Few regions on earth remain untouched by fishing activity. As such, effective longterm no-take marine reserves (NTMRs) and other area-based management systems that restrict fishing serve as vital reference areas for assessing the magnitude and recovery potential of marine ecosystems from human influence over both space and time. Much of the peer-reviewed literature and meta-analyses demonstrate variable but overall positive responses to such protection for fish and some other taxa. These include significant increase of stock species abundance and biomass within boundaries, cross-boundary spill-over of adults and larvae, and increased egg production. A reserve may meet its biodiversity objectives and contribute to fished stocks, however, determining the extent of that contribution depends on several factors. These factors include: understanding and monitoring the species biology, and the effectiveness of and compliance with management, and changes in fishing pressure external to the NTMR or other type of spatially-managed area from which some fishing activities are excluded. This presents significant data and cost challenges of scope, scale and monitoring method for assessment of NTMRs and fishery management throughout the, often extensive, range of the stock. The situation is one in which proof is hard to establish and absence of proof of effect is not proof of absence of effect (the issue of Type I and Type II errors in experimental design).