Figure 7. — Symmetrical ripple marks on the sea bottom at station 45. Identifiable animals: A. red hake, Urophycis 

 chuss; B. hermit crab; C. sand dollar; D. common northern moon-shell, Lunatia heros . Scale bar is 10 cm. long. 



on Georges Bank. Symmetrical sediment 

 ripples having crests spaced at roughly 10- cm. 

 intervals are present in photographs taken at 

 66 m. (station 42) and at 82 m. (station 45), 

 see figure 7; they are interpreted as having 

 been formed by wave action. A large series 

 of pronounced asymmetrical sand ripples at 

 64 m. (station 44; illustrated in fig. 8) indicates 

 a moderately strong water current flowing 

 from southeast to northwest (340°). Bottom 

 water currents judged from similar data from 

 the Continental Shelf off northeastern United 

 States were reported by Emery, Merrill, and 

 Trumbull (1965). They reported the currents 

 on southeastern Georges Bank to be flowing 

 from the northeast and northwest, rather than 

 from the southeast. This diversity of direction 

 suggests that tidal current is the principal 

 force producing these ripple marks. 



No sequential sediment markings indicative 

 of water movement are apparent in the photo- 

 graphs from the sampling station south of 

 Martha's Vineyard. Deformations in the sedi- 

 ment are irregularly spaced and of different 

 sizes and shapes. They appear to have resulted 

 from animal activities. 



COMPARATIVE ESTIMATES OF FAUNA 



DENSITY FROM DREDGE COLLECTIONS 



AND SEA-BOTTOM PHOTOGRAPHS 



This section deals with the kinds of animals 

 and the numerical density of each kind as 

 detected in the photographs and caught in the 

 dredge. The two major faunal categories are 

 treated separately under the headings "Epi- 

 benthic Invertebrates" and "Fishes." Emphasis 

 is given to the relative accuracy of the two 

 methods (dredging and photography) used in 

 estimating the density of benthic animals. 



Epibenthic Invertebrates 



Accurate and economical methods for ob- 

 taining quantitative estimates of epibenthic 

 invertebrate animals in sublittoral and deep- 

 sea environments have yet to be developed. 

 Older techniques for determining relative 

 densities or approximate quantities are dredg- 

 ing (collecting samples with an oyster dredge, 

 scallop dredge, or similar device towed along 

 the sea bottom) and trawling (towing a net 

 such as an otter or shrimp trawl). More 



