370 DISCOVERY REPORTS 



takes place only within the first two or three years after marking. For example it is not impossible 

 that the discomfort or shock of a whale mark causes some whales to shift their ground, but perhaps 

 a more likely explanation is that it is only the younger, more adventurous whales which normally 

 wander to other longitudes. Many of the short-term marks do show wide dispersal, and it can be 

 supposed that where long-term marks show dispersal the whale was young at the time of marking, 

 that dispersal took place soon afterwards, and that the whale then settled down in limited territory 

 and thereafter kept to the same annual migration route. Whales which show little or no dispersal 

 may be those which were marked at a comparatively advanced age when their habits may be supposed 

 to have already become fixed. 



There is, however, little evidence to say whether or not this is the correct explanation, and, in 

 view of the small number of marks returned, it must be remembered that the extremes of dispersal 

 shown by the short-term marks are liable to large chance variations. 



DISPERSAL IN BLUE WHALES 

 Fifty marks have now been returned from forty-five Blue whales, all from known positions. Twelve 

 recoveries have been made since Rayner's report was published, and there are now recoveries in 

 nine year-groups (Table 3). No marks have been returned in 6-group to 10-group inclusive. Details 

 of the sex of the whale and its length when captured have been recorded for twenty-eight of the 

 recoveries, eight males and twenty females. No recoveries of marked Blue whales have yet been 

 made outside the Antarctic. 



Table 3 . Marked Blue whales killed in each group 

 (See note, p. 377) 



The tracks of all these whales are shown in Fig. 12; fourteen of the marks were recovered in 

 Area II and thirty-one in Areas III and IV. Two almost vertical tracks are seen, and these represent 

 whales taken in almost the same longitude as that in which they were marked (Mark No. 859 near 

 35 W, and No. 8743 near 30 E). The other recoveries show greater or lesser degrees of dispersal. 

 If this chart is compared with the time-charts for Fin whales (Figs. 2, 3 and 4) it can hardly be 

 doubted that a higher proportion of Blue than of Fin whales has dispersed, but as in Fin whales 

 the slopes of the tracks generally show more rapid dispersal among the short-term recoveries than 

 among the long-term recoveries. Some whales have crossed the border both ways between Areas III 

 and IV, but not one has crossed between Areas II and III. 



As with Fin whales, from the positions of marking and recovery of marked whales, the range of 

 longitude over which Blue whales are known to disperse can be examined. Four Blue whales have 



