128 



NOAA Technical Report NMFS 140 



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NOVA GULF OF GEORGES SOUTHERN GEORGES SOUTHERN 



SCOTIA MAINE BANK NEW ENGLAND SLOPE NEW ENGLAND 



SHELF SLOPE 



GEOGRAPHIC AREA 



Figure 1 1 8 



Density and biomass of Bivalvia in each of tlie six geographic areas. 



England Slope. Lowest abundance (34/m 2 ) was on 

 Georges Bank, but there the average size was greatest. 



The biomass of bivalves was exceptionally high (aver- 

 aged 166 g/m 2 ) on the Southern New England Shell 

 (Table 8; Fig. 118). Biomasses were moderate (30 to 77 

 g/m 2 ) in Nova Scotia, Gulf of Maine, and on Georges 

 Bank. Average biomass of bivalves was smallest (1 to 2 

 g/m'-') in the Georges Slope and Southern New En- 

 gland Slope areas. 



Frequency of occurrence was high in all areas, espe- 

 cially in the two slope areas where bivalves occurred in 

 89 .md 94% of the samples (Table 10). Georges Bank 



had the lowest (64%) rate of occurrence. In all other 

 areas the rate of occurrence was 80 to 89%. 



Bathymetric Distribution 



Bivalves were taken at depths from 3 to 3,820 m. They 

 were common in all depth zones but occurred in great- 

 est density (505 individuals/m 2 ) in shallow water (0 to 

 24 m) and diminished markedly with increasing water 

 depth (Table 11; Fig. 119). In the deepest zone samples 

 (2,000 to 3,999 m) their density was only 26/m 2 . The 

 decrease in density was quite uniform; the major decre- 

 ments in the trend were at about 25 m and 200 in. 



