464 DISCOVERY REPORTS 



We have then, 10 whales (all except one marked between 1934 and 1937) for which a minimum age 

 is known and for which data on the number of corpora in the ovaries are available. Particulars of 

 these whales are given in Table 30. What is it possible to say about these data? 



For these individuals the mean period between marking and recovery is 13-8 years (ranging from 

 2 to 24 years) and the mean number of corpora is 15-7 (ranging from 3 to 40). If fin whales are marked 

 on average at about the time of puberty (when corpora begin to accumulate) then these data suggest 

 the mean increment of corpora is likely to be about 1-14 per year. If, on the other hand, they tend to 

 be younger or older than this stage when marked, then the average annual increment of corpora is 

 likely to be respectively more or less than 1-14, with the reservations imposed by the small size of the 

 sample. (It is, however, interesting that the sample is equally divided between whales less than, or 

 more than 15 years from marking to recovery. The 'apparent' annual increment is the same in both 

 groups, namely 1*14.) 



There is some evidence bearing on the question of whether female fin whales are marked on average 

 before or after puberty. There are 24 female fin whales marked in the pre-war operations which were 

 recovered either in the same season (o-group) or a year later (1 -group), for which the lengths at recovery 

 were known (Rayner, 1940). The mean length at marking should be below the mean length (plus 

 2 s.E. of the mean) of the animals in this sample. It is known that the mean length of southern hemi- 

 sphere female fin whales at sexual maturity is 65-25 ±0-32 ft. (p. 407). The mean length of the o-group 

 and 1 -group sample is 65 -42 ±2- 18 ft. (mean and two standard errors), and this figure is probably 

 a little high. It is well known that length measurements made on floating factories tend to be slightly 

 higher than control measurements made by biologists, and the effect of the minimum length regulations 

 might be to exclude some of the smaller females from the o-group and 1 -group recoveries. It has 

 been shown that the average rate of growth at the period corresponding to these lengths is rapid, 

 amounting to some 3 ft. per year (p. 413), which has the effect of minimizing errors in estimating the 

 age at marking. It is, therefore, probable that the mean age of these whales at marking was a little 

 less than the mean age at puberty, say half a year, because the sample includes roughly equal numbers 

 of o-group and 1 -group females. The length variation (±2-18 ft.) corresponds to an age variation of 



