< 



LU 



Q 



-1.6 -1.2 -0.8 -0.4 0.0 



G -Z 



FIGURE 1. — Difference between arithmetic and exponential calculations of mean biomass 

 when dt = 1.0 and B t = 1.0, DELTA =B t iB, , exp - B ( , a nth ) = B t * ,0.0061 + 0.0037 <G, - Z, > - 

 0.1095 UG t - Z t > 2 1 - 0.0491 (<G, - Z,i 3 )j, r = 0.998. 



recruit. In one, B t was computed arithmetically, 

 and in the other it was computed exponentially 

 (Fig. 2). In both runs, the number of survivors was 

 followed across the intervals and biomass was 



5,000 



tracked within each interval. There were obvious 

 significant differences. Evaluating various 

 F-multiples and ages of entry, when B t was cal- 

 culated arithmetically, the maximum yield ex- 

 ceeded the maximum biomass of the stock ( 5,522.6 



4,000- 



3,000- 



1,000- 



\Q 



«n o m o mo mo 



<s m Mm dm N « 



~ f< -r « -: cm "■ f* 



«" ~ n  *• • in 



n 



m 



AGE AT ENTRY 



AGE AT ENTRY 



FIGURE 2. — Yield per recruit estimates for bluegills of Muskellunge Lake calculating mean biomass a) arithmetically and b) 



exponentially (data from Ricker 1975: table 10.3). 



447 



