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<p>This reconnaissance is the first ecological study of the deep  scattering layers (DSL) in the eastern tropical Pacific. It was made  during two three month cruises of the R/V TE VEGA, one of which was  predominantly in the Gulf of California. The reconnaissance is based  on over 100 fathometer echograms and 100 trawls which fished for a period of one hour with an opening and closing Tucker midwater trawl.  Echograms of two fathometer frequencies (30 Kc and 11 Kc) indicated that  two latitudinal scattering zones may exist. Temperature, oxygen, light  intensity, faunal composition, and swimbladder morphology were investigated  with relation to the DSL. The oxyclines associated with the  eastern Pacific oxygen minimum zone seemed to have little effect on the  DSL. Possible further evidence for the migration of DSL organisms for  feeding purposes was apparent as the maximum night surface scattering  was observed at the depth of maximum Chlorophylla or phytoplankton.  Frequency comparisons indicated a possible gradient of the size of  organisms in the DSL with smaller organisms toward the top of the layer.  A twenty-four hour continuous observation of an equatorial Pacific DSL  diurnal cycle and an evaluation of possible scattering organisms are  included.
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<br>Subjects: Oceanography; Acoustics; Scattering; Biology; Biological oceanography; ASW</div>
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Dunlap, Calvin Ray, III</div>
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