Abstract

Whenever assessing the effectiveness of marine reserves, it is important to have both outside reference areas (fished vs non-fished) and temporal comparisons for each (before vs after reserve declaration). This optimal situation is not commonly found, so inferences about effectiveness must be made from patterns of temporal variation alone. This is the case of Mona Island, a relatively isolated and unique no-take within the Mona and Monito Natural Reserve (MNR) located west of Puerto Rico. To infer effectiveness of the MNR, closed since 2010, temporal trends of the structure and composition of fish assemblages were assessed and compared to those of La Parguera Natural Reserve (LPNR), which is open to fishing. To achieve this, underwater visual censuses of fish (30 x 2 m belts of 10 min) were done at multiple sites (91 MNR to 140 LPNR), in different areas (3), during several times (5 MNR to 7 LPNR) between 2010 and 2018. Since assemblages in these two areas are known to be different, comparisons were based on temporal trends alone. It was hypothesized that: 1) effect sizes due to temporal variation would be greater than that of spatial variation, and 2) temporal variation in MNR would be greater than in LPNR. Multifactorial-multivariate linear models of total assemblage biomass showed that relative temporal components of variation (CVs) were greater in MNR (42%) than in LPNR (20%). Also, temporal CV in MNR was greater than any of the spatial CV, but this was not found for LPNR. Temporal trends in MNR were driven by 16 different species, 12 of which are commercially important. Out of those 12 species, 8 increased (snappers, groupers and parrotfishes) in biomass while the other four (all groupers) have decreased; indicating that MNR has been effective in protecting some of commercially important species in the region.

PDF Preview