314 



Fishery Bulletin 89(2). 1991 



bias. In light of this, the general utility of the Wetherall 

 method clearly depends upon whether fish populations 

 actually reach equilibrium, or conditions close enough 

 to equilibrium, so that the consequent bias will be small. 

 We believe, however, that equilibrium conditions may 

 prevail more frequently than generally perceived. For 

 example, ehu Etelis carbunculus, another deepwater 

 snapper caught by Hawaii's bottomfish fishery, dis- 

 plays considerably less variability in size between years 

 than opakapaka. Chi-square tests, performed on annual 

 length-frequency samples of 3000 fish collected in 

 1984-88 (Fig. 5), are always not significant for ehu 

 (1986, P = 0.19; 1987, P = 0.40; 1988, P = 0.11) but are 

 always highly significant for opakapaka (1986-88, 

 P< 0.001). Therefore, the ehu population is apparent- 

 ly close enough to equilibrium that using the Wetherall 

 method would be appropriate. In general, however, the 

 Wetherall method should be used with extreme cau- 

 tion on new or changing fisheries or species experien- 

 cing recruitment fluctuations. In all cases, its use 

 should be preceded by a statistical verification of 

 population equilibrium. 



Citations 



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1971 Practical nonparametric statistics. John Wiley, NY, 

 462 p. 

 Csirske, J., J.F. Caddy, and S. Garcia 



1987 Methods of size-frequency analysis and their incorpora- 

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1987 Mortality rates of snappers and groupers. In Polovina, 

 J. J., and S. Ralston (eds.), Tropical snappers and groupers: 

 Biology and fisheries management, p. 375-404. Westview 

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 1989 Effect of seasonal recruitment on bias of the Beverton- 

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