164 



NOAA Technical Report NMFS 140 



major difference was that cumaceans were 

 twice as numerous as isopods, but the 

 relative densities of the two groups corre- 

 sponded rather closely. The geographic 

 distributions of the two groups were also 

 similar (see Fig. 154). 



Frequency of occurrence of isopods in 

 the samples was moderate (48% of the 

 samples) on Georges Bank and the South- 

 ern New England Slope. In the other four 

 geographic areas isopods occurred in 20 

 to 35% of the samples (Table 10). 



Bathymetric Distribution 

 Isopods occupied a very wide depth range 

 (5-3,820 m) and specimens were present 

 in all eight depth classes (Table 11; Fig. 

 168). Densities were highest (22-38 indi- 

 viduals/m 2 ) in the two shallowest depth 

 classes and decreased as water depth in- 

 creased. Lowest density (0.4/m 2 ) was en- 

 countered in water depths between 1 .000 

 and 2,000 m. In samples from the deepest 

 strata (2,000-4,000 m) the density was 

 1.9/m 2 . 



Biomass values exhibited similar pat- 

 terns in relation to water depth (Table 

 13; Fig. 168). The average biomasses of 

 isopods were much higher (ranging from 

 0.15 to 0.66 g/m' J ) in water depths less 

 than 500 m than in deeper water where 

 the average biomass ranged from only 

 0.01 to0.02g/m-. 



Frequency of occurrence of isopods was 

 highest (46 to 69%) in samples from wa- 

 ter depths ranging between 25 and 100 

 m. Occurrence rates were intermediate 

 (12-20%) in samples from outer conti- 

 nental shelf and continental slope depths 

 (100-2.000 m) and moderately high 

 (43%) at depths greater than 2,000 in 

 (Table 15). 



Relation to Sediments 



Isopods were found in all of the sediment 

 types occurring in the study area (Table 

 16; Fig. 169) but were three to seven times 

 more numerous (22.4 individuals/ m J ) in 

 sand substrates than in any other type of 

 bottom. The average density of isopods in 

 the other sediment types was fairly uni- 

 form, ranging only from 3 to 7/nr. 



The average biomass of isopods was 

 highest (1.36 g/m 2 ) in till substrates 

 (Table 18; Fig. 169). Also, as was the case 



5 

 O 



OS 



CE UJ 

 UJ CC 

 CD < 

 13 



2° 



2 W 



i 



NOVA 

 SCOTIA 



I — | NUMBER 

 ■I WEIGHT 



fk rr 



z 

 o 



X UJ 



a z 



* or 



* v> 



GULF OF GEORGES SOUTHERN GEORGES SOUTHERN 



MAINE BANK NEW ENGLAND SLOPE NEW ENGLAND 



SHELF SLOPE 



GEOGRAPHIC AREA 



Figure 167 



Density and biomass of Isopoda in each of the six geographic areas. 



