FISHERY BULLETIN: VOL 76, NO. 2. 



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A B 



Figure 2.— A. Typical phase-plane graph of net productivity B = P - Y, Equation (6). the Graham system, with mortality F 

 constrained to the interval <F <4rnlB-j:. When removal rate 7 exceeds latent productivity P then S < and the negative branch of 

 Equation (6) applies. When productivity P exceeds removal rate Y then fi > and the positive branch applies. B. Typical solution 

 graphs of stock biomass B( t) , Equation ( 7 ) . When Y >P, biomass declines from initial value B^ towards adjustment level S* . When Y < 

 P, biomass increases from initial value S^ towards adjustment level B^. 



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A B 



Figures.— A. Typical graph of net productivity B =P -Y, Equation(6), the Graham system, with mortality F ^AmlBy,. Foranysuch 

 value of F, the zero root of Equation (6) applies, removal rate Y exceeds latent productivity P, and B <0. B. Typical solution trajectory 

 B(t) of Equation (7) when F & Am!B^. Biomass declines from initial value B,, towards extinction level B = 0. 



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