16 FISHES AND FISHERY METHODS 



longed over-fishing, costs of production may exceed the value realized 

 from the catch. This usually prevents over-fishing of a population to the 

 point of extinction. 



Management 



Living resources of the sea are common property, open to all who 

 care to exploit them. They are important sources of food and recreation 

 for the entire country; it is, therefore, to the public's best interest that 

 they be managed to provide their maximum sustained productivity. 



Many marine species occur in extraterritorial waters and are exploited 

 by fishermen of several nations. Others are highly migratory, traveling 

 freely from waters of one nation to those of others. Management of such 

 species often requires conservation treaties among the nations concerned. 

 These treaties usually establish international commissions to effect the 

 rational use of the resources. 



Whether a fish resource is confined to estuarine waters or to the high 

 seas, the objective of management is the same, namely, to obtain the 

 maximum sustainable catch. There are several ways control agencies may 

 accomphsh this. The most direct way is through annual catch quotas or 

 restrictions on fishing intensity. Other management devices commonly 

 used include: minimum size limits which serve to protect the young, 

 fast-growing fish; closure of nursery areas to fishing; seasonal restrictions 

 to protect spawning populations which may be particularly vulnerable 

 to fishing during spawning activities; and restrictions on types of fishing 

 gear that may be used. 



Successful management of a marine resource requires detailed knowl- 

 edge concerning the life history of the species concerned. For example, 

 is the species resident or migratory? At what age and size does it first 

 reproduce? Is it particularly vulnerable to fishing during its reproduction 

 season? What is the relationship between the numbers of spawners and 

 the numbers of surviving offspring produced by them? What is the rate 

 of growth of different segments of the population? What fraction of the 

 population is dying from natural causes and what fraction is removed 

 by fishing? What is the size of the population? Answers to all these 

 fiuostions and more are required to successfully manage a resource. 



8ince World War II much progress has been made in developing 

 methods of obtaining answers to these questions. New analytical 

 approaches have evolved which greatly contribute to our understanding 

 of the complex mechanisms governing populations of marine organisms. 

 Investigators now have a number of methods available from which to 

 choose those best suited to the population they are studying. 



