BATHYPELAGIC SQUID BATHYTEUTHIS 171 



Vertical Distribution by Size 



The sizes (ML) of 56;^ si)ecimens of B. ahyssicoJa are plotted 

 against depth of capture in fignre 64. The plot shows a tendency for 

 the smaller specimens to be located at shallower depths and the larger 

 specimens to be concentrated at greater depths. Although no sharp 

 break occurs on the overall chart, the division between the shallow and 

 deep concentrations lies at about 30 mm ]ViL. This length also corre- 

 sponds with the size above whicli all males are fully mature and all 

 females are either well advanced in maturity or are fully ripe. The 

 following discussion determines the degree to which the size-segments 

 of the sample population are concentrated at difference depths. 



Thirty-six percent (204 specimens) of tlie total population is com- 

 posed of specimens less than 30 mm in ML ; the remaining specimens 

 range from 30 mm to 75 mm in ML. Eighty-tliree percent (167 speci- 

 mens) of the small sj^ecimens was captured between 500 and 2000 m ; 

 111 of these (55% of the small population) came from 500-1300 m. 

 The major concentration, representing 46.3% of the small population 

 (94 specimens), lies between 800 m and 1300 m; 40 specimens (20%) 

 range between 500 m and 1000 m, and 8.4% lie between 500 m and 

 750 m. Thirty-six specimens (17%) come from nets that fished below 

 2000 m; the points are scattered and it is probable that the bulk of 

 these came from the shallower tows, perhaps from the zone of con- 

 centration (800-1300 m) or from a possible secondary concentration 

 at 1700-2000 m. If the specimens below about 2000 m were propor- 

 tionally redistributed according to the calculations below they would 

 lie within the layer of abundance. 



The greatest proportion (72.5%) of the individuals in the segment 

 of the population above 30 mm was captured below 1500 m; 51% of 

 the large population is concentrated between 1650 m and 2200 m, with 

 13% below 2200 m. The remaining 27.5% of the large population is 

 distributed between 625 m and 1500 m in the following proportions: 

 3.3% between 625-750 m; ^% between 625-1000 m; 18.6% between 

 1000-1500 m. The graph (fig. 64) shows some specimens plotted below 

 2500 m; but the calculations made in the preceding section indicat:e 

 that few B. ahyssicola live below 2500 m; therefore, the specimens 

 deeper than 2500 m should be proportionally redistributed in the layer 

 of abundance between 1650 m and 2500 m (see calculations below). 

 Between 1500 and 2200 m are 187 specimens that range from 30 mm 

 to 50 mm in ]VIT^; this group represents 52% of the large population 

 and 33% of the total population. 



Tables IX-XI summarize the distributions of specimens in the 

 sample population by size at the various depth increments. A total 

 of 490 specimens lies between 1000 m and 2500 m ; these account for 



321-534 0—69 12 



