Numbers of recruits, rather than recruitment or mortality 

 rate, must be plotted in order to determine the theoretical 

 level of maximum sustained yield (MSY) . If complete, linear 

 density-dependent recruitment rates applied, the maximum 

 number of recruits would occur at the peak of a parabolic 

 yield curve. The yield curve shown in Figure 5.20 was plotted 

 with the following assumptions: 1) the highest observed 

 recruitment rate occurred at the lowest observed density, 2) 

 the lowest observed recruitment rate occurred at the highest 

 observed density, and 3) the relationship was directly linear. 



600 



y- 500 



CO *- 



la 4o ° 



ll c 

 "SO. 300 



O T3 



-Q <D 



f= ~ 200 



18 



£ 100 



»-. 



N 



N 



V — r— 

 200 



400 600 800 1000 



Number of Adults - Spring (Nt) 



1200 



Figure 5.20. 



Yield in number of fawns recruited to 31 May 

 plotted against the number of adults in the 

 population on the previous 1 June. Dashed 

 curve represents theoretical yield curve 

 assuming complete linear density-dependent 

 survival . 



Yield in fawns recruited to 1 year of age plotted against 

 the number of adults in the population at birth pulse (Fig. 

 5.20) indicated that recruitment did not occur in a linear 

 density-dependent manner. If complete, linear 

 density-dependent recruitment occurred, all points plotted 

 should lie near the yield curve. As can be seen, yield was 

 much below "expected" levels at low densities and much greater 

 than "expected" at high densities. Within the observed range 

 of densities, maximum yield occurred at population levels 

 almost double those predicted by complete, linear 

 density-dependent recruitment. Although a maximal yield curve 

 for those data is drawn in Figure 5.20, it is apparent that 

 they do not closely follow any pattern. Yield was quite 

 variable at all observed density levels. There was also no 



154 



