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1 . Baleen Whales 



Gambell (1973), Laws (1961, 1962, 1977a), Lockyer 

 (1972) , and Mackintosh (1942) noted that shifts in the 

 growth rates, pregnancy rates, and age at sexual maturity in 

 fin and blue whale populations had a high correlation with 

 whaling activities in the Southern Ocean. They interpreted 

 these changes to imply that whale stocks were food-limited 

 and perhaps close to maximum population levels before exploita- 

 tion. Under those conditions, growth may have been slowed 

 and sexual maturity delayed. Following whale stock decreases, 

 more krill would presumably have been available to surviving 

 whales, allowing growth and attainment of sexual maturity to 

 proceed faster (Figure 23). Hence, age at first reproduction 

 may be a historical index of the relative food availability 

 to some whale stocks. The authors speculated that unexploited 

 populations of krill consumers (e.g., fin whale stocks prior 

 to 1900) would likely increase until food-limited. These 

 arguments cast doubt on the premise that krill abundance is 

 so great that its predators could not be limited by its 

 availability. Instead, it seems reasonable that the aggregate 

 effects of krill competition could critically limit a variety 

 of krill predators. 



Mitchell (1974) discussed trophic relationships and 

 competition for food between baleen whales. Using distributions 

 and food preferences of North Atlantic whale populations, he 

 suggested that distribution and feeding patterns resulted 

 from food competition pressures. For example, fin whales 

 may restrict their feeding range, thereby avoiding direct 

 competition with blue, humpback, and minke whales by using 

 other foods. He felt that analagous situations also occur in 

 the Southern Ocean where sei whales benefited when decreased 

 blue and fin whale populations reduced competition for 

 krill. As evidence, he quoted Townsend (1935) who proposed 

 that following the reduction of southern right whales in 

 southern waters, sei whales extended their range to utilize 

 food resources previously unavailable to them due to the 

 presence of right whales. Mitchell also felt that other 

 whales in the Antarctic marine ecosystem may have exhibited 

 marked changes in their abundance and distribution following 

 whale harvest, and proposed the sei whales and minke whales 

 as the two species one could expect to show the greatest 

 density-dependent responses. Since sei whales were not 

 heavily exploited prior to the 1960 's, they may have increased 

 and extended their range into former blue and fin whale 

 feeding grounds. 



Minke whales, not harvested in earnest until 1971 and 

 originally sympatric with blue and fin whales in Antarctic 

 feeding grounds, might have exhibited even larger increases 



