. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 4°4 DISCOVERY REPORTS It has already been shown that the duration of the gestation period is about n| months. A curve showing the seasonal distribution of calving has, therefore, been constructed by advancing the curve of conceptions by 3 weeks (Text-fig. 31). So far we have been concerned with the pairing season averaged from data collected over a number of years. It would be interesting to know the possible variation in the timing of the pairing season from year to Text-fig. 31. Monthly
. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 4°4 DISCOVERY REPORTS It has already been shown that the duration of the gestation period is about n| months. A curve showing the seasonal distribution of calving has, therefore, been constructed by advancing the curve of conceptions by 3 weeks (Text-fig. 31). So far we have been concerned with the pairing season averaged from data collected over a number of years. It would be interesting to know the possible variation in the timing of the pairing season from year to Text-fig. 31. Monthly percentage frequency of pairing (full line) and calving (broken line) of 956 pregnant females. Table 11. Estimated frequency of conceptions in southern hemisphere fin whales, based on 956 records of foetal length Conceptions Monthly period No. Percentage January/February 0 0 February/March 1 o-i March/April 23 2-4 April/May 196 20-5 May/June 249 26-0 June/July 180 18-8 July/August 116 I2-I August/September 81 8-5 September/October 52 5-4 October/November 36 3-8 November/December 17 i-8 December/January 5 °'5 Total 956 99-9 Our material collected by biologists is inadequate for this purpose, but there is information on foetal lengths of fin whales in the International Whaling Statistics covering the period 1925-58 and comprising many thousands of records. These measurements are not as accurate as those made by biologists which were used to elucidate the curve of foetal growth and the average pairing season. As Brinkmann (1948) has pointed out, small foetuses tend to be missed so that in the earlier months the mean foetal lengths given in the International Whaling Statistics are higher than expected in a true sample. However, we are interested in relative differences from year to year and the absolute lengths are not important in this connexion. In Text-fig. 32 the mean monthly foetal lengths given in the International Whaling Statistics have been converted from feet to metres
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