THE NAVY OCEAN SCIENCE PROGRAM 



47 



At dawn some scattering layers migrate from near the svirface to depths ais 

 great as 200 to 500 fathoms. Others may not migrate at all, while still others (not 

 shown) rise from greater depth toward the surface at dawn. These two records 

 show animals dispersed evenly in layers (upper record) and others that con- 

 centrate in groups (lower record). Echoes of the groups are recorded as the ship 

 passes over, forming a crescent pattern. On both records the echo from the sea 

 floor appears below the layers at nearly constant depth. 



