i66 AGE JONSGArD 



exploited selectively to a great extent, since the percentage of sexually mature 

 animals in the catches has always been very much less than what it must be 

 in the normal stock at large. Females apparently attain maturity and become 

 pregnant for the first time at an age of two years, and they give birth to one 

 calf every year from the third onwards. The sex ratio is approximately 

 50 : 50. Thus the number of calves born any one year is equal to 50 per cent of 

 the mature stock, animals in their first mature year excluded. An accumulated 

 stock will consist, therefore, of approximately 60 per cent sexually mature 

 animals, and this result will be only shghtly influenced by mortality. 



In the catches taken over a period of twenty-one years, from 1938 to 1958, 

 the percentage of mature animals has varied between 18*3 and 43*2, the 

 average for all seasons being 35-0 per cent, about 25 per cent below the 

 approximate figure calculated for the normal stable stock. Thus, immature 

 animals have been exposed to a much higher rate of exploitation than have 

 the mature ones. 



The net result must be a reduction in the total stock and a corresponding 

 decrease in the abundance of whales in the whaling fields. The chances for a 

 continuation of the highly selective catch will be reduced correspondingly 

 if the total catch is to remain the same. 



The significance of an increase in the relative number of mature animals 

 in the catches is, therefore, in this case that the stocks of whales have been 

 reduced appreciably. 



SUMMARY 



In Norway the catching of minke whales started about thirty-five years 

 ago. Since 1938 a licence has been required for minke whaling, and since 

 then statistical information has been collected which includes position and 

 date, as well as numbers, sex and size of all animals caught. 



Investigations of the minke w^hale in post-war years have given relatively 

 good information as regards its biology in general. We are not, however, 

 able to determine individual age in this species. 



A characteristic feature relating to the catch of minke whale is that all 

 animals met with are being hunted. No limitation by minimum length exists. 



The catch per unit of effort has shown no sign of depletion up to 1958, 

 but in 1959 there was a marked decline. 



In spite of the fact that the total catch has increased, the number of smaller 

 calves taken has decreased since 1949. We assume that this is due to failing 

 recruitment, but other possibilities are also discussed. 



The composition of the catches has shown great changes with regard to 

 the percentage of mature animals during the period 1938-58. It can be 

 demonstrated that the changes occurring during the period 1938-53 are due 



