THE LENGTH/WEIGHT RELATIONSHIP 301 



is attached to this figure than for the fin whale estimate, it is very unUkely to be greatly in 



error. 



The average growth curves now obtained for different species are compared in Text-fig. 12, by 

 taking Lt^ as the origin of the curves. For the four Balaenopterids the slopes of the linear segments of 

 the growth curves have also been plotted against the slope of the logarithmic parts and are found to be 

 closely correlated; the steeper the linear segment, the steeper is the logarithmic segment. 



THE LENGTH/WEIGHT RELATIONSHIP 

 It has been shown that in the baleen whales growth in length is extremely rapid, probably following an 

 exponential curve in the second half of pregnancy. In general, IFccL^ so the growth in weight will 

 be even more rapid and it is therefore instructive to examine the data on the weights of whale foetuses. 

 Zemskiy (19506) gave records of foetal length and weight for sixty-five fin whale foetuses. Nishiwaki 

 and Hayashi (1950) plotted weight against length for forty-three fin and blue whale foetuses, but their 

 records were not given in tabular form and have not been used. Nishiwaki and Oye (1951) gave full 

 information on the weights and lengths of thirty-nine fin whale, and twenty-three blue whale foetuses, 

 and Symons (1955) gives the weight and length of one large blue whale foetus. The National Institute 

 of Oceanography has records of foetal weights for ninety-six fin whale, seven blue whale, nine hump- 

 back whale and three sei whale foetuses making, together with published records, a total of 243 baleen 

 whale foetuses for which length/weight records are available. All data have been converted to metric 

 units for comparison, and the 115 previously unpublished records of foetal weight obtained by the 

 National Institute of Oceanography are set out in Table 6. In addition Mohl-Hansen (1954) gives 

 records of weight and length for ninety-three porpoise foetuses. 



In Text-fig 13 this material is presented graphically. The records for blue, fin and sei whales were 

 originally plotted separately but showed no specific differences and have not therefore been distin- 

 guished The three rather lighter than average records are fin whales. The humpback whale foetuses 

 appear to be consistently heavier than blue, fin and sei whale foetuses of similar lengths and have 

 therefore been given separate symbols. The plotted points for the porpoise are monthly means. 



It is apparent that there is little scatter; the greater scatter at lower values is at least partly due to 

 the limits of accuracy of the methods of weighing, how much of the umbilical cord is included, etc. 

 For the genus Balaenoptera the range of variation in length between individuals of the same weight 

 isabout 20% of the mean length. , ., r c ui 



Zemskiy (1950^;) examined the relationship between foetal length and weight for 100 fin whale 

 foetuses (details of only sixty-five are given in his paper). He plotted weight against length on 

 arithmetic scales and concluded that 'the intra-uterine development of the fin whale embryo may be 

 divided into two stages having different features. The first period is characterized by an intensive 

 growth in the linear dimensions of the embryo while its mass increases relatively slowly. The rapid 

 growth in length continues until the embryo is approximately 90 cm long. The second period is 

 characterized by an intensive growth in weight whilst the linear growth of the embryo is relatively 

 slow' (translation). Adoption of logarithmic scales (Text-fig. 13) shows, however, that there is a 

 constant relation between weight and length at least from about 30 cm onwards. The decrease in the 

 embryonic length/weight ratio, K, used by Zemskiy is presumably only another way of expressing 

 the known fact that WazL\ so that weight naturally increases more rapidly than length. 



The mean lengths at birth for southern blue and fin and for northern sei whales are estimated to be 

 7.0, 6-4 and about 4-4 m., respectively. From the regression line fitted by inspection ^^ Text-fig. 13, 

 these lengths correspond to birth weights of 2500 kg. (2-46 tons), 1900 kg. (i-86 tons) and 650 kg. 



