or on other aspects of the population dynamics of nontarget 

 species. There also was no consideration of the effect of 

 nontarget species on the population dynamics of the target 

 species, other than an estimated predation rate, assumed 

 to be constant, which was part of the MSY calculations. 



The treatment of marine mammals as nontarget species 

 in the plans was limited to the question of incidental take 

 and the minimization of entrapment of marine mammals in 

 fishing gear. There are both direct (ecological interactions) 

 impacts of marine mammals on fisheries and of fisheries on 

 marine mammals. Only the direct impacts were considered in 

 the plans. The impacts of marine mammals eating fish which 

 had already been trapped with some kind of fishing gear were 

 mentioned, but the impacts of a fishery on marine mammal pop- 

 ulation size and on food availability for marine mammals, as 

 well as the impacts of large marine mammal populations as 

 additional pressures on fishery populations undergoing in- 

 creasing harvesting, were not considered. 



IV. DISCUSSION AND CONCLUSIONS 

 CRITIQUE OF SINGLE SPECIES MANAGEMENT 



The conceptual and practical problems with single species, 

 MSY-oriented fishery resource management are considered in 

 this section of the report. Appendix G contains more detailed 

 discussion of the theory underlying MSY calculations, data re- 

 quirements, and the limitations inherent in the assumptions of 

 the MSY concept. 



Fisheries management has traditionally been concerned 

 with a single species, its population dynamics, and its maxi- 

 mum sustainable yield. MSY has been treated as an inherent 

 property of the population dynamics of a particular target 

 stock. The development of methods for calculating MSY has 

 focused on the target stock itself, the pattern of growth over 

 time of its individuals, the birth rate and the rate of sur- 

 vival to an age or size subject to being fished, and the rate 

 of fishing mortality and its relationship to fishing effort. 



The physical and biological environment of a target stock 

 have not been treated with a corresponding degree of detail. 

 Instead, environmental conditions have been assumed to remain 

 constant and the carrying capacity of the surrounding eco- 

 system for the target stock has been assumed to remain un- 

 changed throughout the duration of fishing on that stock. 



26 . 



