On the Utility of Bioeconomic Models for Fisheries Management 



GlULIO PONTECORVO^ 



ABSTRACT 



Short run and long run biological and economic models are inevitably bound to- 

 gether in any comprehensive plan to manage commercial fisheries. While these 

 disciplines can be treated rigorously, political and social considerations can be 

 considered only generally and therefore on an ad hoc basis. Within this framework 

 long run models are useful primarily for goal setting. More work must be done in 

 developing short run models which will measure the immediate biological and economic 

 impacts of alternative management steps in addition to immediate political and social 

 ramifications. Emphasis would then be placed upon the economic sources of short run 

 instability, with an initial economic rationalization of the fishery providing the funds 

 for subsequent management and biological forecasting which will concentrate on ex- 

 tending management from a rationalized fishery at a given harvesting level to rational- 

 ized fishing at some optimum level. 



BIOLOGICAL MODELS 

 The Yield from Ocean Resources 



A 19th century view was that the high seas 

 fisheries were inexhaustible. We who are pre- 

 occupied by our failure to control our own 

 numbers and the possibility of worldwide eco- 

 logical disaster can at best regard such notions 

 as quaint. Nevei-theless, certain implications 

 of the 19th century view of the oceans, with 

 its infinitely elastic aggregate supply curve 

 for fish, are worth considering here in our 

 attempt to understand the biologists' concept 

 of the maximum sustainable physical yield.^ 



The need for biological regulation of fish- 

 eries arose because the economic interests 

 involved in exploiting these resources became 

 aware, through rapidly declining yield-effort 

 relationships, that the supply of any particular 

 species was limited.' Recognition of the exis- 



' I wish to express my thanks for helpful sugges- 

 tions to Dr. Brian Rothschild and Dr. Edilberto Segura. 



- Professor of Economics, Graduate School of Busi- 

 ness, Columbia University. 



•' The elasticity of the supply function may be with 

 respect to the inexhaustibility of one stock of fish or 

 as indicated below it may arise from a process of sub- 

 stitution of one stock for another. 



■* The concept of limit is highly ambiguous. It may 

 be thought of as the maximum sustainable yield; the 



tence of these limits led the biologist to in- 

 vestigation of the characteristics of particular 

 populations in order to find, if possible, a 

 level of exploitation that would be safe. A safe 

 level is defined as that maximum rate of ex- 

 ploitation that would preserve the stock, and 

 yet allow the catch to continue at the maxi- 

 mum rate through time.'^ The imposition on 

 the stock of the appropriate (to achieve the 

 maximum sustainable yield) level of fishing 

 mortality involves the movement from one 

 long run equilibrium condition of the fish 

 population to another, with both equilibriums 

 considered stable. t* 



The development of the argument thus far 



level of scarcity of fish beyond which it would not 

 pay to fish, i.e., an economic limit, the level that maxi- 

 mizes the net economic yield from the resource, or in 

 complete destruction of the stock. 



5 For the development of an alternative view of 

 the relationship between the maximum sustainable 

 yield and the net economic yield, see (Schaefer, 1970a). 

 Schaefer also develops the necessai-y conditions for 

 adequate biological management (p. 9ff.) 



" The first equilibrium is the natural or unexploited 

 state of the stock. The second is the condition of the 

 stock being exploited at the maximum sustainable yield. 

 There is a question about the relative stability of 

 the two equilibriuijis both per se and also because 

 of the effect of fishing effort on ecological conditions. 

 More simply, populations that are heavily exploited 

 by fishermen may show gi-eater fluctuations in stock 

 size. 



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