BATHYPELAGIC SQUID BATHYTEUTHIS 167 



In the overall productive layer (500-2500 m) 21 two-hour tows 

 would have been expected to catch 21X2.63 specimons=55 specimens. 

 The actual catch (33 specimens) in the 2500-3000 m layer was only 

 60% of the expected. 



Further, to determine if the specimens were captured in the deep 

 layer or in the productive layer while the nets were set and hauled 

 through it, the factor of time must also be considered : the average time 

 required for a tow below 2500 m is 5.3 hours, with two hours spent 

 towing at depth and 3.3 hours spent setting and hauling. Tlius, it re- 

 quires 3.3 hours to cover 5000 m (2500 down, 2500 up) giving an aver- 

 age set-haul rate of 1500 m per hour. Since no B. abysslcoJ-a, are caught 

 in the upper 500 m (1000 m up and down), about 0.7 hours can be sub- 

 tracted from the travel time leaving 3.3 — 0,7 = 2.6 hours during which 

 the net is in the productive zone between 500 and 2500 m. (Another 

 approach: the net has to pass tlirough 4000 m of productive zone 

 (2500-500 = 2000; 2000X2 = 4000) which requires 4000^1500 or 2.6 

 hours.) If the average catch is 2.63 specimens per two-hour tow in the 

 productive area, then 3.42 specimens would be expected to be caught 

 in 2.6 hours while the net passed down and up through the zone of 

 abundance (2.6X2.63 = 6.85; 6.85-^2 = 3.42). Since only 1.57 speci- 

 mens were captured per two-hour tow below 2500 m, probably no speci- 

 mens were captured below 2500 m, i.e., B. ahyssicola does not normally 

 live below 2500 m. 



Since the 2250-2500 m zone shows some fall-off in the graph (fig. 

 62), the same method can be applied to the tows taken below 2250 m 

 in an effort to determine if the lower limit of distribution is shallower 

 tlian 2500 m : 



Total number of 2-hour tows between 500-2250 m=196 



Total number of specimens captured between 500-2250 m=510 



Average number of specimens captured per 2-hour tow between 500-2250 



m=2.60 

 Total number of 2-hour tows below 2250 m=40 

 Total number of 2-hour tows between 2250-2500 m=:19 

 Total number of specimens captured below 2250=86 

 Total number of specimens captured between 2250-2500 m=53 

 In the layer below 2250 m forty 2-hour tows averaged 2.15 specimens per tow. 

 In the layer between 2250 and 2500 m nineteen 2-hour tows averaged 2.79 



specimens per tow. 

 In the productive layer 40 tows would be expected to catch 104 specimens 



(40X2.60=104). The actual catch was S6 or 82% of the expected catch. 

 In the productive layer 19 tows would be expected to catch 19X2.60=49.4 



specimens. The actual catch was 53 or 9% greater. 



Again the time factor of the nets passing through the productive 

 layer should be taken into consideration. The same times required for 



