Modeling the impacts of area closures on the Hawaii longline fishery: A spatial-temporal economic model incorporating fish movement

Area closures have been widely used in the management of migratory fish and conservation of endangered marine species, but very few economic models are available to assess the impacts of a closure because economists have paid little attention to complexities in fishery management, such as spatial heterogeneity in fish stocks and fleet dynamics. This study presents a spatial economic model that features (i) heterogeneously distributed stocks of multiple species, (ii) their movement across areas, (iii) travel costs depending on fishing location, and (iv) optimal allocation of fishing trips to areas and of the primary target in each fishing set. Because catch-per-unit-effort (CPUE) diminishes with effort, trips are alternately allocated to several areas, where the expected crew's wages are equalized. While this optimal allocation of trips derives a demand for labor (DDL), fishermen's tradeoff between offshore days (labor) and onshore days (leisure) yields an upward-sloping labor supply curve, which determines, together with the DDL, the equilibrium level of wage and labor.Using catch and effort data summarized from the federally mandated commercial logbooks into 5° square monthly strata, auction price data, and survey data for longliner's cost structure, this model is applied to the Hawaii longline fishery to conduct policy simulations. While a near-shore area closure leads to fewer trips of longer duration, a closure of the North Pacific to protect sea turtles significantly reduces swordfish catch and significantly increases the catch of near-shore species, which may endanger the stocks of near-shore species or affect the harvests by other boats. The impacts of prohibiting swordfish sets on the industry could be more severe than the above closure for turtle conservation. A revenue tax is not effective in reducing fishing effort.A closure increases fish movement (FM) from the closed area to open, neighboring areas, resulting in higher levels of the stocks in those open areas. This FM effect benefits the fishery industry, and could reduce the fishermen's income loss from a closure--estimated by the model without FM--by half, if fish are mobile and the closed area(s) is a "source" in terms of the direction of movement.