Spatially congruent sites of importance for global shark and ray biodiversity

biodiversity measures. Extent of spatial overlap between hotspots was calculated using the fol- lowing equation [22]: Total proportion of overlap ¼ P Cn P An Where C is equal to the areas of congruence for each species richness measure, A the total distributional area of species richness measure hotspots, and n the number of species richness measures used to calculate congruence. To explore our original choice of hotspot (5%) or choice of spatial resolution (1˚), we also calculated spatial overlap for two different definitions of hotspot (richest 2.5% and 10% of cells), and two levels of coarser spatial resolution (4˚ and 8˚ grid cells). All analyses were carried out using ArcGIS Pro 2.4.3 [43] and R v.3.6.1 [44,45]. Results In general, the distributional patterns of total and ED species richness spanned the global ocean environment while endemic species were confined to the coastlines (Fig 1; S1 and S2 Figs). We focus our presentation of results and discussion of overall biodiversity patterns and congruency on the 5% definition criterion over all three resolutions (1˚, 4˚, and 8˚). The results did not greatly differ between the three definitions of species richness hotspot (Fig 2; S3–S11 Figs; S1 Table). Biodiversity hotspots for all shark and ray species were greatest near the equa- torial coastlines for all measures except endemic species richness (Fig 3). There are clear devia- tions from the well-known latitude-richness relationship, with no species richness hotspots present around equatorial coastlines (i.e. East Africa, Central Brazil, and Central America) and

some richness hotspots occurring in high latitude locations, particularly in the southern hemi- sphere (notably South Africa, Atlantic South America, and Australia; Fig 3A). These biodiver- sity patterns are more apparent for the subset of threatened species only (Fig 3D–3F). The distribution of ED species is broadly similar to the total richness pattern, but with a notable deficit along the northern coast of South America, particularly the Northwest Atlantic and eastern Pacific coastlines (Fig 3A and 3B). The anti-tropical distribution of endemicity hot- spots is most strongly present in the southern hemisphere (Fig 3C and 3F). In general, there was very low spatial congruence when comparing the hotspots of all three species richness measures (total species, ED species, endemic species; S1 Table). Cumulatively, all three biodiversity hotspots (for 1˚ resolution at 5% richest cells) occupied an area of 32,162,358 km2, of which only 5.78% (1,859,971 km2) were spatially congruent between all three hotspots (orange cells; Fig 4A). These eight areas of congruency occurred off the coasts of: (1) Northern Mexico Gulf of California, (2) USA Gulf of Mexico, (3) Ecuador, (4) Uruguay and southern Brazil, (5) South Africa, southern Mozambique, and southern Namibia, (6) Japan, Taiwan, and parts of southern China, and (7) eastern and western Australia (Fig 4B– 4E), and in total contain over half (64%) of all marine sharks and rays. The hotspots calculated for the subset of threatened species followed a similar pattern, albeit with considerably lower

spatial congruency. The hotspots derived from all biodiversity measures (at 1˚ resolution) for threatened species only covered a cumulative area of 28,839,224 km2 with a mere 1.51% (436,506 km2) of overlap between the three biodiversity hotspots (Fig 5A). The 1.51% of over- lap occurred off the coasts of: (1) Brazil and Uruguay (making up nearly two thirds of the total area; 286,767 km2), (2) South Africa, (3) Taiwan, and (4) eastern Australia (Fig 5B–5E). In total, these areas of overlap comprise 37% of all marine shark and ray species. Of all pairwise comparisons of spatial overlap, congruency between total number of species and ED species of all shark and ray species was consistently the highest (average of ~43%), and this remained true across all definitions of hotspot, as well as levels of spatial resolution (Fig 2; PLOS ONE Spatially congruent sites of importance for global shark and ray biodiversity PLOS ONE | https://doi.org/10.1371/journal.pone.0235559 July 6, 2020 4 / 19