Local fisheries have rapidly expanded to global trade markets with almost 40\% of seafood internationally traded. The threat to the sustainability of the species worldwide creates the pressing need for actions and institutions to manage the interplay of different markets. We have developed a bio-economic fishery model to assess different market structures, global, local and multi-level markets, in its effect on serial exploitation and the stability of income and fish populations. Using this simple model, we find evidence that market structure influences the equilibrium strategy of the fisher harvesting two species. Species collapse and subsequent serial exploitation occurs in all market structures. We find slight asymmetries in prices between the species stabilizing, strong asymmetries lead to overexploitation of the high value species. Policies that aim to decrease income fluctuations and increase fishers income might best come together at high effort levels for r-strategist species, and low to intermediate effort for K-strategist species, thus taking into account mainly biological factors. We show that the profitability of fishing at low effort or low population levels is beneficial in a local market. This may encourage fast entry into an exploratory fishery and fishing until collapse in a small and shrinking population without changes in income per unit effort. Another effect, we consider equally important, is the limitation of incentives in local markets to overharvest a large population because of reduced income per unit effort. Thus, we hypothesize that enforcement of rules for the recovery of a species will soon pay off because of the self-limitation of the fishery in this market structure. In comparison, global market structures, with unlimited incentives to harvest, will need longer term commitments of organization, rules and enforcement to secure sustainable incomes and species populations. Perfect price discrimination in multi-level markets combines the worst of both worlds, providing no incentive to stop harvesting at both low and high population levels.

Methods: Dynamic Systems Modeling/Bio-economic Modeling

People: Laura Elsler, Maja Schlüter

Funding: MuSES, Mistra, GRAID