BIOLOGICAL BASIS 23 



able, and all species involve so many relationships for which accurate 

 measures have not yet been developed that designation ol any single 

 value as the maximmn sustained yield in natural populations ol 

 fish is impossible. Theoretical values can be calculated and are 

 essential in management programs, biu are hardly appropriate to 

 use as absoliue values— which have to be justified and proven for 

 any particular stock of fish. 



Nevertheless, the values of maximum sustained yield that have 

 been computed for such ^veil-documented fisheries as the north- 

 eastern Pacific halibut, are useful and are sufficiently accurate for 

 management. For example. Chapman, Myhre, and Southward (1962) 

 have developed refined estiinates of potential yield and stock size of 

 Pacific halibut. They demonstrate more clearly than has been done 

 before the temporal changes in productivity due to the fishery. Their 

 estimated maximimi yields are probably as accurate as can be derived 

 from a deterministic model ^vith existing data. Though they are 

 called only "first order answers" by Chapman (1963), their greatest 

 disadvantage is that they cannot be justified as true values incor- 

 porating all possible variables ^vhich affect the populations of fish 

 in natine. But they have played an essential role in providing 

 preliminary ans^vers for complicated ecological problems that so 

 far have been beyond the scope of theoretical developments. Chap- 

 man points out the advantages of stochastic models over determin- 

 istic ones, and indicates that further real progress in iniderstanding 

 the complex ecological systems involving fishermen, fish, and en- 

 vironment Avill probably come through simulation programs ^vith 

 large computers using Monte Carlo techniques Avith stochastic ele- 

 ments. Such work can have little relationship to reality without a 

 profound understanding of the qualitative as well as quantitative 

 relationships within these systems. With the extensive information 

 now available concerning the more important stocks and their 

 fisheries there is at present an excellent opportimity for carrying out 

 such computer studies. (See also Paidik and Gales, 1963.) 



Needless to say, the above paragraph does not mean to imply that 

 management of a high seas fishery should be dropped imtil final, 

 totally complete data are available. On the contrary, it suggests the 

 need for a continued program of progressive management, with a 

 view to constant improvement and refinement of techniques. 



