FISHERY BULLETIN: VOL. 70. NO. 3 



Table 1. — Estimates of Schaefer model parameters, observed catch and effort, predicted population size and catch, 



population and catch in millions of pounds, effort in thousands of hours. 



hours, and an optimum population size (Popt) of 

 4.79 million pounds. Other parameter estimates, 

 as defined by Pella and Tomlinson, and the com- 

 plete output from the program are shown in 

 Table 1. 



Figure 1 shows both the expected catch as 

 predicted by the model and the observed catch 

 plotted against time. The fit appears to be gen- 

 erally quite good, although it has worsened dur- 

 ing the most recent 5 years. The statistic R, 

 derived by Pella and Tomlinson to measure the 

 improvement in estimating catch from this mod- 



el rather than from the mean catch, was 0.91. 

 However, a somewhat spurious R is obtained 

 when intervals with no catch are included in 

 the data. This occurs because the model always 

 predicts a zero catch from zero effort and the 

 arithmetic mean cannot make such a prediction. 

 Recalculating R from only periods when effort 

 was applied yielded 0.75. 



Figure 2 shows the fitted line (w = 2) for 

 catch per unit effort versus effort in the equi- 

 librium state and the observed catches per hour 

 by year. However, the population should not 



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