Volume 59

Spatial Variation in Fishing Intensity and its Effect on Yield

Ralston, S., O’Farrell, M.
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Date: November, 2006

Pages: 646

Event: Proceedings of the Fifty Nine Annual Gulf and Caribbean Fisheries Institute

City: Belize City

Country: Belize


Fishing mortality is rarely, if ever, evenly distributed over space, yet this is a common assumption of many fisheries models. To evaluate the effect of spatial heterogeneity in fishing mortality on yield, we constructed age-structured models that allowed for differing levels of fishing on three regions within the boundaries of a stock and made discrete assumptions about the life stage in which density-dependent compensation operates. Simulations demonstrated that spatial variability in fishing mortality could lead to yields exceeding the maximum sustainable yield (MSY) of the spatially uniform fishing case only when density-dependent compensation occurred in the post-settlement stage. However, spatially heterogeneous fishing could lead to greater yields than the spatially uniform case for all forms of density dependence when fishing mortality was very high (i.e., well above the fishing mortality rate that produced MSY). The yield premium generated in these simulations by the post-settlement density-dependence model appears to be due to the low levels of compensatory, density-dependent mortality in heavily fished areas coupled with dispersal of propagules into these areas from lightly fished adjacent regions

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