Marine Protected Areas (MPAs) and No-Take Zones (NTZs) are increasingly championed as marine management solutions, by restricting activities like fishing. Assessing their effectiveness is important for evaluating whether conservation and/or sustainability goals are met. Baited Remote Underwater stereo-Video (stereo-BRUV) systems are one of many methods used to survey demersal fish and habitats, yet little is known about how spatial sampling designs can impact the detection of these management measures.
In this study, we first compared the detection of fish assemblage-level protection effects between two spatial sampling designs in two locations of southwestern Australia (Waatern Wagyl/Geographe Bay and Waatu Wagyl/Capes Region). We then simulated 36 scenarios (six spatial sampling designs, three modelled species distributions) across the same two locations 1000 times each, to understand the influence of spatial sampling design choice on the detection of changes in species abundance in NTZs.
In the empirical data collected, the two spatial sampling designs detected significantly different assemblages, although the effect of NTZs was consistent between the two designs. The performance of spatial sampling designs (mean bias, RMSE, interval coverage, effect size, and significance) in the simulations differed across species and locations, with stratified spatially balanced sampling most consistently representing the difference in abundance inside and outside the NTZs.
We recommend the use of stratified spatially balanced sampling designs in assessments of spatial management effectiveness, as they present advantages in performance at a local scale, as well as reusability of data across research questions.