F-21 



Table 6.6 Information on the vertical range of krill swarms 

 (From inforroation in Shevteov and Itokarov) 



Swarm density 



Several authors have published estimates of the density in terms of ntunber and weight 

 of krill within swanns. These are summarised in Table 6.7. 



Most of the estimates (Table 6.7) of 3v;arm density vjere made by means of acoustic fish- 

 finders in conjunction with actual catches. There are clearly several sources of possible 

 error in this type of estimation. Although the ochosounder may give some indication of the 

 vertical extent of the swarm it ivill give no inaication of its lateral size; also, it is often 

 difficult to confirm that a particular acoustic indication resulted in a particular catch. 



The two estimates given by Marr (I962) are based on separate obsei^ations. The figure 

 of one per cubic 'inch is based on the density estimated by an observer looking vertically 

 down into a swarm from above. The figure of one per ei^t cubic inches was calculated from 

 a single lateral haul in a large swarm (the net was towed for 36 sec at 1-J kt through the 

 swarm). Assuming a mean wei^it of one gramme per individual, this represents a density of 

 about 6kg/m^. 



