have a negative reaction to artificial light, that is, they will 

 dive and disperse away from the light. After the light is 

 tiarned off the scatterers return, but not as quickly as they 

 dispersed. From the behavior of the scatterers it is believed 

 that they are biological in nature and are probably the shrimp- 

 like mysids. Mysids, about |-inch long, are characteristically 

 night feeders. 



The study of turbidity structure (figs. 7, 8, 9) revealed 

 no apparent difference between day and night, suggesting 

 that light scatterers may be predominantly smaller than the 

 sound scatterers. However, the two types may be closely 

 related to each other. The sound scatterers either move 

 nearer the coastline from deeper water daily, or rise from 

 the bottom. It is likely that the food for these organisms, 

 the phytoplankton, is most common in or near the thermo- 

 cline. This food (and to some extent the larger organisms) 

 is the principal cause of turbidity. Since the acoustic echoes 

 are patchy, it is probable that turbidity follows the same 

 patchiness. 



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Figure 17. Appearance of an echogram during the day 

 (A) and the following evening (B). 



22 



