146 



R. M. LAWS 



may be drawn from these results; first, that the southern stocks of blue whales 

 have been decreasing for many years and are now at a very low level; 

 secondly that the southern stocks of fm whales are now decreasing and have 

 probably been progressively decreasing for several years at the very least. In 



I930 



1935 



1940 



1945 



1950 



1955 



I960 



Fig. 4. — Changes in the mean lengths and estimated percentage immature in antarctic 

 pelagic catches of blue and fm whales. 



the rest of this paper it is taken for granted that the stocks of fm and blue 

 whales are not increasing. 



CHANGES IN THE COMPOSITION OF THE CATCHES 



Detailed information on the catches of whales is given in the annual pubHca- 

 tions of the Bureau of International Whaling Statistics. This enables variations 

 in the composition of the catches to be followed year by year. 



