Fig 1.
Location of northern U.S. Virgin Islands (St. Thomas and St. John) and St. Croix, separated by the Anegada passage.
Right panels show the insular shelf areas of the islands separated by fishery closure areas and areas open to fishing and divided into shoreline (<500 m from shore), shallow, and deep zones. Long-term fixed sampling sites of the USVI Territorial Coral Reef Monitoring Program and included in this study are indicated.
Table 1.
Submerged areas on the insular shelves of the northern USVI (N. USVI) and St. Croix with marine protected areas (MPA) and total fishable areas delineated by depth.
Fishable nearshore area was defined as the coastline to 500m offshore. This is included in the 0-25m shelf, but is highlighted separately as this zone is potentially vulnerable to shore-based artisanal fisheries. Digital Elevation Model and coastline data for the US Virgin Islands and surrounding areas were obtained from the NOAA National Geophysical Data Center (www.ngdc.noaa.gov).
Fig 2.
Relative fishing effort (determined by days fished) in the northern USVI and St. Croix [33].
Table 2.
Characteristics of 22 TCRMP fixed sites used for data analysis including the island grouping used in analyses, geographic location (decimal degrees), mean depth, categorical depth used in analyses (shallow = less than 25m, deep = greater than 25m), the years surveyed in the data set, living stony coral cover prior to mass mortality of the 2005 coral bleaching event, and mean rugosity.
Fig 3.
Relative encounters (% of transects in which the fish species was seen) for the fourteen target species at fixed sites of the USVI Territorial Coral Reef Monitoring Program.
Comparisons were made between island group and depth (<25 m and >25m). Asterisks (*) following species names indicate a significant overall model (α = 0.05). Carat symbol (^) for cubera snapper indicates that both depth and island were significant. Post-hoc analyses indicated as disparate letters over treatments where there was interaction between island and depth, and as a joining line where there was a significant across island effect. Nassau grouper was marginally non-significant for the overall model (p = 0.0567), but post-hoc analyses are presented for island and indicated with a dashed joining line.
Fig 4.
Total number of fish encountered in roving dives for eight of the large-bodied commercially important species in the northern USVI and St. Croix.
Data from fixed sites of the USVI Territorial Coral Reef Monitoring Program conducted between 2003–2011 (NN USVI = 174, NSt. Croix = 240).
Table 3.
Results of statistical analysis of relative encounters of fourteen large and medium-bodied commercially important species on belt transects at fixed sites of the USVI Territorial Coral Reef Monitoring Program.
Comparisons were two-way Friedmans Rank test comparing the treatments Island (St. Croix and the northern USVI), Depth (less than 25m and greater than 25 m), and their interaction (Island*Depth). All degrees of freedom were 3/18 (numerator/denominator) for the whole model and 2 for individual treatments. Where the model was not statistically significant the individual tests of treatments are not presented. Bold indicates significant treatments or interactions that were followed up with pair-wise tests.
Table 4.
Number of encounters of eight rare species in both roving dives and belt transects conducted by TCRMP from 2003–2011.
Encounters are reported by study area (Northern USVI and St. Croix) and strata. Years are collapsed. X indicates no encounters.
Fig 5.
Relative encounters for the fifteen target species in NOAA spatially-randomized transects conducted in shallow water less than 30 m depth (N = 10 for both the northern USVI and St. Croix).
* indicates a significant difference (p < 0.05) between Northern USVI and St. Croix relative encounters for that species as determined by a Wilcoxon test (statistical results in Table 5).
Table 5.
Results of statistical analysis of relative encounters of fourteen large and medium-bodied commercially important species in NOAA spatially-randomized transects conducted in shallow water less than 30 m depth (N = 10 for both the northern USVI and St. Croix).
Comparisons were Wilcoxon rank tests comparing island (St. Croix and the northern USVI). Bold indicates significant differences (p < 0.05).
Fig 6.
MDS ordinations of target species assemblages between northern USVI and St. Croix based on (A) fixed site data and (B) spatially-randomized data. Black triangles indicate northern USVI sites; Gray triangles indicate St. Croix sites. The 3D plots did not improve stress greatly (3D Stress = 0.11 and 0.06, respectively) and therefore are not presented.
Table 6.
Results of the SIMPER analysis between islands based on fixed (TCRMP) and spatially randomized (NOAA) datasets.
Fish species listed are the top five species that contributed the most to dissimilarity between the northern USVI and St. Croix multivariate data sets of species relative encounters.
Fig 7.
Total length (cm) frequency distributions for four common commercially important species based on fixed site (left column) and spatially-randomized (right column) surveys between the northern USVI (dark bars) and St. Croix (gray bars).
N indicated in graphs are number of fish.
Table 7.
Results of Kolmogorov-Smirnov tests using fixed site (TCRMP) and spatially-randomized (NOAA) data sets comparing size frequency distributions between the northern USVI and St. Croix.