Pearl Harbor 

 to the arctic with an NMC-1 fathometer using 18-kc. sound 

 pulses. The itinerary was via Adak and the Bering Sea. This 

 fathogram shows indications of the development of the deep 

 scattering layer each day throughout the cruise whenever the 

 vessel was in deep oceanic water. The shoal depth of the 

 Bering Sea precluded the development of a deep layer of 

 scatterers and the fathogram shows no evidence of any layers 

 of scatterers in these areas. 



The NEREUS fathogram displays especially well the 

 morning descent and the evening ascent of scatterers. They 

 appear to migrate as a layer rather than diffused but the 

 movement of scatterers in depths less than 60 fathoms cannot 

 be determined because of masking by the qutgoing ping. 

 Although the diurnal vertical migration is well displayed, 

 the scatterers descended to a depth so great that, throughout 

 most days, they were beyond the range of good detection by 

 the echo sounder; therefore it was only sporadically recorded. 



On 20 July at noon position of latitude 44°49'N, longitude 

 175°19'W, the layer was prominently developed throughout 

 the entire day (fig. 41). This comparatively strong develop- 

 ment of the layer may have been caused by a higher concentra- 

 tion of scattering organisms in the productive waters of the 

 Aleutian (Subarctic) Current which lies between latitude 

 42°N and the Aleutian Islands. The development of the deep 

 scattering layer from 175 to 225 fathoms was in agreement 

 with depths observed elsewhere. Twice during this day, a 

 double layer appeared. Especially surprising was that, 

 although a portion of the scatterers rise at sunset, the rest 

 remained at a depth of 175 fathoms throughout the night. Al- 

 though the other tapes examined occasionally show sporadic 

 indications of a scattering layer at night, this was the only 

 record of a prominent and continuous layer throughout the 

 most of the night. 



Another interesting phenomenon noted only on the NEREUS 

 fathogram was the presence of a double layer descending each 

 morning during the period from 15 July to 18 July. These 

 double descending layers were separated by a time interval 

 of about 20 minutes and apparently were the result of the 

 downward migrations of two types of organisms that are 

 negatively phototropic to markedly different degrees. Yet, 

 at sunset of these same days, only a single ascending layer 

 was noted. 



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