The Constitution of Whale Populations in the Antarctic

II. Fin Whale

Abstract

The present account deals with the results of direct observations on the fin whales brought into the floating factory “Kyokuyo-maru” during the Antarctic season 1938/39 in the whaling ground so-called Area IV. During the period extending from 16th November 1938 to 14th March 1939, a total of 352 fin whales was examined.
(1) The average number of corpora lutea of 133 female whales (the average length of, which was measured 21.70m) was 11.36 (Tab. 7). It was seen from this that female fin whales averaged the same age during the 1925/26 season at South Georgia and during the 1938/39 season in the Antarctic Area IV.
(2) Of 12 whales with only one corpus luteum 5 were pregnant, 1 was lactating and 2 were ovulating or pregnant. Thus at least 6 (50%) whales would be estimated as they were pregnant in the first breading season and nearly the same results were obtained also in the whales with two or three corpora 1utea and 9 whales out of 133 whales examined were found to be ovulating or pregnant. But no whales with multiple ovulations were observed, although there were found one twins and one triplets. Furthermore, the peaks of the frequency graph ?? of the number of corpora lutea (Fig. 3), were more sparsely distributed than those of blue whales. From these facts, it might be safely concluded that the number of unfertilized ovu-lations before pregnancy must be more in number than that of blue whales.
(3) The apparent constitution of the stock i.e. the ratios of the different classes of whales examined might be summarized and compared with the results given by M_ACKINTOSH and W_HEELER (1929) at South Georgia as shown in the above table.
(4) Assuming that the onset of physical maturity in fin females coincides with the accu-mulation of 15 corpora lutea as was suggested by W_HEELER (1930), the proportion of the phy-sically mature females was found to be 40% of the sexually mature females and 24% of the total females.