FISHERY BULLETIN; VOL. 74, NO. 2 



30' 



20' 



10' 



0°- 



160= 



140"= 



140* 



120 



100* 



Figure l. — CompEirison of the known occurrence of spotted porpoise in the eastern Pacific (above) 

 with average thickness of the subsurface layer of water (contours in meters) in which the dissolved 

 oxygen is less than 0.25 ml/liter (below, after Knauss 1963). The entire layer lies above 1,000 m. 



232 



