-104- 



in abundance. Moreover, minke whales rapidly reach sexual 

 maturity, have a relatively short calving interval (one or 

 two years), and feed in the Antarctic year-round. Thus, 

 minke whales may have been in an optimal position to benefit 

 from increased krill availability. Unfortunately, scant 

 information on almost all aspects of minke whale biology and 

 ecology precludes assessing the magnitude of any population 

 changes which have occurred. Estimates of "initial" minke 

 whale population levels are made with reference to the early 

 1970 's. Recent evidence presented to the International 

 Whaling Commission indicates that the age of sexual maturity 

 in minke whales has, over the past several decades, decreased 

 from 14 to 7 years (R. M. Laws, pers. comm. ) . If their 

 populations had increased following harvest of their krill 

 competitors, population increases might have begun decades 

 ago. Therefore, comments that minke whales have shown no 

 measurable increase in their abundance (Mackintosh, 1970) do 

 not take into account earlier ecosystem adjustments between 

 krill consumers. Minke whale population changes may well 

 have taken place before the first standing stock estimate of 

 the species was ever made. 



2 . Seals 



Seals which use krill may have responded to the baleen whale 

 decline also. Of the four true Antarctic seals, leopard and 

 crabeater seals depend most heavily on krill. Since crabeater 

 seals are the most abundant and depend almost completely on 

 krill, they may have shown the most marked response. Despite 

 reports that seal populations have not increased following 

 heavy whaling (Mackintosh, 1970) , Laws (1977a) presented 

 evidence that seal populations may indeed be increasing. He 

 stated that the age at first reproduction of crabeater seals 

 has been decreasing for the last several decades similarly 

 to fin and humpback whales (Figure 23). Laws attributed the 

 decrease in age of first reproduction to a decrease in the 

 competition for food resources, primarily krill. He also 

 cited evidence from the area west of the Antarctic Peninsula 

 which was a whaling sanctuary prior to 1955. When this area 

 was opened to whaling in 1955, stocks were rapidly depleted. 

 Crabeater seal reproductive material from that area showed 

 that age at first reproduction decreased from 4 years of age 

 in 1955 to 2 1/2 years of age in 1970. Laws interpreted 

 these data to suggest that the population had increased 

 during the last two decades as a result of diminished competition 

 with whale stocks for food. 



Southern fur seals may have increased due to whaling 

 (Laws, 1973, 1977a). Throughout the Southern fur seals' 

 Antarctic range, slow population comebacks have occurred 



