Commercially exploited fish species are part of complex interaction webs, though most of the studies leading to fishery management only focus on small ecosystems. However, applying ecological network model to bioeconomic research is valuable in the advancement of the science of ecological economics because it incorporates more realistic dynamics of the marine ecosystem and human harvesting activities such as multiple harvesting that is common in the fisheries economy. Moreover, although ecosystem services are usually difficult to quantify and communicate, they are measured in a much easier way using economic effort and revenue, evaluated in terms of profits and employment. To study the declining productivity of fisheries and understand how human exploitation impacts ecosystem function, we modeled complex marine food webs using consumer-resource body-size ratios and non-linearities in feeding behavior. This model includes the greater number of species and harvested species, and unlike smaller models, it also contains properties of the network as variables. These newly added variables can directly affect the outcomes of model simulations. We started with the study of trophic networks with economic exploitation of multiple exploited species that model natural ecosystems more realistically. The population dynamics within the food webs were simulated using the same Allometric- Trophic-Network model.
Results/Conclusions
With complex food webs, the behavior of the system in the managed fishery scenario is simpler most of the time than what could have been expected. Apart from a few exceptions, the harvested species biomass monotonically decreases when the exploitation rate increases, whereas the small food chain model shows multiple regimes with complex relationship between biomass and harvest effort. The response of the system to an increased exploitation rate depends more heavily on the local properties of the web such as the harvested species metabolic rate and its prey vulnerability than on the global structure of the web.
Within a multispecies fishery, the selection of the species to harvest also determines the final equilibrium, profit, and employment. Thus, with proper management of the fishery, it is possible to optimize employment, yield, profit, or biomasses or to minimize the risks of extinction. Often, fisheries may optimize several or even all of these criteria.On the other hand, an inadequate understanding of the system is so crucial that it may lead to extinction of the harvested species or more endangered species and may result in irreversible consequences by a tiny change in the economic strategy of the firm.