-25- 



employed to estimate krill abundance have included trawling, 

 acoustic sounders, estimating amounts consumed by predators, and 

 estimating phytoplankton availability. In spite of these 

 efforts, there are no reliable estimates of krill standing 

 stock. Table 3, in presenting several biomass estimates, high- 

 lights the inherent uncertainties, evidenced by the wide range 

 of values. Standing stock estimates are as much as several 

 orders of magnitude apart, and estimates of annual production 

 also vary widely (Table 4) . 



5 . Reproduction 



Although there are several studies on Euphausiid reproduction, 

 (Marr, 1962; Mackintosh, 1972b; Makarov, 1974), the nature of 

 Antarctic krill 's breeding and reproduction is poorly under- 

 stood. Good general reviews on Euphausiid reproductive biology are 

 provided by Fraser (1936) , Bargmann (1937) , and Mauchline and 

 Fisher (1969) . 



Authors differ on essential criteria for breeding sites. 

 The main question is: can krill breed in pelagic oceanic areas 

 or must they depend on continental shelf areas? Eggs, shed up 

 to 500 meters below the water surface (Mauchline and Fisher, 

 1969), sink to depths of approximately 2,000 meters before 

 hatching. In areas less than 2,000 meters deep, the eggs come to 

 rest on the bottom. After hatching, the larvae slowly rise in 

 the water column maturing as they ascend (Figure 8) . In areas 

 deeper than 2,000 meters, it was thought that perhaps eggs would 

 sink so deeply as to prevent ascending larvae from reaching the 

 surface by the time they require rich phytoplankton on which to 

 feed. Hence shelf areas were thought to be important for proper 

 development of eggs (Fraser, 1936). However, evidence now 

 seems to suggest that the increased water density encountered at 

 the Antarctic Bottom Water interface may preclude sinking beyond 

 this point. Voronina (1974) related krill distribution to the 

 relative densities of water over which eggs are spawned. He 

 considered the density structure of the water column in different 

 areas an important factor in limiting the range where krill eggs 

 can develop to the optimal stage prior to ascending. 



6. Food Habits 



Food habits of krill have been studied by Barkley (1940), 

 Hustedt (1958), Marr (1962), Nemoto (1968), and Kawamura (1978). 

 Although there are differences in the authors' conclusions, there 

 seems to be general agreement that diatoms make up a major 

 portion of krill 's food. Kawamura (1978) stated that krill feed 

 almost exclusively on phytoplankton — predominantly diatoms, 

 and he found a high correlation between krill distribution and 

 waters which had relatively small sized diatoms. Areas in which 



