Annual biomass budgets have been estimated for producer 

 and consumer components of ecosystems of the Ross Sea, the 

 Southern Ocean, and the California Current (Green, 1977, 

 1978) . These models contain compartments representing every 

 component of the marine ecosystems; frequently, many com- 

 ponents are lumped into one compartment for simplicity. The 

 models consider the nature of material flows between com- 

 partments and some of the factors regulating flow rates. 

 These models have the advantage of accounting for material 

 flow and production in an entire ecosystem, and the limita- 

 tion of highly simplified assumptions about the factors 

 controlling consumption rates. 



A more realistic treatment of consumption rates, at 

 least for fish stocks, in the North Pacific FCZis incorpora- 

 ted in the DYNUMES models (Laevastu and Favorite, 1978). The 

 DYNUMES models concentrate on interacting fish population 

 dynamics , do not consider plankton production dynamics , and 

 use forcing functions rather than population simulations 

 for marine mammals and other predators of fish. The DYNUMES 

 models are so complex that the underlying assumptions are 

 very difficult to discover and evaluate. 



These ecosystem modeling attempts demonstrate that some 

 degree of ecosystem level perspective, even for a complex 

 marine ecosystem, is possible with presently available data. 

 A review of existing ecosystem models with respect to their 

 potential applicability to ecosystem level fisheries manage- 

 ment would be a useful starting place for the incorporation 

 of ecosystem models into fishery management plans. 



Predator Prey Interactions 



More detailed models and theoretical treatment are avail- 

 able for predator prey relationships. For marine ecosystems, 

 simple models of harvesting at different trophic levels in a 

 multi-species foodweb have been considered recently (May, e_t 

 al. , 1979) . Quantitative treatment of predator prey inter- 

 actions as influenced by a fishery can and should be the 

 next step in developing an ecosystem perspective for fisheries 

 management. The example presented in Appendix F for estima- 

 ting the long term effects of the proposed northern anchovy 

 fishery OY on anchovy consumption by predators provides one 

 possible method for estimating fishery impact on food avail- 

 able to natural predators in an ecosystem. 



44 



