356 



DISCOVERY REPORTS 



The division of the catch into age groups may now be examined. Following the 

 attainment of sexual maturity whales are considered to give birth normally at recurrent 

 intervals of two years. Each two-year period is occupied in gestation (eleven and a half 

 months) and lactation (six months) after which is a resting period when the activity of 

 the reproductive organs subsides until the onset of the next sexual season. Each age 

 group should therefore consist of ovulating, pregnant, lactating and resting whales 

 covering the two-year period. It should be capable, moreover, of further analysis into 



OCT 

 IMMATURE — -O-- 



NOV DEC JAN 



SEXUALLY MATURE — 



FEB MAR APR 



PHYSICALLY MATURE 



Fig. i . Fin whales, females. Numbers of immature, sexually mature but not physically mature, 

 and physically mature whales in five complete seasons at South Georgia. 



a one-year grouping, the lactating and resting whales being a year older than those 

 ovulating or pregnant. At South Georgia, however, ovulating whales are rare and it has 

 been shown that breeding is, in all likelihood, restricted to northern waters. Ovulation 

 does occur exceptionally in the south but this does not necessarily involve copulation, 

 and may indeed be due to some pathological condition of the individual whale. Omitting 

 ovulation, then, the grouping of the South Georgia catch is limited to the pregnant and 

 lactating and resting whales, of which the full analysis for five seasons is shown in 

 Table II. 



