Therefore, with the new size limit, it would 

 still be possible to have a smaller total poundage 

 in a given year than previous years. 



Influence of Other Parameters 

 on Yield 



We have already demonstrated the importance 

 of different natural mortality estimates on 

 yield. Therefore, we should explore the possible 

 influence of some other estimated parameters 

 used in the yield equation: specifically, F, k, 

 t , and t„ or p . 



In the cubic expansion, we considered the 

 influence of instantaneous fishing mortality 

 by 0.5 increments. In the binomial expansion, 

 we had to use one estimate of F in each run. 

 Therefore, we changed F from 2.2036 to 1.0000 

 with the same other parameters in two of the 

 runs. As might be expected, the increasing 

 trend of yield in weight per recruit is relatively 

 unaffected by the F values (trend lines [C] and 

 [F] binomial, Fig. 18). 



A change in the k estimate from the von 

 Bertalanffy Growth Equation influences the 

 yield estimates in the cubic expansion. For 

 example, if k is halved (actually reducing the 

 carapace length for time t), then the yield in 

 weight per recruit is reduced with the same 

 other parameters (trend lines [C] and [D] 

 cubic, Table 11). Although this reduction does 

 change the magnitude of the yield, it does not 

 alter the general increasing or decreasing trend 

 of this line. 



Because of the relationship of k to t , we 

 might expect the hypothetical age at zero 

 length t to influence the magnitude of the 

 yield estimates without affecting the general 

 trend, at least within the different values that 

 we considered. Indeed, this is the situation 

 ( [D] and [E] cubic, Table 11). 



If t p and p are changed from 1.0 to 3.0 to 

 4.0 in the binomial expansion with a natural 

 mortality of 0.2664, we note a decreasing trend 

 in yield in weight per recruit in each case ([A] 

 with [D] and [E] binomial. Table 11). Con- 

 versely, with the lower natural mortality, we 

 note that with t p or p = 1, the trend line 

 increases in either case ( [B] with [C] binomial, 

 Table 11). I reasoned that only in the un- 

 realistic situation of t p or p = 1 with the also 

 unlikely high natural mortality, would there 



be a discrepancy in the increase or decrease 

 of the trend in the yield estimates. 



I concluded from this series of changes in 

 the described parameters that even if the origi- 

 nal estimates were not exact, we would reach 

 the same management recommendations as we 

 would with the precise parameters. Of course, 

 it is most advisable to use the verified values 

 in the yield equation because we can then better 

 predict what would happen with certain popu- 

 lation conditions and corresponding manage- 

 ment proposals. 



Discussion 



As stated earlier, I have not advocated a 

 reduction in effort to achieve maximum sus- 

 tainable yield (or maximum net economic gain), 

 rather, a change in the minimum size limit 

 to improve the yield under other existing con- 

 ditions. 



In my view, economists and some population 

 dynamicists have overlooked one very impor- 

 tant point, at least for the United States, in 

 the field of fisheries control. That is, few if any 

 State or Federal agencies in fisheries have re- 

 ceived the confidence of the fishing fraternity 

 (commercial or sport) or legislators to entrust 

 regulations entirely to that agency. 



In order to gain recognition from these people, 

 we must proceed in a step-like fashion: namely, 

 biological minimum size limits, where needed. 

 The recognition of improvement in a fishery 

 through a change in the regulation on size 

 or age at entry would then make it possible 

 to demonstrate the benefit of effective effort 

 controls that are biologically and economically 

 oriented. 



CONCLUSIONS AND 

 RECOMMENDATIONS 



Based upon this study, I recommend raising 

 the minimum legal size to 89-mm (3-V2 inches) 

 carapace length, and elimination of the 127-mm 

 (5 inch) maximum size regulation. The survey 

 of the commercial fishery should continue in 

 order to determine if there would be any changes 

 in the estimated parameters that we used in 

 the yield equation. Indeed, if there were 

 changes in the critical parameters, then we 

 should adjust the minimum size accordingly. 



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