Measuring the effectiveness of a Caribbean oceanic island no-take zone with an asymmetrical BACI approach

No-take zones (NTZ) provide an effective tool for biodiversity conservation and fisheries management. Increases in abundance and biomass within NTZs, with spillover effects to adjacent areas, have been documented. However, most studies occurred at highly connected sites near regions that can replenish the NTZ. In this study we assess NTZ effects within the Mona Island marine protected area (MPA), located within the Mona Passage, a partial biogeographic barrier. We used the robust asymmetrical before-after-control-impact (BACI) design to evaluate changes in population size for fishery target species four years after designation. Data on fish abundance and size were collected within randomly placed belt transects and roving surveys. Permutational multivariate analysis of variance (PERMANOVA) and similarity percentages (SIMPER) were used to detect changes in the coral reef fish assemblage and structure. Responses in abundance and biomass were calculated at different levels of the assemblage grouped by body size or ontogenetic stage. Additionally, univariate models provided insight on the magnitude and direction of NTZ effects. Results indicate significant increases in locations both open and closed to fishing, predominantly in the abundance of small-sized species and early life stages suggesting a recruitment signal. Significant distinctive performance within two locations was observed, with one showing a higher contribution of medium and large-sized species over time. Mona Island's MPA is apparently achieving its goals of fish stock restoration despite its isolation, although more time, enforcement and monitoring are essential to confirm these trends.