. I960 Text-fig. 54. Antarctic catches of fin whales from 1909/10 to 1957/58 according to the whaling areas. had fallen to 32%. This season was rather an abnormal one and the sample may have been less representative of the stock than in later seasons, but bearing in mind the additional evidence from blue whales, it does seem reasonable to conclude that the real pregnancy rate was low. By 1950/51, after several seasons of sustained heavy exploitation (Text-fig. 54), the 'percentage pregnant' was above 80%. This would appear to be the maximal response of which the fin whale was capable, for in l
. I960 Text-fig. 54. Antarctic catches of fin whales from 1909/10 to 1957/58 according to the whaling areas. had fallen to 32%. This season was rather an abnormal one and the sample may have been less representative of the stock than in later seasons, but bearing in mind the additional evidence from blue whales, it does seem reasonable to conclude that the real pregnancy rate was low. By 1950/51, after several seasons of sustained heavy exploitation (Text-fig. 54), the 'percentage pregnant' was above 80%. This would appear to be the maximal response of which the fin whale was capable, for in later seasons (1955/56-1958/59) even after larger catches the percentage pregnant was stable at about 80%. The apparent decrease in the pregnancy rate in 1958/59 is disturbing, but may not be real, and it is too early to assess its full significance. Owing to differential sampling as mentioned above, a 'pregnancy rate' of 80% is probably equivalent to a real pregnancy rate of about 60%. Similarly in areas in and iv the 'pregnancy rate' appears to have stabilized in post-war years at rather more than 80%. A very small sample from area m in 1932/33 suggests a very much lower pregnancy rate, but little confidence can be attached to this figure. In area 1 the ' percentage pregnant' was round about 70-80% from 1955-58 when very large catches were being made in this area. Area I was a sanctuary up to 1955/56, so that according to the hypothesis that fertility is lower in natural conditions and rises with increasing fishing mortality, the ' percentage
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