EFFECTS OF WHALING ON BALEEN WHALES 139 



The end of the whahng season in post-war years has been dependent on the 

 attainment of the catch quota, and in recent years owing to the increasing 

 intensity of the whaling operations the length of the whaling season has been 

 only sixty-nine days for fin whales and forty-four days for blue whales. In 

 1932-3 the duration of the season was 177 days. 



(4) In an industry like whaling protection is best achieved by restricting the 

 catch to an annual quota. With the exception of the earlier voluntary agree- 

 ments no overall quota was fixed until the 1946 Convention adopted a figure 

 of 16,000 blue whale units which first came into operation in the 1947-8 

 season. This unit is based on oil yield ; one blue whale is considered equal to 

 two fin, two and a half humpbacks or six sei whales (Balaenoptera borealis 

 Lesson). The quota has subsequently varied between 16,000 and 14,500 

 B.W.U. (Fig. i) composed of these four species. 



(5) By the 1937 agreement a sanctuary area was declared in the Pacific Sector 

 from 70° W to 160° W. Virtually no whaling occurred in this extensive 

 region until the 1955-6 season when it was opened to whaling in an attempt 

 to reduce the pressure on the stocks of whales in other sectors. Pelagic 

 whaling is forbidden in the southern hemisphere north of 40° S latitude. 



The other provisions of these agreements do not concern us here. 



(c) Geographical segregation 



For obvious reasons research on the southern stocks of fm and blue whales 

 has been virtually confmed to the populations present on the antarctic 

 whaling grounds in the summer months. 



We may safely assume that there is a negligible interchange between the 

 stocks in the northern and southern hemispheres. It has long been known 

 that there is also a segregation of the antarctic stocks of baleen whales into 

 more or less separate geographical groups. The results of whale marking 

 show that the distribution is not random and that many fm whales return 

 after their migrations year after year to the place of marking (Mackintosh, 

 1942; Brown, 1954)- Hjort, Lie & Ruud (1932) divided the antarctic whaling 

 grounds into five areas (I-V) based on the distribution of catches, mainly of 

 blue whales, by Norwegian factory ships. In subsequent papers they con- 

 firmed the value of this division. Mackintosh (1942) examined the distribution 

 of blue, fm and humpback whales and suggested the extension of area I ; he 

 also proposed a new area VI to include the rest of the Pacific sector. This 

 terminology is in general use by whale biologists and by the Bureau of 

 International Whaling Statistics, but it was based largely on the distribution 

 of the catches of blue whales, which in pre-war years was the most important 

 species. Since 1945 the fm whale has been the most important species and 

 the post-war distribution of the catches suggests that the whaling areas I-VI 



