174 



NOAA Technical Report NMFS 140 



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GEORGES SOUTHERN GEORGES SOUTHERN 

 SINK NE« ENGLANO SLOPE NE* ENGLAND 

 SHELF SLOPE 



GEOGRAPHIC AREA 



Figure 179 



Density and biomass of Mysidacea in each of the six geographic 

 areas. 



Frequency of occurrence of mysids was 

 higher (7 and 8%) in the intermediate car- 

 bon content classes than in the lower ones (3 

 and 5%) in which they occurred (Table 30). 



Decapoda — Decapods, although well rep- 

 resented in terms of the number of taxa that 

 were found in our quantitative samples (two 

 suborders and three sections contained 24 

 genera and 34 species, Table 4), did not rank 

 as highly in their contributions to the total 

 number of specimens (0.5%), or to total bio- 

 mass (0.8%) (Table 3). The apparent poor 

 showing of the class, the largest among all 

 classes of crustaceans, is misleading, precisely 

 because of the large size and mobility of many 

 of the representative species. These large, 

 highly mobile forms are more effectively 

 sampled by qualitative gear types, such as 

 dredges and trawls, than by quantitative grab 

 samplers. Thus the estimates of density and 

 biomass presented in this report, for this class 

 of crustaceans, should be considered to be 

 very conservative at best. Indeed, the taxo- 

 nomic list of decapods obtained by means of 

 qualitative sampling gears in our databases is 

 considerably more expansive than the one 

 included here in Table 4. Nevertheless, the 

 quantitative data reported in our report con- 

 tain a fair representation of the major forms 

 present in the region and constitute the most 

 extensive and complete set (known to us) upon 

 which to base our estimates. 



Decapods were not found in most of the 

 Gulf of Maine. For the most part, they are 

 restricted to the Southern New England con- 

 tinental shelf and upper slope and to Georges 

 Bank; some occurred on the western portion 

 of the Nova Scotia shelf and the western basin 

 of the Gulf of Maine. Average densities were 

 low, ranging from 1 to 49 individuals/m , over 

 most of their range in the study area. Size of 

 captured specimens tended to be smaller than 

 the overall average for this class, reflecting the 

 bias imparted by the relatively small area 

 sampled by the quantitative grabs used in our 

 study. The smaller members of this group were 

 less adroit at avoiding capture. The average size 

 of caridian shrimps ranged from 20 to 40 mm; 

 occasional larger specimens (40-60 mm) were 

 captured. The latter were usually representa- 

 tives of more sedentary, less active taxa, such as 

 the burrowing sand shrimp Crangon septem- 

 spinosits. Average anomuran size ranged between 

 4 and 20 mm carapace length. Most frequently 

 captured were representatives of the relatively 



