Spatially congruent sites of importance for global shark and ray biodiversity

Discussion We describe four major findings. First, there was low overall spatial congruency when compar- ing the hotspots of all three measures of species richness (total species, ED species, and endemic species), offering a small area of focus for future conservation planning exercises. Even though those areas of spatial congruency are small in extent, they comprise approxi- mately two thirds (64%) of all shark and ray species. Second, when comparing congruency pairwise between different species richness measures, ED species richness had the highest per- cent of overlap with total species richness, irrespective of spatial resolution or hotspot defini- tion. These two findings were consistent for all shark and ray species, as well as for the subset of threatened species only. Third, congruency across the three richness measures for all threat- ened species is relatively insensitive to hotspot definitions (from 2.5% to 10% of richest cells) and was consistently low across these definitions. Fourth, increasing cell size (from 1˚ to 8˚) lead to a two-fold increase in congruency between all species richness measures generally. These results have implications for shark and ray biodiversity, our knowledge of the different dimensions of biodiversity and how they can differ through space, and the effect of resolution in understanding spatial congruency. In contrast to Ku¨per et al. [46], who demonstrated that there was a higher congruence of plant biodiversity when hotspot was redefined, we found that the extent of spatial congruency

identified was low overall for the three measures of richness (total species, ED, endemic spe- cies) for all shark and ray species and the threatened species only. These results highlight con- siderable differences in the spatial distribution patterns of some biodiversity hotspots for sharks and rays, depending on the species richness measure used. The low congruency we have found between different measures of richness caution that it might be inappropriate to use total species richness as the sole feature of biodiversity to focus conservation attention towards. Our findings highlight that hotspots identified with other desirable species richness measures can be lost if there is a sole focus on total species richness, which has been a common strategy in identifying important areas for conservation [10,47]. If congruency among these hotspots identified with the different richness measures were high, then it would be reasonable to assume that relying on any one measure would be adequate to determine important areas for conservation that represented all three richness measures. However, our results demon- strate that this is not the case, and that not considering certain species richness measures can result in the exclusion of important features of biodiversity for conservation attention (e.g. endemic, threatened, evolutionarily distinct species). The low level of spatial congruency between the species richness measures also means that a relatively small fraction of the world’s ocean area could provide a tractable focal point for global shark and ray conservation. How-

ever, we caution that this kind of focal conservation strategy would still need to account for the opportunities and challenges presented by differing social, economic and cultural contexts [48,49], in addition to the abundance, dispersal abilities, and activity patterns of the wide range of shark and ray species [50]. Interestingly, there was a relatively high spatial overlap of 43% between the hotspots identi- fied for ED species richness and total species richness, when considering all shark and ray spe- cies. For the threatened species however, this overlap was considerably lower, at 4.02%. This Fig 4. (a) Spatial congruence between global hotspots (defined at richest 5% of all grid cells) of three species richness measures: total species (purple), evolutionarily distinct (ED) species (green), and endemic species (red). Spatial congruence between hotspots derived for all three measures are represented by orange cells. Map insets highlighting specific areas of overlap: (b) North and South America, (c) southern Namibia, South Africa, and southern Mozambique, (d) Japan, Taiwan, and parts of southern China, and (e) Australia. Areas of congruence between total species richness and ED species richness are in blue. Grid cell resolution is 1˚. The data used for this figure under CC BY license is granted permission from the International Union for the Conservation of Nature (IUCN), original copyright 2011. https://doi.org/10.1371/journal.pone.0235559.g004 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 9 / 19