SECT. 4] 



SOI'ND SCATTERING UY MARINE ORGANISMS 



509 



part of this volume. Tucker (1951) studied net hauls from about these same 

 areas and compared the catches with the distribution of sound-scattering as 

 determined by an 18 kc/s echo-sounder. He correlates shallower, weaker sound- 

 scattering with euphausids and deeper, stronger scattering with bathypelagic 

 fishes, mainly myctophids with gas-filled swim-bladders. Barham (1957) has 

 studied the scattering layers of Monterey Bay with a 17-18 kc/s echo-sounder 

 and compared these with net hauls made at frequent intervals over a two-year 

 period. He associates, as major scattering organisms, a lantern-fish and a 

 euphausid with 100-300-m layers and a second lantern-fish and a prawn with 

 300-500-m layers. It should be noted that both lantern-fishes so attributed 



n 1 1 r 



NISHT HAULS 



J — 



CATCH (myclophid fishes /hr) 



Fig. 9. Vertical distribution of myctophid fishes in number of fish per hour's haul for day 

 and night catches in deep water south of New England (see text). 



{Diaphus theta and Lampanyctus leucopsarus) have fat -filled rather than gas- 

 filled swim-bladders. 



Fig. 9 shows, from unpublished data of the authors, catches of myctophid 

 fishes made with an Isaacs-Kidd mid-water trawl in a water depth of about 

 2200 m, south of New England, in the summer of 1953. The catches come from 

 hauls of about three hours duration made wholly during hours of darkness or 

 hours of daylight and not at times when the principal scattering layer observed 

 was making its vertical migrations. The lantern-fishes comprised roughly half 

 of all fishes caught. The half not accounted for here paralleled the lantern- 

 fishes in their vertical distribution. Because of the nature of the net only large 

 planktonic crustaceans were caught, of which only euphausids were abundant. 

 The distribution of these was similar to that of the fishes. Scattering layer 

 records were made with a 12 kc/s echo-sounder and were of poor quality. The 



