260 JOHAN T. RUUD 



males. The mean mortality rate for the period 1947/48 through 1952/53 is 0-22 for 

 females and 0-34 for males, with 0-28 as an average for both sexes. It should be 

 borne in mind that this is either the true mortality rate, or, what is more likely, it is 

 too low. 



It is assumed that the female fin whale has her first pregnancy at an age of 3 or 

 4 years, and that she gives birth to one calf every second year. The maximum rate of 

 increase for the stocks of fin whales should thus be 0-25 per adult per year. We know 

 nothing about the annual mortahty rates of immature age groups, but most hkely 

 they are considerable, because some will be taken in whaUng operations (compare 

 the left limb of the age distribution curves). It must be assumed, therefore, that the 

 real rate of increase for the whole stock of fin whales must be significantly lower 

 than 0-25 per year. 



Since the annual mortality rate calculated above was 0-28 or more, the inevitable 

 conclusion is that the Antarctic stocks of fin whales were overfished in the period 

 1946/47 through 1952/53. In that period the annual catches were about 21 thousand 

 fin whales. In subsequent seasons they have increased to more than 27 thousand fin 

 whales per year. Unless the stocks have increased, this means increased mortahty 

 rates also, and the stocks are being heavily overfished. 



REFERENCES 



Baranov, F. I. (1918), On the question of the biological foundation of fisheries. Bull. Bur. Fish., 



Petrograd, 1 (1), 81-128. 

 EscHRiCHT, D. P., and Reinhardt, J. (1866), On the Greenland right whale. In: Recent memoirs 



of the Cetacea, London, 1-143. 

 Ruud, Johan T. (1940), The surface structure of the baleen plates as a possible clue to age in whales. 



Hvalradets Skrift. 23, 1-24. 

 RinjD, Johan T. i[1945). Further studies on the structure of the baleen plates and their application 



to age determination. Hvalradets Skrift. 29, 1-69. 

 Ruud, Johan T., and Jonsgard, Age (1950), Age studies on blue whales taken in Antarctic seasons 



1945-46, 1946-47 and 1947^8. Hvalradets Skrift. 33, 1-66. 

 ScoRESBY, W., Jr. (1820), An account of the Arctic regions. Edinburgh, 1. 

 ToMiLiN, A. G. (1945), The age of whales as determined from their baleen apparatus. C.R. Acad. 



Sci., U.S.S.R., 49 (6), 460-463. 



