Management of a renewable natural resource such as stock of fish is key to sustainability of the resource. While simulating the population of a renewable resource such as fish stock, we expect the system (Stock & harvest) to converge to a steady state equilibrium (i.e. initial stock is in the basin of attraction). However, this is often not the case since there is a likelihood of experiencing a complex dynamic behavior including deterministic chaos where steady state equilibrium is never reached. Consequently, managing a fishery becomes a nightmare. What are some of the key determinants of such complex dynamic behaviors & how should a resource economist deal with such problems as far as managing a renewable natural resource is concerned?
Socio-economic and cultural characteristics of the fisher folks, sustainability indicators, climate change and policy environment.
One key determinant of the equilibrium state is a reliable stock-recruit relationship; simply put, when the population of adults is high, the number of fish born that live to be big enough to catch is also high. But this relationship is not often well-understood despite being the basis for most management. And this is but one source of variability.
Fisheries are typically managed in our region by assessing the population size with stock modeling and/or fishery independent indices in relation to thresholds established through historical stock performance or biological limitations. When thresholds are exceeded or approached, the only tactic we use is to reduce fishing effort, including reallocation among user groups. Fortunately, we have an adequate command and control regime so that reductions in effort lead to population growth, although not always does the response happen quickly enough. And we are still vulnerable to the mysteries of recruitment variability!
In my opinion first we need understand what the different fish ontogenetic phases need to complete the life cycles. If you want to manage the adult fish stock you have to give a chance to the species complete their cycle. Nursery areas must be identify and must be protected. This is the key point for the management around the world. All the best!
Mario
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