202 Fishing and Natural Mortality 



believed, but those inhabiting the cooler northern sections of the country 

 live longer than the same ones in the warmer southern and central 

 sections: Largemouth bass in northern Wisconsin may reach ages of 14 

 to 15 years; in central Illinois, 500 miles south, these fish seldom live 

 longer than 10 to 11 years. 



As a rule, the species that attain the largest sizes live the longest, al- 

 though in any single species, individuals that grow rapidly and gain 

 exceptional sizes are usually short lived for their species. For example, 

 when I was investigating the ages and growth rates of largemouth and 

 smallmouth bass in Wisconsin, I found that bass of 5 pounds or larger 

 were often not more than 5 to 7 years old. In contrast, the bass that showed 

 14 or 15 annuli on their scales (14+ to 15+ years) seldom exceeded 4 

 to 4.5 pounds in weight; none of the fishes of exceptional sizes for these 

 species were slow-growing individuals. It was as if a fish were "wound 

 up" like a mechanical toy when small, with the potential to run down 

 rapidly or slowly depending upon its individual genetic make-up, the 

 available food, and the forms of competition encountered. 



Table 7.1 gives approximate ages for some common fishes of interest 

 to anglers. Probably most of the ones that reach ages within the range 

 shown in Table 7.1 die of senility. 



Table 7.1 Approximate life spans of some sport fishes. 



Problems of Measuring Natural Mortality 



It is usually quite impossible to observe much more than casual 

 activities of the larger aquatic animals in the smallest and clearest ponds; 

 therefore, direct observation is presently of little importance for obtaining 



