256 DISCOVERY REPORTS 



made at the time of marking. Even though the mark is found in the boilers, under 

 modern organization and speed of treatment of whale carcases, the position of capture 

 can usually be given within a radius of twenty miles or so, which can be accepted as 

 near enough for our purposes. 



The interest and attention given to these demands by all concerned, from the labourers 

 on the plan to the managers and directorates of the whaling companies, may once more 

 be mentioned, for the success of the work is wholly due to their cooperation and to 

 the care taken in rendering full and accurate returns. At an early stage of the experi- 

 ments it was found that some of the whalers wished to retain the mark as a memento, 

 and as stated on the form it is now sent to the finder after examination if he so desires. 



MOVEMENTS OF WHALES 



In plotting the movements of whales as indicated by the returned whale-marks, the 

 data available for each species have been arranged according to the length of time that 

 has elapsed between marking and capture. The marked whales taken during the same 

 season as that in which they were marked are referred to as the o-Group, those taken 

 the following season after an average lapse of one year as the i-Group, those after two 

 years as the 2-Group, and so on. Marked whales have also been captured in warmer 

 waters, in the region of the tropics, during the southern winter in the intervals between 

 the Antarctic whaling seasons. These are almost entirely Humpbacks, and they have 

 similarly been arranged in groups denoted as |-Group, i|-Group, and so on. The 

 ^-Group includes those marked in the southern summer and killed in the following 

 winter, the H-Group those killed in the next winter but one, and so on, the average 

 period between marking and capture being 6 months, 18 months, 30 months and so on. 



The positions of marking and capture are plotted on charts (Plates XLVI-LXVIII) ; 

 they are connected by straight lines as a matter of convenience. The lines, naturally, 

 are not intended to indicate the course taken by the whale after marking ; they do, 

 however, represent a resultant of these movements and are conveniently referred to as 

 tracks. The tracks of all the whales of each species taken during the same season as they 

 were marked (o-Group) are shown together on the same chart (Plates XLVI, XLVII, 

 LIII, LIV, LXII), although marks returned during five different seasons, 1932-33, 

 1934-38, contribute. Similarly, all the tracks given by the marks returned the first 

 season after marking are shown together (Plates XLVIII, XLIX, LV, LVI, LXIV), 

 and so on. In this way each chart gives a composite picture of the movements of whales 

 after a definite interval of time, but is derived from marking which extended ultimately 

 over five seasons. 



It will be convenient to consider the movements of the three species separately. 



MOVEMENTS OF BLUE WHALES 

 The total number of Blue whales estimated to be effectively marked is 668 and marks 

 have been returned from thirty-three of these whales. The majority of the returned 

 marks, namely eighteen, have been recovered the same season as they were fired. These 



