Discovery reports (1929) Discovery reports discoveryreports21931inst Year: 1929 AGE EVIDENCE FROM CORPORA LUTEA 417 From the mature females of 1929-30 there are forty in which the age can be deter- mined in this way. Thirty-five of these belong definitely to the first or second year from sexual maturity, they constitute Group I of the frequency graph, and five are definitely in their third year (Group II). Now there are fifty-two whales with one, two, three or four corpora lutea (Group I) in the frequency graph (Fig. 3). Thus the overlap from Group II is seventeen, of which five have al
Discovery reports (1929) Discovery reports discoveryreports21931inst Year: 1929 AGE EVIDENCE FROM CORPORA LUTEA 417 From the mature females of 1929-30 there are forty in which the age can be deter- mined in this way. Thirty-five of these belong definitely to the first or second year from sexual maturity, they constitute Group I of the frequency graph, and five are definitely in their third year (Group II). Now there are fifty-two whales with one, two, three or four corpora lutea (Group I) in the frequency graph (Fig. 3). Thus the overlap from Group II is seventeen, of which five have already been traced. 5 10 NUMBER OF CORPORA LUTEA Fig. 5. Fin whales, females. Frequency of numbers of corpora lutea. All records from South Georgia since 1924-5. CORRELATION OF PHYSICAL MATURITY DATA WITH AGE EVIDENCE FROM CORPORA LUTEA In Fig. 3 the physically immature whales are distinguished from the mature, and it is evident that the change takes place between Groups III and IV. Therefore female Fin whales become physically mature between four and six years after sexual maturity, that is, between six and eight years from birth. Although this early maturity agrees with the very rapid bodily growth that is known to occur before sexual maturity, it does not suggest very long life. Whether the length of life can ever be more than a subject for speculation is doubtful and, perhaps, for economic purposes the knowledge is not necessary. At least one whale caught this season had attained the age of twenty years (No. 2815), if the average increase in the number of corpora lutea every two years is taken as four. No sign of a climacteric or diminution of fecundity appeared in the ovaries of any whale, not even in those of the whale men- tioned above which possessed forty-six corpora lutea. Nevertheless the largest size and greatest weight of ovary was found in whales with eighteen to twenty corpora lutea, which indicates that after about ten years the reproductive prime is over.
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