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this hypothesis. The basic idea is that krill are swept around 

 in cyclonic gyres with new individuals entering but few leaving 

 (Beklemishev, 1960; Makarov, 1972; Treshnikov, 1971). 



2 . Movements 



In addition to the horizontal movements that may occur as 

 previously suggested, krill are known to make localized horizontal 

 movements into high density patches or swarms (Hardy and Gunther, 

 1935; Gunther, 1949; Peters, 1955; Marr, 1962; Komaki, 1967). 

 These patches vary in size and sex ratio and sometimes may be 

 composed of individuals of the same age class (Marr, 1962) . 

 Figure 7 illustrates the general dimensions of several observed 

 krill swarms. Mackintosh (1966) described swarms made up of 

 juvenile and adult krill densely concentrated in the surface layer, 

 In the summer, swarms mostly remain out of sight beneath the 

 surface in darker waters by day while rising to upper waters 

 strata to feed in the evening. 



Marr (1962) stated that dense krill concentrations are 

 likely to occur in the top 100 meters of the water column with 

 the top ten meters being the depth most frequently used. He also 

 described diurnal vertical migration patterns. His observations 

 were supported by Shevtsov and Makarov (1969) as well as Pavlov 

 (1969, 1974) who observed diurnal vertical migrations within the 

 top 80 meters of the surface water. The authors associated 

 these extensive daily movements with feeding. Apparently krill 

 ascend as a swarm to reach the feeding areas where they disperse 

 to feed and eventually regroup before descending. 



3. Stock Identification 



It is not known if separate stocks of krill exist. Clearly 

 the existence of races or stocks would critically influence 

 management plans for a krill fishery. Nemoto et al. (1971) 

 demonstrated the development of clines in North Pacific 

 Euphausiids. Makarov (1974) and Mackintosh (1973), suggested 

 that there may indeed be separate Antarctic krill stocks. They 

 feel stocks might develop due to limited horizontal mixing of 

 the gene pool. Recent work by McWhinnie and Denys (pers. comm.), 

 based on repeated sampling in two different areas (the east 

 Bellingshausen Sea and the Bransfield Strait) , also suggests the 

 possibility of separate krill stocks in the greater Antarctic 

 Peninsula area. Although preliminary analyses of biometric 

 measurements indicate possible stock differences, their findings 

 are tentative, and further electrophoretic analyses are planned. 



4. Standing Stock 



Estimating krill standing stock is difficult due to widely 

 variable krill densities caused locally by swarming. Techniques 



