DISCUSSION 



G. SuRTEES : Is there any evidence that there is a significant difference in 

 the percentage of mature but unfertihzed females in unexploited and 

 exploited whale populations ? Is there any change in sex ratio ? 



R. M. Laws: We are unable to study unexploited populations. Our 

 data do show, however, that at lower levels of exploitation some parameters 

 are different. These data — which are not very extensive — do not suggest 

 any increase in the percentage of unfertilized mature females following 

 exploitation, but rather the reverse. 



J. B. Cragg: Might not this situation arise in elephant seals, owing to 

 the heavy and selective exploitation of bulls ? 



R. M. Laws : It can certainly happen above a certain level of exploita- 

 tion. But it has not yet done so in fm whales, where the population units 

 are small and keep together as groups. In polygynous species, like the sperm 

 whale, rising exploitation may well affect the reproductive rate of mature 

 females. 



A. Jonsgard: In monogamous species the critical condition will be 

 whether a male and female are able to meet. 



T. B. Reynoldson: The increasing efficiency of catching will probably 

 affect the population in many ways. Does hunting seem to be causing 

 genetic and behavioural changes ? 



R. M. Laws : Asdic certainly induces changed behaviour, and marking 

 returns suggest that exploitation as a whole has modified the pattern of 

 dispersal of whales. However the data are not really adequate. Generally 

 speaking, whales migrate over a fairly constant path and return each year to 

 the same part of the Antarctic. One marked animal has however been found 

 to move through i8o degrees of longitude, and others through quite large 

 arcs. 



J. G. Skellam : It will be difficult to relate the catch size to fishing effort 

 owing to the continually varying methods of hunting. However, new 

 methods must overlap with old ones in time. Has any attempt been made 

 to cahbrate one method or one type of equipment in terms of another 

 which it is supplanting ? 



R. M. Laws : The possibility of doing this has been looked into, but 



