THE AGE OF FEMALE BLUE WHALES 



265 



stock. Ultimately the population may be so reduced as to make recovery impossible or 

 at best very slow. 



The number of Blue whales taken in Antarctic whaling, including South Georgia, 

 since the beginning, as far as known, are given in a list in Appendix I. 



AVERAGE LENGTH OF BLUE FEMALES 



Hjort, Ruud and Lie have, in their analyses of the pelagic catch for the last five years, 

 computed the average length of whales taken. The following table is from Hvalrddets 

 Skrifter, No. 14, p. 28: 



The writers say: "This summary shows that the average length in each group is 



practically the same for four seasons But there is no real evidence of any continuous 



decline in the average length either of mature or immature animals" (No. 12, p. 24). 



Prior to this table the authors have drawn attention to a general principle that "all 

 experience gained in fishery and whaling investigations goes to prove that the influence 

 of fishing or whaling operations upon the stock first becomes noticeable in a reduction 

 of the size of the older animals" (loc. cit., p. 22). 



In a note to Nature (1936) I drew attention to a fallacy underlying this presentation 

 of mean lengths. The authors have divided the whales taken into two categories, mature 

 and immature, and calculated the mean length of the whales in each. The possible effect 

 of whaling is therefore masked, since no account is taken of the proportion of mature and 

 immature whales in the catch. 



I have calculated the average length of the whole catch of females in each of the above 

 five seasons without dividing them into mature and immature classes. The necessary 

 data has been culled from the Hvalrddets Skrifter, so that the basis of argument is the 

 same as that of Hjort, Ruud and Lie. The average lengths are shown in the following table : 



6-2 



