FISHERY BULLETIN: VOL. 7K NO. 2, 1973 



different situations. Overall performance is 

 best with these hypothetical values for the 

 limit-mean model with offshore catch known, 

 and this model also provides estimates of fish- 

 ing and natural mortality rates offshore. 



9. Direct sampling for maturity in offshore 

 catches, when known by origin, would give 

 nominally unbiased estimators for all para- 

 meters but those mentioned last in Item 8 

 above, and further would i)ermit estimation 

 of survival or mortality during about the last 

 year at sea icitliont data on the number of 

 smolts. Although Atlantic salmon caught off 

 Greenland are nearly all immature (Horsted, 

 1971), it may be recommended for coho and 

 Chinook salmon caught off western North 

 America that a) maturity be monitored sys- 

 tematically by time and area and b) research 

 be intensified on determining catch by origin 

 indei)endently of marking smolts (e.g., separat- 

 ing hatchery fish from wild fish by scale 

 patterns). 



ACKNOWLEDGMENTS 



For their comments on earlier drafts of the 

 manuscri])t I thank J. A. Gulland of the Food 

 and Agriculture Organization of the United 

 Nations, D. G. Chapman of the University of 

 Washington, and K. A. Henry, G. Hirschhorn, 

 and D. D. Worlund of the National Marine 

 Fisheries Service. I am grateful to the editorial 

 referees whose suggestions led to the present 

 version. 



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524 



