According to Gurney and Nisbet (1998), ecosystem models using energy as their currency
might be unsuccessful because it is difficult to precisely define the energy outflows.
Therefore, modern ecosystem models often adopt one or more essential elements, usually
carbon, nitrogen, or phosphorus, as their currency (Gurney & Nisbet 1998). Numerous
ecosystem models have been applied to fisheries (e.g., Polovina 1984; Christensen et al.
2004; Fulton et al. 2004). Detailed descriptions and comparisons of these models can be
found in Plaganyi (2007), Fulton et al. (2004), and Fulton et al. (2003). From the economic
point of view, managers need to balance the economic value of fish in the present
and future with their ecological values. Therefore, ecological economic models for fisheries
need to integrate economic and ecological influences in order to assist managers in
determining appropriate levels of stocks and catches (Knowler 2002). The economic models
for EBFM may need to solve the problem of maximizing the net present value of fish
while constraining the interaction of physical and biological components of the ecosystem.
This is one way to take ecosystem structure and function into account and therefore to
include indirect use values of fish in the marine ecosystem.