Discovery reports (1962) Discovery reports discoveryreports31inst Year: 1962 475 AGE-DETERMINATION BY MEANS OF THE OVARIAN CORPORA is calculated as before to be 857 indicating a total immature mortality from birth to 5 years of about 53'3> a verY similar result to that given by the time specific method. This apparent survival curve again approximates to the diagonal type (Text-fig. 59). Mortality appears to be higher in the early segment of the curve and increases again after 25-26 years. Between 9 and 26 years the survival curve plotted on a logarithmic scale is almost exactly linear, th
Discovery reports (1962) Discovery reports discoveryreports31inst Year: 1962 475 AGE-DETERMINATION BY MEANS OF THE OVARIAN CORPORA is calculated as before to be 857 indicating a total immature mortality from birth to 5 years of about 53'3> a verY similar result to that given by the time specific method. This apparent survival curve again approximates to the diagonal type (Text-fig. 59). Mortality appears to be higher in the early segment of the curve and increases again after 25-26 years. Between 9 and 26 years the survival curve plotted on a logarithmic scale is almost exactly linear, that is to say the decline in numbers is exponential. For this segment of the curve the apparent rate is e 00973 or 90-8, corresponding to an annual mortality rate of 9-2. One of the central problems of whale research is to define and distinguish the different populations being sampled; a complementary problem concerns the extent to which the samples from the catches are representative of the actual population in the sea. Until more progress is made in the solution of these problems it would seem that population studies will lack precision. 1000 500 100 a. o > > a m 20 30 AGE IN YEARS Text-fig. 59. Dynamic survival curve for female fin whales. See text for method of construction. Growth curves The relation between length and corpora number for area 11 females has already been discussed (Table 6, Text-fig. 25). The average length at physical maturity was there taken to be 73 ft., which was the average length of 187 females which had more than 20 corpora in the ovaries. Nishiwaki, Ichihara and Osumi (1958) suggest that after the attainment of physical maturity there is a slight decrease in body length and the present material also suggests this, although the shrinkage is evidently slight and there is no statistical support for it. The relative growth curve in Text-fig. 25 was, therefore, fitted to the average lengths at different corpora numbers so that it attained 73 ft.
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