Effect of marine reserve establishment on non-cooperative fisheries management

Resource management in fisheries under different types of externalities in a two-country general equilibrium model of international trade

Open access resource problems and harmful pollutants from manufacturing activities are common in resource management practices. Nevertheless, their implications have only been studied in different and separate frameworks that are not covered within the same structure. Previous studies suggest that resource management enforced by one country can increase welfare levels and rebuild resource conservation, compared to the case where no country imposes resource management policies. However, in real-life examples, the harvesting and manufacturing industries exert simultaneous pressure on fishery resource stocks, thereby changing the nature of the supply curve of renewable resources. This study investigates the effects of trade liberalization under unilateral resource management regimes in a two-country, two-sector model, in which both production sectors can detrimentally affect renewable natural resources by generating two interacting environmental burdens: excessive harvesting and industrial pollution. It is demonstrated that unilateral resource management applied by a country in which the resource-good sector is relatively less damaging to fishery stocks is welfare-reducing for both countries compared to the situation where neither manages its resource sector. This result is identified as "immiserizing resource management." Notably, however, unilateral resource management by one country in which the resource-good sector has a more significant negative impact than the manufacturing industry can benefit both trading partners in welfare terms; this is referred to as "improving resource management." Policymakers in international organizations should consider the relative dominance of externalities in the presence of weak property rights before requiring resource management as a condition for participating in international trade.

Spillover-mediated harvesting competition: Effects of fishing ground configuration on fisheries targeting transboundary species

Overfishing is the main threat to sustainable fisheries and the loss of marine biodiversity. The race-to-fish phenomenon is a central driver of overfishing, and it prevails from small-scale to large-scale management regardless of whether spatial-right-based fisheries management has been implemented to ensure the ownership of fishery resources. In practice, the fishing grounds of resource users create complex configurations. Systematic understanding of harvesting competition across these configurations is necessary to promote sustainable fisheries management. Here, we developed a spatially-explicit model to analyze various scenarios of harvesting competition between two user groups using a game-theoretic approach. We found that realized harvesting competition was largely determined by the configuration of fishing grounds and an ecological mechanism where the ecological rescue effect could escalate harvesting competition, leading to a low population size. Our results also suggested that the implementation of voluntary no-take marine protected areas could largely mitigate harvesting competition. This suggests that the coordination of user groups is essential to resolve the race-to-fish.

Long-Term Conservation Effects of Protected Areas in Stochastic Population Dynamics

Terrestrial and marine protected areas are essential tools in mitigating anthropogenic impacts and promoting population persistence and resource sustainability. Adequately implemented protected areas (PAs) aim to promote conservation by increasing population size and reducing its variability. To resolve how these effects depend on PA features, I develop and analyze new models of stochastic processes that encompass the fluctuations generated by demographic or environmental stochasticity in PAs management. The stochastic model is built upon individual processes. In the model, density-independent mortality, migration between PAs and non-PAs, organism preference for PAs, and size characterize the features of the PA. The effect of PAs size is also examined. The long-term conservation effects are quantified using the coefficient of variation (CV) of population size in PAs, where a lower CV indicates higher robustness in stochastic variations. The results from this study demonstrate that sufficiently reduced density-independent mortality in PAs and high site preference for PAs and immigration rate into PAs are likely to decrease the CV. However, different types of stochasticity induce rather different consequences: under demographic stochasticity, the CV is always reduced because PAs increase the population size therein, but an increased population size by PAs does not always decrease the CV under environmental stochasticity. The deterministic dynamics of the model are investigated, facilitating effective management decisions.

On the spillover effect and optimal size of marine reserves for sustainable fishing yields

Marine reserves are an essential component of modern fishery management. Marine reserves, which represent a management tradeoff between harvesting and conservation, are fundamental to maintenance of fisheries. Finding optimal reserve sizes that improve fishing yields is not only of theoretical interest, but also of practical importance to facilitate decision making. Also, since the migratory behavior of some species influences the spillover effect of a marine reserve, this is a key consideration when assessing performance of marine reserves. The relationship between optimal reserve size and migration rate/mode has not been well studied, but it is fundamental to management success. Here, I investigate optimal reserve size and its management outcome with different levels of spillover via a simple two-patch mathematical model. In this model, one patch is open to fishing, and the other is closed. The two-patch model is aggregated by single-population dynamics when the migration rate is sufficiently larger than the growth rate of a target species. At this limit, I show that an optimal reserve size exists when pre-reserve fishing occurs at fishing mortality larger than f_MSY, the fishing mortality at the maximum sustainable yield (MSY). Also, the fishing yield at an optimal reserve size becomes as large as MSY at the limit. Numerical simulations at various migration rates between the two patches suggest that the maximum harvest under management with a marine reserve is achieved at this limit. This contrasts with the conservation benefit which is maximized at an intermediate migration rate. Numerical simulations show that the above-mentioned condition for an optimal reserve size to exist derived from the aggregated model is necessary when the migration rate is not sufficiently large, and that a moderate migration rate is further necessary for an optimal reserve size to exist. However, high fishing mortality reduces this requirement.