DISPERSAL IN FIN WHALES 367 



The range of dispersal and the proportion of whales found to have dispersed after various periods 

 can be demonstrated (so far as the data allow) by histograms, as in Figs. 7-1 1. Dispersal is measured 

 horizontally in units of 5 of longitude. Thus a whale which has moved, say, 2° 50' west of the position 

 of marking will be in the 0-5 W unit, or one moving 17 east will be in the 15-20 E unit. At the 

 centre of the scale o° is not, of course, the Greenwich meridian; it is any marking position, taken 

 as the zero point from which any whale has eventually moved a certain number of degrees east or 

 west. 



Range of dispersal. Simply to show the maximum range of dispersal it is not strictly necessary to 

 apply a correction for the distribution of catches. Fig. 7 shows the total actual numbers of Fin whales 

 marked in Areas II and III, and recovered at different distances east or west of the longitude of 

 marking. (The number of Area IV marks recovered was insignificant.) It is seen that a larger 

 proportion of the marked whales in Area II has been recovered within io° of the longitude of 

 marking than in Area III. It has to be noted, however, that practically no whaling is carried out in 

 Area I 1 and no marks can be returned from this area; knowledge of the westward dispersal of whales 

 marked in Area II is therefore limited to those recovered east of 6o° W, the western boundary of the 

 area. This is probably the explanation of the fact that only one whale marked in Area II has dispersed 

 more than 20 westwards, whereas in Area III a number of whales has done so. It is interesting to 

 note, however, that no whale marked in Area III has moved over a greater distance than 40 westwards, 

 even though a whale marked on the extreme western boundary of Area III could travel up to 6o° 

 westwards (to the western boundary of Area II) and still be recovered, as whaling takes place regularly 

 as far as 6o° W. 



Dispersal eastwards of Fin whales marked in Area II does not extend more than 50 , two whales 

 having moved up to this distance. As whaling takes place regularly in Area III, and in most seasons 

 throughout most of Area IV, it is apparent that a whale marked on the eastern boundary of Area II 

 could be recovered after dispersing over a much greater distance than this. The same thing applies 

 to a less extent in Area III where one whale has moved up to 45 eastwards, although recoveries are 

 possible in Areas IV and V. 



It seems, therefore, that there may be a limit to the range of dispersal in Fin whales, although the 

 relatively small number of marks recovered must be remembered in drawing such conclusions. 



Dispersal in time. Fig. 8 shows the actual recoveries of marked Fin whales in all Areas, and in 

 Fig. 9 the same data are used but corrected according to the catches in each io° sector. The correction 

 has been applied as follows. Since there is a greater chance of marked whales being recovered in 

 sectors where catches are high, in any one season the recovery of a marked whale from a sector in 

 which small catches have been made will have more significance in the measurement of range and 

 rate of dispersal, than a recovery from a sector in which catches are large. To allow for this the 

 number of recoveries of marked whales in each io° sector in a particular season has been multiplied 

 by a coefficient obtained by dividing the average catch for all sectors for that season by the actual 

 catch for each sector in turn. (This coefficient will be small for a sector where a big catch has been 

 made, and large for a sector where a small catch was taken.) 



Since rather small numbers of marks are recovered in each season after the first few seasons 

 following marking, separate histograms are shown in Figs. 8 and 9, not for each year-group but for 

 series of three-year-groups. In each of these groups the extreme range of dispersal is included in 

 the figures. In Figs. 10 and 11 the short-term recoveries (0-2 groups) are similarly compared with 

 all the later recoveries (3-17 groups), but the figures are expressed as the percentage of the total in 

 each assembly of groups. 



1 In seasons 1938-39 and 1950-51 there was some whaling between 60-70° W. 



