138 R. M. LAWS 



(a) Sampling the catch 



Some twenty factory ships with their attendant catchers operate in the area 

 of ocean between the Antarctic Convergence and the ice-edge which is 

 some 8-9 million square miles in extent during the whaling season (Mackin- 

 tosh & Brown, 1956). Whaling is a skilled occupation and searching for 

 whales plays an important part. It is not possible to collect a sample of intact 

 whales, as with small animals, nor to examine the catch at the end of the 

 voyage as fisheries biologists often can, for whales are large and are rapidly 

 dismembered and processed after being hauled aboard the factory ship. 

 Sampling opportunities are therefore limited and material for age determina- 

 tion must be collected during the operations on deck. 



Much effort has gone into fmding methods of age determination and 

 three complementary methods are available, based on corpora albicantia in 

 the ovaries (Laws, 1958), ridges on baleen plates (Ruud, 1945), and lamina- 

 tions in the ear plug (Purves, 1955). Owing to the great size variation and 

 the fact that growth, though initially very rapid, slows down or ceases at a 

 relatively early age, length measurements have been useful for population 

 studies only in a very general way. 



(b) Varying restrictions on whaling activities 



Prior to the 1932-3 season antarctic pelagic whaling was unrestricted though 

 whaling from land stations was regulated. Various voluntary agreements, 

 national laws and regulations relating to whaling were introduced, notably 

 by Norway and the U.K., but with the development of pelagic whaling only 

 international measures were adequate for its control. A number of inter- 

 national agreements were concluded, namely the Convention of 193 1, the 

 agreements of 1937 and 1938 and the International Whaling Convention of 

 1946 which is at present in force. I propose briefly to summarize the more 

 important restrictions affecting the catches of blue and fm whales : 

 (i) The taking of lactating females and suckling calves is prohibited. 



(2) Minimum length regulations mean that the younger animals in the stocks 

 are absent or under-represented in the. catches. The minimum length for 

 blue whales was in the earlier seasons 6$ ft, increasing to 70 ft in 1937-8. 

 For fm whales it was increased from 55 to 60 ft in 195 1-2 and reduced to 

 57 ft in 1954-5 (Fig. 4). 



(3) There have been successive changes in the opening date of the pelagic 

 whaling season, from 20th October in 1932-3 to 7th January in the five 

 seasons up to 1958-9. The opening date for blue whales was postponed to 

 i6th January in 1953-4, to 21st January in 1954-5 and to ist February in 

 1955-6. This was designed to afford more protection to the blue whale. 



