Natural Mortality 207 



several kinds of pan fishes of other investigators. There is some evidence 

 that annual mortality rates for longer-lived species are usually lower than 

 for bluegill and other pan fishes which arc relatively short-lived. 



Table 7.4 Annual mortality rates 



FISHES. 



FOR SOME COMMON HOOK-AND-LINE 



Fishing Mortality, Natural Mortality, and Recruitment 



Among warm-water fishes there is little evidence that a high mortality 

 rate either from natural mortality or fishing mortality or both, will seri- 

 ously reduce the angling potential of a fish population. This is because 

 the number of embryos produced during each spawning period is so 

 large, and the number that can find room to grow is so small, that a large 

 reserve is always available for a population to recoup its most severe 

 losses. Our information on warm-water fishes fails to demonstrate a rela- 

 tionship between the number of spawners and the number of embryos 

 surviving to reach the catchable stock. 



Many common warm-water species have short lives and high natural 

 mortality rates. Broods of such fishes as crappies and the sunfishes, the 

 white and yellow basses, and the several kinds of bullheads live but a 

 few years and are replaced. These fishes are subject to wide fluctuations in 

 abundance and in growth rates, and should be cropped when they are 

 available. With some exceptions, short-lived species are responsible for 

 many of the problems of fish management. 



