TOOTHED WHALES 289 



of August, which also agrees very well with this author's conclusions; peak calving is estimated as 

 the end of June and does not seriously conflict with the information given by him. 



Limited data are published by Vladykov (1944) and Doan and Douglas (1953) from studies of the 

 white whale in the Saint Lawrence area and Hudson Bay, respectively. These are set out in Text- 

 fig. 5 from which it appears that in this species also foetal growth can be described by a linear plot, 

 with parturition at the end of June and Lt^ in the middle of June, so that the estimate of (^1,-^0) is 

 1 2\ months, or 380 days. For gestation periods of this magnitude Lt^ is estimated to be o- 1 x (gestation 

 time). Then LtQ^{o-i x 38o)/o-9^42 days. The gestation period is therefore estimated to be 422 davs, 



100 





£ so 



I 

 I- 

 o 

 z 

 u 

 _l ^^-^ 



n I 1 1 —- — ^"^ — ' ^ 



D J F 



■*— *°-* MONTHS 



Text-fig. 4. Foetal growth in length of the porpoise, Phocaena phocoena. Black circles, monthly means, Denmark; 

 white circles, single records, Denmark ; white triangles, single records, Holland. 



ISO 



o 



100- 



I 

 I- 



z 

 u 



so 



MJJASONDJ F 



-t„_. 



M A M J J A 

 MONTHS 



Text-fig. 5. Foetal growth in length of the white whale, Delphinapterus leucas. 



or just under 14 months, with the majority of conceptions in April and May and birth at an average 

 length of 1-5 m. taking place about the end of June. This is not in close agreement with the tentative 

 conclusions of Vladykov (1944) and Doan and Douglas (1953). 



In the Greenland area this species has been studied by Degerbol and Nielsen (1930) who give 

 lengths of 131 foetuses measured in the 6 months, November to April. Their data also suggest that 

 after the initial period growth is linear, but the slope of their growth curve is steeper, and the neonatal 

 length evidently greater, than in the Canadian populations. It is not possible to estimate the gestation 

 period from these data. 



For these three species of toothed whales the foetal growth in length can be described by a linear 

 plot over most of the period of gestation and the estimates of the length of the gestation period by 

 means of Huggett and Widdas's (1951) method are in fairly close agreement with previously published 



