sustainable yield" of the living resources primarily 

 as food for human consumption. 



To give food usage a preferred status is unsound 

 economically. For example, only a tiny fraction of 

 the product of the Peruvian achovetta fishery is 

 consumed directly. But the fishery provides inex- 

 pensive, high grade fish meal, oil and other 

 by-products which have been of great value to the 

 Peruvian economy as a whole. Apart from this 

 restriction, which is contained in no other fishery 

 convention, the objective sought by the conven- 

 tions is a biological result which has been concisely 

 summarized by Professor Crutchfield as follows: 



The key variables determining production possibil- 

 ities from a fish population can be grouped under 

 four headings: rate of entry into the "fishable" age 

 (recruitment); growth rates of individual fish; 

 natural mortality (from disease, old age, and 

 nonhuman predators); and fishing mortality. In 

 the absence of human intervention, any marine 

 population tends toward a maximum aggregate 

 weight, or biomass, at which net increments to 

 stock from recruitment and growth are exactly 

 offset by decrements from natural mortality. 

 Thus, at zero and at maximum population the 

 instantaneous rate of change in the weight of the 

 fishery population is zero. At intermediate levels, 

 the aggregate weight of the stock, in the absence 

 of other disturbances, will tend to rise toward its 

 maximum value, and the instantaneous rate of 

 change in weight will be positive. 

 Assuming for the moment that recruitment and 

 growth rates are independent of population size, 

 these relationships can be translated into a simple 

 physical production function. As fishing effort 

 (expressed in terms of standard units) is increased 

 from zero level, sustainable yield- that is, the 

 catch equal to the instantaneous rate of change in 

 the biomass in the absence of fishing by man- 

 increases at a decreasing rate while the number and 

 average size of fish will decline continuously. If 

 the selectivity of the gear with respect to fish of 

 different sizes is held constant, the sustainable 

 yield will peak at some level of fishing effort 

 Further increases in fishing effort will produce an 

 absolute decline in sustained physical yield. The 

 common sense of this is apparent Assuming a 

 recruitment rate independent of population and a 

 sigmoid growth function, fishing by man would 

 yield a larger net physical product as long as the 



marginal reduction in weight losses from natural 

 mortality is greater than the marginal rate loss 

 resulting from capture of individual fish before 

 they achieve maximum weight.^ 



The biological concept of maximum sustainable 

 physical yield has been criticized essentially on the 

 ground that "the management of fisheries is 

 intended for the benefit of man not fish, there- 

 fore, the effect of management upon fish stocks 

 cannot be regarded as beneficial per se."" Indeed, 

 unless the end products of the fishery are worth 

 more in money than the cost of producing them, 

 why have a fishery at all? Physical yield becomes 

 important only if the value of the fish is assumed. 

 For example, if part of the capital and labor now 

 emplo>ed in the salmon fishery were diverted to 

 catching flounders and dogfish, the physical out- 

 put, in weight, of fish, could probably be ex- 

 panded considerably. Obviously, it would make no 

 sense to do this— but only because it would reduce 

 the value of the catch to consumers and producers. 

 It is also impossible to adhere strictly to a 

 biological concept in any case in which two or 

 more ecologically interdependent species are being 

 exploited. Of necessity, the conservation objective 

 must then be stated in terms of a maximum 

 sustainable composite yield producing the greatest 

 market value. 



In every case, however, economists would 

 implement the conservation objective of fishery 

 management with the objective of maximizing the 

 net economic return (total revenues minus total 



Crutchfield, The Marine Fisheries; A Problem in 

 International Cooperation, 54 Amer. Econ. Rev. 207, 

 209-10 (1964). Crutchfield recognizes that: 



the assumption that recruitment is independent of popu- 

 lation obviously cannot be of completely general validity. 

 For anadromous fish such as salmon the relationship is 

 critical. Nature is so prolific in her production of 

 fertilized eggs, however, that the case in which the 

 number of fish surviving to catchable size is independent 

 of the total biomass over relevant ranges is the rule rather 

 than the exception. The other assumptions are less 

 tenable. Growth rates are almost certain to be density 

 dependent as are some types of natural mortality and the 

 production possibilities implicit in the foregoing analysis 

 are not necessarily reversible. As the size of the desired 

 stock is reduced through commercial fishing, permanent 

 shifts in predator-prey relations and in relative numbers of 

 competing food users may occur. Moreover, large and 

 frequent shifts in parameters are inevitable in the ecologi- 

 cal setting of the sea. Id. at 210. 



''Burkenroad, Some Principles of Marine Fishery 

 Biology, Publications of the Institute of Marine Fishery 

 Biology, Vol. 2, No. 1, University of Texas, 1951. 



VIII-46 



