AN ECOLOGICAL RECONNAISSANCE OF THE DEEP SCATTERING LAYERS IN THE EASTERN TROPICAL PACIFIC.
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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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 RV 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 chlorophyll a 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. Author
- Biological Oceanography