REPRODUCTION, GROWTH AND AGE 

 OF SOUTHERN FIN WHALES 



By R. M. Laws 



(Plates IV-VII and Text-figs. 1-60) 



GENERAL CONSIDERATIONS 

 Introduction 



In his paper on the southern stocks of whalebone whales, Mackintosh (1942) summarized the work 

 which had then been published and discussed some additional unpublished data. He remarked 

 that ' In recent years a good deal of new material relating to the breeding, growth, and age of whales 

 has been collected by members of the Discovery Committee's staff and other biologists who have 

 sailed in factory ships to the Antarctic. Work on this material, which includes records of large numbers 

 of ovaries, has been interrupted by the war, but it is hoped that it will be resumed in the future and 

 much progress should be revealed when the results are available' (p. 216); and later (p. 226), 'The 

 most important problem is to ascertain how many corpora lutea on the average are added each year 

 in a sexually mature female '. Annual collections of ovaries were initiated, and have been continued, 

 as a means of comparing the relative condition of the stocks of whales from year to year. A great deal 

 of extra material has, therefore, accumulated since 1942 and continues to increase yearly. In a series 

 of papers (Mackintosh and Wheeler, 1929; Wheeler, 1930; Wheeler, 1934; Peters, 1939; Mackintosh, 

 1942) attention was drawn to the use of counts of the corpora lutea and corpora albicantia in fin-whale 

 ovaries as a measure of age. Ovarian scars have also been used for determining age in other groups 

 of animals, for instance seals (Bertram, 1940; McLaren, 1958; Mansfield, 1958), the cow (Dawson, 

 1958), birds (Maynard, 1888; Wynne-Edwards, 1939), and even insects (Bertram and Samarawic- 

 krema, 1958). Several estimates of the annual rate of accumulation of corpora albicantia in fin whales 

 have been published ranging from 0-9 (Peters, 1939) to 2-5 (Wheeler, 1934), but they do not stand 

 up to detailed criticism. When the present investigation began the main objects were to establish to 

 what extent corpora albicantia persist in the fin-whale ovaries, and to determine the average annual 

 increment of corpora and the range of variation, so that they might be used to estimate the age of 

 whales. There are also many reasons why a better knowledge is needed of the whole breeding cycle 

 of fin whales and other species. It is of intrinsic biological interest and it has an important bearing 

 on population dynamics and on practical problems arising from the regulation of whaling. 



Two main approaches to the solution of these problems have been made. One is by way of a 

 detailed study of the gross and microscopic anatomy of the ovaries. The other is by investigation of 

 the annual reproductive cycle of the species. These are dealt with in the two main parts of this paper. 

 My own interest in this work began when I spent the antarctic whaling season 1953/54 on board 

 the floating factory ' Balaena ', and the time has come to present the results of this recent work 

 although new material continues to arrive. One considerable disadvantage is that it has still not been 

 possible to study the breeding biology of fin whales directly, in the breeding areas. In fact we still 

 do not know with certainty the location of these areas, though we may confidently assume that they 

 lie in the tropical and subtropical zones of the oceans. Even if the breeding herds were located it is 



