As a result of intensive hunting of whales, their initial numbers have 

 been reduced over the past 40 years by 85-90% (Mackintosh, 1970), 

 correspondingly decreasing the consumption of their prey. Let us attempt 

 to discuss the results of these changes on the example of E. superba . We 

 could hardly expect that the increase in its quantity, estimated as 30 

 million tons (Mackintosh, 1970), would cause an increase in the 

 population of its other consumers, since many of them are also intensively 

 fished. It is more probable to assume that self-regulation of the 

 population occurs. The increase in the abundance of krill results in an 

 increase in the intensity of consumption of phytoplankton and a deteriora- 

 tion in the food supply for the individuals in the population. We can 

 assume that, as a result of this, a significant portion of the population 

 will go over, as in the southern waters where food is scarce, to a 

 four-year cycle. Later maturation will result in a decrease in the 

 population of the spawning pool. 



Since the crustaceans will live longer, they will drift further 

 north. The zone of their occurrence will expand, but, due to mechanical 

 factors, will remain within the Antarctic zone. Mackintosh has already 

 reported unusual northern occurrence of swarms of E. superba (1973). 

 The transportation of mature crustaceans outside the zone of optimal 

 conditions for the larvae may also lead to a decrease in the abundance 

 of this species. 



Spatial structure . The pelagic community has a certain spatial 

 structure, changing regularly with the course of the biologic seasons. 

 The nature of these changes can be considered on the example of the 

 three most numerous species of copepods-- Calanoides acutus , Calanus 

 propinquus and Rhincalanus gigas . During the biologic spring, all three 

 species are present as the overwintered population or, in the case 

 of the two former species, early juveniles of the new generation. During 

 this time, the core of the population of C_. acutus is located higher in 

 the water and its concentration is at its maximum. The core of C^. 

 propinquus is located more deeply, that of R^. g igas --deeper still. The 

 spread of the first of these three species may differ, that of the 

 second is always great. This structure results from the fact that C. 

 acutus rises to the surface and forms prespawning accumulations earlier 

 than C_. p ropinquus , and much earlier than _R. gigas . Later, when the 

 populations of all three species are in a more advanced state, ^. 

 propinquus with characteristic domination by egg-bearing females and the 

 first copepodite stages, for which the surface maximum is typical, takes 

 up the "feeding" position. At this time, the population of _C. acutus , 

 in which the second and third copepodites predominate and the fourth 

 copepodites are beginning to appear, begins to descend into the lower 

 layers of the epipelagic zone, while R. g igas , which has not yet completed 

 its spring migration, is still deeper than the other two species. At 

 the end of the vegetative season, C^. acutus almost completely leaves the 

 euphotic zone, R. gigas takes up the uppermost position, except in 

 regions where the sharp seasonal thermocline prevents them from rising. 

 In the last case C. prop inquus occupies the highest position (Voronina, 

 1972). ~ 



102 



