FISHERY BULLETIN: VOL. 86, NO. 1 



Table 3. In at least one case maximum and mini- 

 mum estimates differ by as much as a factor of 7 

 (i.e., young vs. old whitefish in Shakespeare Is- 

 land Lake, Ricker 1947, Table 3). 



The range of reported estimates of M for species 

 (rather than single groups or stocks within a spe- 



cies as compared above) is even greater. Even the 

 least variable estimates differed by a factor of 

 1.75 (75%, male vs. female plaice, Beverton 1964). 

 In whitefish, the species for which the most esti- 

 mates exist, maximum estimates are 20 times 

 greater than minimum estimates (Table 3). 



Table 3. — Ranges in estimates of instantaneous rate of natural mortality in unexploited and exploited fisfi populations. 'Wr^ax'''^min is 

 expressed as ffie ratio between tfie maximum (Mmax) and minimum (/Wmm) values reported for M for that species, Values in parenttieses 

 are total range of estimates and ratios for those species where multiple reports exist. 



'Increasing with age. 



2Year to year variation (1946-52); ages 15-23 combined. 



3Not consistent with age. 



"Generally increasing with age. 



SAssuming 20% tag loss rate, 

 spor tag loss rates from 10 to 30%. 

 78 different years (1967-75). 

 823 different year classes (1947-75). 



38 



