476 DISCOVERY REPORTS 



In Text-fig. 60 these length-at-age data are plotted. In addition the estimated mean length at 

 puberty (65-25 ft. at 5 years) and the estimated mean length at weaning (39 ft. at 7 months) are shown. 

 The pre-natal growth is known from the previous studies (Laws, 1959 a; and above, Text-fig. 30). 

 Conception is taken to be 0-93 years before birth. 



Table 33. Length-at-age data for female fin whales {see text) 



The von Bertalanffy equation (von Bertalanffy, 1938; Beverton and Holt, 1957) has been fitted to 

 the length-at-age data for mature females in area 11 (Table 33), 5J years and over, obtained from the 

 smoothed curve showing average lengths at different corpora numbers. This gives a theoretical curve 

 in which l t = L co (i — e~ kU ~' o) ), and a good fit is obtained for values at estimated ages above 5 years. 

 It is shown in Text-fig. 60 as a continuous line for which L x = 73-0 ft., K = 0-450, and t = 0-368. 

 The parameter t is the post-conception age in years. This theoretical curve has been extrapolated 

 backwards to t = 3-93, that is equivalent to a post-natal age of 3 years. 



80 

 ^ 70- 



h- 

 UJ 



S 60 



x 50 



i 40 

 ui 



_i 



30 

 > 

 o 



o 20 



10 



PHYSICAL MATURITY 



-O O— — O 1 I o- 



PUBERTY, 



l t =73O(j-e" 0450(, " 0368) ) 



^WEANING 



BIRTH 



■25-0 



UJ 



2000c 



ui 



150 x 



y- 

 O 



s 



100 -J 



> 



o 



5-0 * 



I 2 3 4 5 6 7 8 9 IO II 12 13 14 15 >I5 



AGE IN YEARS 



Text-fig. 60. Length-at-age curve for female fin whales, Antarctic area II. 



This growth curve has been completed by inserting the foetal growth curve already obtained, with 

 a mean neo-natal length of 20-8 ft. This leaves the segment of the curve from birth to 3 years to be 

 completed, but we have an approximate value for the length at weaning (39 ft. ; Mackintosh and 

 Wheeler, 1929), and the age at weaning has been established as about 7 months (p. 445). This has 

 been used to complete the growth curve and agrees quite well with expectation. The equation 



