248 R. J. H. BEVERTON 



notably by a reduction in the fecundity of females at a given age, but to test 

 the significance of these it is first necessary to examine the relation between 

 the size of the present population and the number of resulting progeny. 



COMPENSATION BETWEEN SUCCESSIVE ADULT 

 GENERATIONS IN PLAICE 



In plaice, twenty-six pairs of values of adult population weight and resulting 

 progeny are available, the number of the latter being estimated when first 

 recruited to the adult phase of the population at three to four years of age, 

 and these are plotted in Fig. 3 . 



75 100 125 



Index of adult populat-ion weight. 



Fig. 3. — Relation between biomass of adult plaice population and number 

 of progeny surviving to recruitment. 



The points to the left of the diagram refer to the low levels of adult 

 population size that occurred during the 1930's and again in recent years; 

 the points to the right resulted from the high densities during the war and up 

 to 1949, by which time the war-time accumulation had been largely fished 

 out. Yet over this tenfold range of adult population size there seems to be no 

 corresponding change in the numbers of recruits; even from the highest 

 adult densities the recruitment was only average. This can be shown more 

 strikingly by calculating the ratio of recruit numbers to adult population — 

 which can be regarded as an index of survival to recruitment — and plotting 

 it against adult population. The result is shown in Fig. 4, where the decrease 

 in this index of survival as adult population increases becomes evident; in 



