182 U.S. NATIONAL MUSEUM BULLETEST 291 



successful in capturing this species (100 tows shallower than 500 m 

 were entirely unsuccessful). The caj^tures averaged 2.5 specimens per 

 total 2-hour tow, and they ranged from 1 to 24 specimens per tow. 

 Several tow^s caught large numbers of B. ahyssicola; these have a pro- 

 nounced effect on the overall catch figures. Sixteen 2-hour tows that 

 caught 9 or more specimens captured a total of 210 specimens. This 

 means that 11.8% of the 134 successful 2-hour tows accounted for 

 35.2% of the total sample. All but two of these stations were located 

 in regions of the Antarctic Convergence. The specimens are grouped at 

 the peaks of occurrence on the vertical distribution chart, and, in fact, 

 they are responsible for these peaks. Only one capture was in less than 

 1000 m (914 m) and only two were deeper than 2100 m (2150 m, 

 2269 m) . Table XIV compares the total nmnber of specimens captured 

 at depth intervals with the number taken in exceptionally successful 

 tows and indicates the influence of these tows on the distribution of 

 the total sample population. The major effect of the exceptional tows is 

 apparent when they are deleted from the curve of the bathymetric 

 distribution. This results in the smoothing out of the curve so that the 

 peaks of abundance shift from sharp, bimodal peaks at 1000-1500 m 

 and 1750-2250 m to a single major peak at the 1750-2000 m range 

 wdth very slight secondary peaks above and below this depth incre- 

 ment (fig. 69). The large number of specimens from relatively few 

 tows does not mean that the concept of the vertical distribution of 

 the total population has to be altered; instead it indicates that B. 

 dbyssicoJa has a patchy distribution, both horizontally and vertically 

 with peaks of abundance located under the region of the Antarctic 

 Convergence. 



Table XIV. — The influence of exceptionally successful tows on the total sample 



population 



