Global diversity hotspots and conservation priorities for sharks

Abstract

Sharks are one of the most threatened groups of marine animals, as high exploitation rates coupled with low resilience to fishing pressure have resulted in population declines worldwide. Designing conservation strategies for this group depends on basic knowledge of the geographic distribution and diversity of known species. So far, this information has been fragmented and incomplete. Here, we have synthesized the first global shark diversity pattern from a new database of published sources, including all 507 species described at present, and have identified hotspots of shark species richness, functional diversity and endemicity from these data. We have evaluated the congruence of these diversity measures and demonstrate their potential use in setting priority areas for shark conservation. Our results show that shark diversity across all species peaks on the continental shelves and at mid-latitudes (30-40 degrees N and S). Global hotspots of species richness, functional diversity and endemicity were found off Japan, Taiwan, the East and West coasts of Australia, Southeast Africa, Southeast Brazil and Southeast USA. Moreover, some areas with low to moderate species richness such as Southern Australia, Angola, North Chile and Western Continental Europe stood out as places of high functional diversity. Finally, species affected by shark finning showed different patterns of diversity, with peaks closer to the Equator and a more oceanic distribution overall. Our results show that the global pattern of shark diversity is uniquely different from land, and other well-studied marine taxa, and may provide guidance for spatial approaches to shark conservation. However, similar to terrestrial ecosystems, protected areas based on hotspots of diversity and endemism alone would provide insufficient means for safeguarding the diverse functional roles that sharks play in marine ecosystems.

Figure 1. Global pattern of total shark species richness.

The map indicates the number of shark species present in each cell of 1° longitude by 1° latitude. Richness hotspots of >50 shark species are coloured in bright green, yellow and red.

Figure 2. Relationship of shark species richness with (A) latitude and (B) longitude.

Negative numbers indicate latitude south or longitude west.

Figure 3. Shark conservation priorities.

(A) Richness pattern of 52 shark species affected by the shark fin trade. (B) Pattern of shark endemism, quantified as the sum of the inverse of the geographic range size of all species present in the cell. (C) Pattern of shark functional richness, quantified as the number of shark ecomorphotypes (as defined by Compagno 1990) present in the cell. (D) Priority areas for shark conservation; each area was selected because it contains either the top 5% of species richness or endemism for each of 93 major shark biogeographic units (areas characterized by the presence of a unique set of species as identified by a cluster analysis).