PARENT SESSION
Oral Session 9: Marine Ecology I: Management.
Presiding: D Policansky
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room C 120.

Marine reserve spacing and fishery yield: When are practical designs optimal?

White, Crow^*,1, Kendall, Bruce¹, Siegel, David¹, Costello, Christopher¹, ¹ University of California - Santa Barbara, Santa Barbara, CA

ABSTRACT- Marine reserves have been proposed as a management tool that will both reverse declines in abundances of coastal species and generate "spill-over" that optimizes fishery yield beyond that attainable without reserves. Many studies have examined how these two goals are affected by the total fraction of marine habitat designated to reserve status, but few analyses have focused on the role of reserve spacing. Of those that address effects of spacing, all conclude that, for a given total reserve area, fishery yield can only be optimized through presence of either a single large reserve or an infinite number of infinitely small reserves - neither of which is practical. These results are based on reaction-diffusion models that cannot separate (in either space or time) the processes of larval production and post-settlement recruitment. Here, we analyze an integro-difference model that describes coastal marine species with sessile adults and dispersing larvae. This model decouples both the location and timing of larval production and recruitment, enabling us to allow post-settlement survival of larvae to depend on adult population density at each recruitment location. Such post-settlement density dependence is common in harvested marine fishes. Incorporating this life history trait into the model reveals that, for a fixed total reserve area, yield is optimized via a network of moderate-sized reserves that are spaced at intermediate distances along a coast. If reserve area is fragmented into too many small reserves, adult population density never gets very high anywhere; if reserve area is clumped into a only a few large reserves, populations inside increase, but few larvae disperse far enough to settle beyond the reserve boundary. Only through an intermediate sized reserve network is larval "spill-over" maximized, thereby optimizing harvest. The critical factor is that production of larvae is not limited in the reserve as the adult population density approaches its carrying capacity. In contrast, when larval production does depend on adult density, yield is optimized via a network of infinitely small reserves. These results have important policy implications for designing marine reserve networks that could enhance both marine species economic and conservation benefits, while also being feasible to manage.

Key words: spill-over, density dependent recruitment, marine reserves, reserve network design