Environmental offsets, resilience and cost-effective conservation.

Conservation management agencies are faced with acute trade-offs when dealing with disturbance from human activities. We show how agencies can respond to permanent ecosystem disruption by managing for Pimm resilience within a conservation budget using a model calibrated to a metapopulation of a coral reef fish species at Ningaloo Reef, Western Australia. The application is of general interest because it provides a method to manage species susceptible to negative environmental disturbances by optimizing between the number and quality of migration connections in a spatially distributed metapopulation. Given ecological equivalency between the number and quality of migration connections in terms of time to recover from disturbance, our approach allows conservation managers to promote ecological function, under budgetary constraints, by offsetting permanent damage to one ecological function with investment in another.

Complementarity of no-take marine reserves and individual transferable catch quotas for managing the line fishery of the great barrier reef.

Changes in the management of the fin fish fishery of the Great Barrier Reef motivated us to investigate the combined effects on economic returns and fish biomass of no-take areas and regulated total allowable catch allocated in the form of individual transferable quotas (such quotas apportion the total allowable catch as fishing rights and permits the buying and selling of these rights among fishers). We built a spatially explicit biological and economic model of the fishery to analyze the trade-offs between maintaining given levels of fish biomass and the net financial returns from fishing under different management regimes. Results of the scenarios we modeled suggested that a decrease in total allowable catch at high levels of harvest either increased net returns or lowered them only slightly, but increased biomass by up to 10% for a wide range of reserve sizes and an increase in the reserve area from none to 16% did not greatly change net returns at any catch level. Thus, catch shares and no-take reserves can be complementary and when these methods are used jointly they promote lower total allowable catches when harvest is relatively high and encourage larger no-take areas when they are small.

Economics of overexploitation revisited.

About 25% of the world's fisheries are depleted such that their current biomass is lower than the level that would maximize the sustained yield (MSY). By using methods not previously applied in the fisheries conservation context, we show in four disparate fisheries (including the long-lived and slow-growing orange roughy) that the dynamic maximum economic yield (MEY), the biomass that produces the largest discounted economic profits from fishing, exceeds MSY. Thus, although it is theoretically possible that maximizing discounted economic profits may cause stock depletions, our results show there is a win-win: In many fisheries at reasonable discount rates and at current prices and costs, larger fish stocks increase economic profits. An MEY target that exceeds MSY and transfers from higher, future profits to compensate fishers for the transition costs of stock rebuilding would help overcome a key cause of fisheries overexploitation, industry opposition to lower harvests.