F-22 



Table 6.? Estimates of krill density in sv/arras 



« Absolute range 521-49,153 



Ag a first approximation therefore the acoustic estimates largely confirm those from 

 plankton hauls. From the point of undertaking fishing operations it is clearly possible to 

 detect krill concentrations using echosounders. Tlie magnitude of any diurnal vertical move- 

 ment is likely to be of little consequence in catching technique. However, greater sophisti- 

 cation is required to quantify echo sounder indications in order to use them for estimation 

 of standing stock or as "ground truth" for estimation by satellite imagery. 



6.6 Food and Feeding 



An extensive study of the food organisms found in the stomachs of a large sample of 

 Euphausia guperba was made by Darkley (1940). The species list that he gives is largely 

 confirmed by the observations of Ilart (both lists are discussed at length by Marr 1962, 

 pp. 172-176). iniile there are local differences in the occurrence of the various species 

 (see also Ilustedt 1958, Nemoto I968, Kawamura, in press) the diatoms clearly predominate 

 from these analyses. The preponderance of diatom remains is generally thou^t to result 

 from the relative indigestibility of the siliceous frustules and therefore probably does not 

 represent the true situation (see discussions by Marr I962 and Mauchline and Fisher 1969) 

 and althouf^ the feeding appendages are adapted to a herbivorous diet it seems clear that, 

 when necessary, representatives of other groups can be taken. Mauchline and Fisher (I969) 

 list the following groups as being represented in the diet:- 



Algae, DiatcMS, Dinoflagellates, Tintinnids, Radiolarians, Foraminifera and Crustacea. 



In addition, Pavlov (1971) increases the list to include detritus and in extreme cases 

 cannibalism. As already mentioned vdth regard to distribution detritus may well represent a 

 major part of the diet in winter although there are no results to confirm this. 



