THE STOCK OF WHALES AT SOUTH GEORGIA 359 



Dividing each term by its predecessor the factor 1 — r is left, and thus between the 

 first six age classes (3-4 years to 13-14 years) the rate of reduction r has an average 

 value of 26 per cent, the actual figures being 27, 24, 26, 30 and 24 per cent. Beyond the 

 13-14 year class the rate of reduction is greater — 64, 60 and 75 per cent. For the first 

 six age classes the reduction is therefore regular, as if it were due to one source of loss, 

 but beyond 13-14 years the high reduction rates suggest that there is some other cause 

 which removes the older whales from the South Georgia population, or, perhaps more 



~i r 



20 21 



TWO-YEAR GROUPING O PREGNANT WHALES---* LACTATING OR RESTING WHALES - -C 



Fig. 2. Fin whales, females. Numbers of each age group in the total catch of five seasons: 



mature whales only. 



likely, that the old whales do not linger in these waters. They may even avoid the locality 

 altogether on their way farther south. 



Edser further calculates from these figures the number of immature females that must 

 become mature in order to keep the stock at a constant level, and also the number of 

 young females that can, in the most favourable circumstances, be produced by the 

 mature stock. 



By equating the sum of the first six terms of the algebraic series to the sum of the 

 first six catches 1 a has been calculated, and with a equal to 497 and r to 26 per cent the 

 theoretical catches based on the series and the stocks of whales in the corresponding 



/i - (1 - o- 2 6) 6 \ 

 o-20fl — — =415, i.e. the sum of the first six terms of the actual catch : from which a=4Q7. 



\i - (1 -0-26)/ * J +v/ 



