![]() Increased export of larvae and recruits and increased catch per unit effort (CPUE), and in some cases, total catches outside boundaries have been documented for MRs and fisheries closures in coral reefs, temperate rocky reefs, continental shelf and estuarine environments. However, recovery of depleted populations within reserve boundaries and larval and/or adult spillover into adjacent areas may increase catches within a few years to decades from reserve establishment, thereby generating both conservation and fisheries benefits. Thus, the establishment of MRs is often perceived as trading off fisheries yields and profits for conservation objectives. Establishment of MRs reduces the extent of fishable areas, thereby potentially causing immediate economic losses and hardship to fishers. Moreover, concerns about whether MRs can increase or even just maintain fisheries catches still remain. Empirical evidence of the conservation benefits of MRs has rapidly accumulated over the past years, but reviews have highlighted limitations of the design and interpretation of empirical assessments. However, outcomes of MR establishment have been highly variable, and an active debate has been going on for a couple of decades on what social and ecological impacts might be expected. The use of marine reserves (MRs)-areas where extractive activities are prohibited-is a spatial approach to marine conservation and management aimed at protecting depleted populations, conserving and restoring whole ecosystems, and replenishing fisheries through larval and adult spillover. Recent evidence of widespread decline of marine populations and extensive loss of marine ecosystem functions and services critical to human well-being has emphasized the need for more effective approaches to marine conservation and resource management. ![]() We also show that environmental variability may mask fishery benefits of reserve implementation and that MRs may buffer against collapse when sustainable catch quotas are exceeded owing to stock overestimation or systematic overfishing. Modelling results predict that the net fishery benefit of MRs is lost when gains in fecundity of old, large individuals are small, is highest in the case of sedentary adults with high larval dispersal, and decreases with adult mobility. By using a stage-structured, spatially explicit stochastic model, we show that catches under quota-based fisheries that include a network of MRs can exceed maximum sustainable yield (MSY) under conventional quota management if reserves provide protection to old, large spawners that disproportionally contribute to recruitment outside the reserves. Previous models show that reserve establishment in overcapitalized, quota-based fisheries can reduce both catch and population abundance, thereby negating fisheries and even conservation benefits. Clear expectations of the possible outcomes of MR establishment are needed to guide and strengthen empirical assessments. Despite major investments in MRs, their environmental and social benefits have proven difficult to demonstrate and are still debated. Thus, in cases such as ours, improvements in management performance from adopting statistically powerful experimental designs may not outweigh the potentially high cost of measuring the effects of enhancement on Pacific salmon.Marine reserves (MRs) are used worldwide as a means of conserving biodiversity and protecting depleted populations. In addition, economically optimal experimental designs for monitoring programs generally had low statistical power, partly as a result of the high cost of monitoring. The choice between monitoring and not monitoring depended critically on the probabilities placed on the alternative effects of enhancement. We used this example to identify the conditions under which monitoring can generate positive net economic returns and the characteristics of experimental designs for monitoring that yield the greatest net value. keta and must choose how much, if any, of that budget to allocate to monitoring. We applied this framework to a hypothetical problem in which managers have a fixed budget for constructing groundwater-fed side channels for chum salmon O. ![]() We developed a quantitative framework based on decision analysis to determine whether the expected value of the information obtained through monitoring exceeds the costs of obtaining it. However, the costs of such monitoring can be substantial. Monitoring the performance of pilot projects before deciding whether or not to apply a particular method of enhancement on a wide scale will result in better investment decisions. Fisheries management agencies are involved in many activities to enhance Pacific salmon Oncorhynchus spp.
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