Port location for inshore fleets affects the sustainability of coastal source–sink resources: Implications for spatial management of metapopulations

This paper focuses on the consequences of a geographical differentiation in reproductive potential through a species range not being recognized in the management of a coastal fishery resource. A dynamic spatial model with age-structure and bioeconomic components was built to explore the potential effects of fishing port location on metapopulations with a source–sink structure. Management of this type of fishery using marine protected areas (MPA) with or without considering the location of source and sink components is also addressed. An array of unit areas for a multi-age semi-sedentary resource was fed with recruits generated by a Beverton–Holt spawner–recruit relationship driven by the adult biomass in a source area. This contributes recruits both to source areas, and adjacent sink areas which do not produce recruits. Recruits are allocated to unit areas in the array according to a negative binomial distribution, allowing age structures to build up in each. Exploitation is from one of two ports, either situated close to the source area or distant from it; it being assumed (as for inshore fleets) that distance traveled is a key variable. Effort exerted per unit area is therefore determined by dynamic site-specific profits. Because fishing costs increase with distance, the alternative port locations are predicted to have substantially different impacts on biological and economic performance variables when there are no spatial management measures in place. Closing half the source area to fishing mitigates substantially the effect of port location, and improves all performance variables regardless of port location. The greatest positive impacts of a closure occur where the main port harvesting the resource is the one nearest the source area being protected.

When a spatial closure is applied, the average distance harvesters travel from a port close to the source is predicted to increase for all levels of fishing intensity, while distances traveled by fishermen from a port near the sink areas are predicted to decrease. If an MPA is established outside the source area, it is predicted to result in deteriorating production and net revenues because fishing intensity will tend to increase in the unrestricted source area.