the estimates of total mortality were accurate. On the other hand, a 

 relatively small error in oomputud total mortality might cause errors 

 great enough seriously to affect the final interpretation of the results. 

 Thus it will be desirable, in the more precise determinations to be made 

 in the future, to place special emphasis on accuracy in computing total 

 mortality. 



sui^caRY 



1. If it is assumed for a given population that fishing effort is 

 uniformly distributed, and that instantaneous coB^ctition between units 

 of gear is absent, it is possible to estimate natural mortality, fishing 

 mortality, and rate of recruitment. 



2. The source data required are: (1) Age composition of the com- 

 mercial stock, (2) total catch per season, and (3) relative amount of 

 effort expended per season. Each of these must be known for at least 

 two periods during which the fishery was relatively stabilized. 



3. Total mortality may be estimated directly from the age composi- 

 tion of the stock at any time after stabilization. 



U. Natural mortality may be separated from fishing mortality by 

 assuming various ratios between the fishing mortalities for the tviro periods, 

 and making successive trials until a combination giving the knovm ratios 

 between the amounts of effort for the two periods is found. 



5. Rate of recruitment may be estimated by extrapolating the natural 

 and fishing mortality rates from the first fully available age class 



to the entering age class, 



6. Errors in the source data \/ill affect the estimate of natural 

 mortality the most seriously, and the estimate of fishing mortality during 

 the second period the least seriously. 



LITERATURE CITED 



Baranov, F. I. 



1918. On the question of the biological basis of fisheries. Nauchnyi 

 issledovatelskii iktiologisheskii institut, Izvostia I (1), 

 pp. 81-128, 12 figs, 



Clark, Frances N. 



1936. Interseasonal and intraseasonal changes in size of the California 

 sardine ( Sardinops caerulea ). California Div. of Fish and 

 Game, Bui. No. U7, 215 pp. U tables, 10 figs, 



1939. Measures of abundance of the sardine ( Sardinops caerulea ) 

 in California voters. California' Div. Fish and Game, Bui. 

 No, 53, h$ pp., 19 figs., 7 tables. 



179 



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