Determining the appropriate spatial scale of management in fishery planning

Nao Takashina
(Kyushu University)

2014/11/18, 13:30- at Room 3631 (6th floor of building 3 of the Faculty of Sciences)

      The success of any spatially explicit management (e.g., establishing no-take zones) will rely on the spatial scale of management. For any managed region, managers must decide how much to subdivide the area under concern: from implementing a uniform approach across the region to a unique approach in each of hundreds patches and everything in between. However, there is no general theory for how the spatial scale affects management outcomes such as optimal fishery profit and biomass. To explore this question, I construct a mathematical model that follows an age-structured-harvested population in a one-dimensional patchy environment connected by larval dispersal. The spatial scale of management determines the number of managed segments in the region, within which fisheries take place or managers introduce a reserve so as to maximize the aggregate fishery profit. Assuming no cost to subdividing the region (e.g., implementation cost), I find that the aggregate fishery profit increases with the number of segments. Specifically, if the habitat landscape is positively autocorrelated, then the aggregate fishery profit increases with diminishing returns. This fact suggests that if cost to subdividing the region increases with the number of segments and the habitat distribution is positively autocorrelated, an intermediate management scale is likely to maximize net fishery benefit.
     This work was done in collaboration with Marissa L. Baskett (University of California, Davis).

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