238 DISCOVERY REPORTS 



whales. If the figures for a series of seasons, good as well as bad, were available, 

 the curves would probably show this increase. It is also possible that the corresponding 

 curves for Fin and Blue whales would take a similar form to the present curves for Sei 

 whales if data from bad seasons only, when whales and krill were scarce, were selected. 



In South African waters, on the other hand, where there is not usually any abundance 

 of large whales, the fatness curves for Sei whales approximate more closely to those for 

 Fin and Blue whales. They show a decrease in value as the season advances, although 

 they are already low when compared with the South Georgian figures. The greater 

 fatness of immature Sei whales when compared with adults, well shown by the figures, 

 is also found, to a much less extent, in Fin and Blue whales. This is shown in the 

 graphs given by Mackintosh and Wheeler (1929), where owing to its smaller promin- 

 ence it calls for no further comment than that the young whales appear to fatten 

 considerably towards the end of the season. This fatness of immature whales, which 

 occurs also in the Humpback, appears to be difficult to account for; it may be due 

 to recent suckling although none of the whales classed as immature were calves, and 

 when food was present in the stomachs it was the same as that of the fully mature ones. 



In Fig. 67 pregnant females are plotted separately, and as in Fin and Blue whales, 

 they are noticeably fatter than resting or lactating females. Lactating females are too 

 few in numbers for a curve of any value to be produced, but the isolated points show 

 that those measured were thinner than the average. Here again this species is in 

 agreement with the Fin and Blue whales. Data for South Africa are very scanty but it 

 is of interest to note that the only pregnant female measured was the thinnest whale of 

 the whole series, in sharp contrast with the Fin and Blue whales in which pregnant 

 females on the African coast are fatter than the pregnant females of corresponding 

 length at South Georgia. 



PARASITES 



EXTERNAL 



Large ectoparasites are very uncommon on Sei whales. Penella was found on only 

 six whales out of 141 examined for external parasites, three from South Africa and 

 three from South Georgia. Of the South African whales one carried two old Penella 

 stumps and two others adult Penella. Of the South Georgian whales two carried one 

 old stump each and the other four adult Penella in the region of the shoulder. 



Cirriped parasites are recorded from only one Sei whale, taken at Saldanha Bay. 

 A single specimen of Xenobalaniis globicipitis was found on the flank. 



Balaenophilus, on the other hand, commonly infests the baleen of Sei whales. It was 

 searched for in 116 whales at South Georgia and was found to be present in 100 and 

 absent in only sixteen, the infection varying from very slight to very heavy. Balaeno- 

 philus was looked for in only three whales at South Africa and was absent in one, but 

 heavy infections of the nauplius stage were present in two Sei whales at Durban. 



The ciliate protozoan Haematophagus, also, is commonly found on the baleen of Sei 

 whales. Of seventy-two whales at South Georgia which were examined for Haemato- 



