Source-sink population dynamics and the problem of siting marine reserves

Marine protected areas (MPAs) have been proposed as one way to reduce the p roblems of overfishing and to respond to uncertainty in fisheries managemen t, Many fisheries, including tropical and temperate reef fisheries, are inh erently multispecies, multigear fisheries and are difficult to manage by tr aditional methods. Clearly, these fisheries should benefit fi om the establ ishment of no-take marine reserves, but the track record to date for fisher ies benefits of MPAs is mixed or poorly documented. Because siting of reser ves depends upon both scientific and sociological input, the lack of critic al scientific information on source-sink population structure of reef fishe s can potentially lead to MPA placement that can damage rather than enhance fisheries. In this paper, we develop a simple, spatially explicit model to address a series of hypotheses regarding MPA effects on fisheries. Our hyp otheses include: (1) a system in which reserves are placed in source habita ts is superior to one in which they are placed at random or in sink habitat s; (2) the importance of source sink population structure is increased if f ishing effort is displaced rather than reduced; (3) as the proportion of th e environment consisting of poor-quality (sink) habitat increases, proper s iting of MPAs becomes increasingly important; and (4) if the environment co ntains directional currents, the spatial location of reserves will be criti cal to population enhancement. Our results suggest that, if reef fishes hav e source-sink population dynamics, siting reserves on the basis of sociolog ical criteria alone may be risky. We need to understand source-sink populat ion dynamics to site MPAs properly.