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Assessing the population-level conservation effects of marine protected areas |
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| Authors: | Daniel Ovando Jennifer E Caselle Christopher Costello Olivier Deschenes Steven D Gaines Ray Hilborn Owen Liu |
| Institution: | 1. School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA;2. Marine Science Institute, University of California, Santa Barbara, Santa Barbara, California, USA;3. Environmental Market Solutions Lab, University of California, Santa Barbara, Santa Barbara, California, USA
Bren School of Environmental Science and Management, University of California, Santa Barbara, Santa Barbara, California, USA;4. Environmental Market Solutions Lab, University of California, Santa Barbara, Santa Barbara, California, USA Department of Economics, University of California, Santa Barbara, Santa Barbara, California, USA;5. Bren School of Environmental Science and Management, University of California, Santa Barbara, Santa Barbara, California, USA |
| Abstract: | Marine protected areas (MPAs) cover 3–7% of the world's ocean, and international organizations call for 30% coverage by 2030. Although numerous studies show that MPAs produce conservation benefits inside their borders, many MPAs are also justified on the grounds that they confer conservation benefits to the connected populations that span beyond their borders. A network of MPAs covering roughly 20% of the Channel Islands National Marine Sanctuary was established in 2003, with a goal of providing regional conservation and fishery benefits. We used a spatially explicit bioeconomic simulation model and a Bayesian difference-in-difference regression to examine the conditions under which MPAs can provide population-level conservation benefits inside and outside their borders and to assess evidence of those benefits in the Channel Islands. As of 2017, we estimated that biomass densities of targeted fin-fish had a median value 81% higher (90% credible interval: 23–148) inside the Channel Island MPAs than outside. However, we found no clear effect of these MPAs on mean total biomass densities at the population level: estimated median effect was –7% (90% credible interval: –31 to 23) from 2015 to 2017. Our simulation model showed that effect sizes of MPAs of <30% were likely to be difficult to detect (even when they were present); smaller effect sizes (which are likely to be common) were even harder to detect. Clearly, communicating expectations and uncertainties around MPAs is critical to ensuring that MPAs are effective. We provide a novel assessment of the population-level effects of a large MPA network across many different species of targeted fin-fish, and our results offer guidance for communities charged with monitoring and adapting MPAs. |
| Keywords: | bioeconomic modeling causal inference Channel Islands National Marine Sanctuary marine conservation marine protected area networks program evaluation conservación marina inferencia causal modelo bioeconómico programa de evaluación redes de áreas marinas protegidas Santuario Marino Nacional de las Islas del Canal |