. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 426 DISCOVERY REPORTS Table 17. Estimated frequency of conceptions in multiparous southern hemisphere fin whales, based on 694 records of foetal length Conceptions Period No. Percentage January/February 0 o-o February/March 0 o-o March/April 20 2-9 April/May 164 23-6 May/June 191 27-5 June/July 131 18-8 July/August 63 9-1 August/September 5° 7-2 September/October 34 4-9 October/November 24 3-6 November/December 13 i-8 December/January 4 o-6 Total 694 ioo-o. MONTHS Text-fig. 43. Monthly percentag
. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. 426 DISCOVERY REPORTS Table 17. Estimated frequency of conceptions in multiparous southern hemisphere fin whales, based on 694 records of foetal length Conceptions Period No. Percentage January/February 0 o-o February/March 0 o-o March/April 20 2-9 April/May 164 23-6 May/June 191 27-5 June/July 131 18-8 July/August 63 9-1 August/September 5° 7-2 September/October 34 4-9 October/November 24 3-6 November/December 13 i-8 December/January 4 o-6 Total 694 ioo-o. MONTHS Text-fig. 43. Monthly percentage frequency of pairing (full line) and calving (broken line) of 694 multiparous females (with 3 or more corpora in the ovaries). and shown graphically in Text-fig. 43. The peak pairing season is from April to July, as opposed to May to September in primiparous females, and the mean date of conception for multiparous females (20 June), is a month in advance of the estimated mean date of conception for primiparous females (21/22 July). The multiparous curve is skewed with a long 'tail' from July to December, whereas the primiparous curve is much more symmetrical about the mean, so it is better to compare the median dates. The median pairing of multiparous females (8 June) is then seen to be about 6 weeks in advance of the median date for primiparous females (21 July). It should also be pointed out that the beginning of the steep rise in the multiparous curve of conceptions is actually about half a month later, that is to say in May, if half-monthly periods are considered. Of the 164 foetuses estimated to have been con- ceived between 12 April and 11 May, 98 were conceived in the second half of the period, so that only about 90 foetuses were conceived earlier than the beginning of May. These amount to about 13% of all multiparous conceptions. Evidence given above suggests that the majority of females, if not all, experience a monoestrous cycle in their first sexual season. There
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