ABRAMSON and TOMLINSON; APPLICATION OF YIELD MODELS 



Table 6. — Monthly exploitation rates. 



June to September, was 0.16 for age II, 0.21 for 

 age III, and only 0.03 for age I. 



Biomass Estimation 



The Murphy method produces estimates of 

 population size in numbers at the beginning of 

 each catch interval. The present study also re- 

 quired estimates of biomass. Murphy (1966) 

 stated he computed biomass by dividing the 



catch in weight by the appropriate estimate of 

 E from his analysis of numbers in the catch. 

 This would result in a positively biased biomass 

 estimate, since it is equivalent to multiplying 

 the number alive at the beginning of a catch 

 interval by the average weight during the in- 

 terval. 



Two ways of computing the correct estimates 

 of biomass utilizing Murphy's method to esti- 

 mate numbers are possible; 



1033 



