FISHERY BULLETIN: VOL. 76, NO. 2. 



5 



\ n>i 



I 



I 



Thmshxyldipooje. 



5 



5(t; 



to 



Ym 



&, 



-/- 



an— I 

 o 



rt—t 



< F < 



"67 



implies V >P, £>o^&:ic 



implLes Y<Pr &o<&*. 



A B 



FiGL'RE 7. — A. Typical phase-plane graph of Equation (15) when n>\ and F<ymlB^, in which case root B^ >0. Should Y>P, the 

 negative branch of Equation ( 15) applies; should Y<P, the positive branch applies. B. Typical solution trajectories, Equation (16), 

 when n>\ and F<ym/B.x. Should Y>P, biomass trajectory B(t) declines from initial value Bq toward adjustment level B*. Should 

 ,Y<P, B(t) increases from B^ toward B*. 



\ (Zanqcof p 



I n >i 



I 1 



/ 



b(t) 





Ex-iinction 



A B 



Figures.— A. Phase-plane graph of net productivity Equation (15) when « > 1 andF ^ymlBy-. Forany such combination of n andF, 

 S* < and the zero root of Equation ( 15) applies. B. Typical solution trajectory. Equation ( 16), when « > 1 and F > ymlB^, in which 

 case the stock declines from initial value B„ towards extinction. 



386 



