more or less self-contained and is self -renewing , that the 

 population level of an unexploited stock is at carrying 

 capacity, i.e., at the greatest level which environmental 

 conditions will support continuously, and that there are 

 no significant changes in carrying capacity during the period 

 of exploitation. The concept of MSY also assumes that the 

 rates of reproduction, growth and/or natural mortality of 

 a stock are density dependent, i.e., that the rates vary as 

 the population size or density in a particular area varies. 

 MSY further assumes that the kind of density dependence that 

 these rates exhibit is not such as to cause large amplitude 

 fluctuations in stock size and that the process of reducing 

 the initial stock by exploitation is a reversible one (Holt 

 and Talbot, 1978) . 



The MSY concept rests on the assumption that environ- 

 mental conditions are constant, and does not consider the 

 interactions between the target species and other species in 

 the same ecosystem which are related to or dependent on it 

 through predation, competition or other types of interactions. 

 In particular, the assumptions underlying MSY are strained 

 when more than one stock is fished in a given area (Gulland, 

 1978) . The MSY concept does not deal with the time scales 

 of changes in population size and population interactions. 

 Such time scales become particularly important when exploita- 

 tion at more than one trophic level is taking place (May, e_t 

 al. , 1979) . 



Even with MSY management as a goal, various fish stocks 

 have been overexploited unintentionally. Such overexploita- 

 tion has been attributed at times to inadequate data and 

 consequent incorrect estimation of MSY. At other times the 

 economic pressures brought to bear by an overcapitalized 

 fishing industry unwilling or unable to restrict catches 

 to MSY levels , or to reduce catch rates in order to allow 

 stock rebuilding, may have contributed to overexploitation . 

 In any case, single species management with MSY as an objective 

 has frequently failed as a continuous management strategy, and 

 has resulted in overexploitation and reduced rather than high 

 sustained yields. 



As understanding of ecological processes increases, it 

 has become apparent that there are significant factors af- 

 fecting renewable resource population dynamics which are not 

 taken into account in the theory underlying MSY and single 

 species oriented resource management. 



