Sharkie Hotspots

An area being described as having high "biodiversity" means there are a large number of species living within that particular region or habitat. Sometimes we refer to biodiversity in general terms; including all different species of plants and animals, and sometimes we refer to more specific groups; such as assessing the biodiversity of insects in different habitats or the biodiversity of tree species in different forests. We also talk about "endemic species", which refers to a species of plant or animal which only lives in one region and is not found anywhere else in the world.

Blacktip reef sharks (Image Credit: Frank Baensch, Source:www.frankbaensch.com)

Assessing biodiversity is important because it can be critical for conservation initiatives, for protecting endangered species. Scientists can take 2 different strategies to conservation: 1. protecting individual species which have been assessed to be vulnerable to extinction or 2. protecting areas with high biodiversity, which are critical habitats for many different species. The latter, involves zoning off important regions, so they cannot be disturbed by human activity or exploited for their resources (by fisheries, mineral mines etc.) Conservationists aim to prioritise the protection of areas with especially high biodiversity or with endemic species living there. Some areas are designated as Marine Protected Areas (MPA), meaning they are protected from exploitation for conservation purposes.

Map of global Marine Protected Areas (MPAs) (Source: www.mpatlas.org)

"Condrichthyans" (sharks, skates and rays) are one of the most threatened groups of vertebrates globally. We currently know of more than 1,100 different species of chondrichthyan fishes, of which around 450 are classified as sharks and 600 are classified as "batoids" (skates and rays). As much as 1/4 of all these species are considered threatened (either as 'vulnerable', 'endangered' or 'critically endangered') on the International Union for the Conservation of Nature’s Red List of Threatened Species (IUCN). This is because they are overexploited in fisheries and their habitats are degraded by human activity. They are also especially vulnerable to extinction because they are very slow growing, late to become sexually mature, have long life-spans and have relatively low numbers of offspring throughout their lives. This means they struggle to recover if the population experiences severe declines.

Sharks and rays in an aquarium (Image source: www.posterlounge.co.uk)

Therefore, a recent study sought to use all available scientific literature describing the range of each chondrichthyan species, in order to map their individual distributions and highlight areas where there was cross-over between species. These areas would be described as having high shark and ray biodiversity or high "species richness" (this is a measure of biodiversity). The researchers used several different measures to assess species richness, including: total chondrichthyan species richness, threatened total species richness, endemic chondrichthyan species richness and threatened endemic species richness. When considering all of these measures together, they concluded that chondrichthyan biodiversity hotspots can be found in:

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,

7. eastern and western Australia.

Areas of high shark and ray biodiversity (Derrick et al, 2020)

The researchers discovered that when considering all sharks and rays, highest species richness was found along equatorial coastlines and no hotspots were found in the pelagic ecosystem (aka the open ocean, away from land masses). They noted that there were also several regions outside of the biodiverse tropics, at higher latitudes like South Africa, Australia and the east coast of South America. Threatened sharks and ray species, were also found in these regions.

They concluded that this pattern probably occurred because the high "productivity" (meaning the rate of production or the fertility of a given habitat) of tropical coastlines generates complex habitats and which can support the evolution of many different species.

Areas with high levels of endemic shark and ray species (Derrick et al, 2020)

However, they found that endemic species richness followed a slightly different pattern. All endemic species were found on coastlines (rater than in open ocean habitats) and the species richness when considering only endemic species, was highest outside of equatorial regions. The researchers noted that these hotspots occurred at the boundaries of tropical; and temperate ecosystems. This was especially true in the southern hemisphere, where there were endemic species hotpots in Australia, South America and South Africa. These areas were also where the highest richness of endangered endemic species could be found.

Colclough’s shark (Source: www.knowledgebase.lookseek.com)

Endemic species are especially vulnerable to extinction because their restricted geographical range, limits their ability to relocate if their habitat is damaged or destroyed. For example, the Colclough’s shark (Brachaelurus colcloughi) can only be found within 2° of latitude on the Australian east coast, in rocky reef habitats (Kyne et al, 2011). They are currently categorised as 'vulnerable' by the IUCN and their population size is decreasing. Protection of this species' habitat specifically as an MPA would be very beneficial for their conservation.

Currently, MPAs encompass some of the biodiverse regions in the Gulf of California, South Africa, eastern and western Australia and the Galapagos in Ecuador. There are also sites proposed for MPA in south-east Asia. However, there are many regions identified in this study which are not protected as marine protected areas. Whatsmore, regarding threatened endemic species, MPAs do not yet seem to be sufficient to ensure protection for them all. We must continue to work to implement more legislation to protect areas of critical biodiversity and increase the size of our MPAs globally.

You can learn more about Marine Protected Areas at the Atlas of Marine Protection. You can also support the process of implementing new MPAs by supporting your local conservation groups in the UK, Europe, USA, South Africa.

References

Derrick DH, Cheok J & Dulvy NK (2020). Spatially congruent sites of importance for global shark and ray biodiversity. PLoS One, 15:7, e0235559. Access online.

IUCN (2020) International Union for the Conservation of Nature Red List of Threatened Species. Access online.

Kyne PM, Compagno LJV, Stead J, Jackson MV & Bennett MB. (2011). Distribution, habitat and biology of a rare and threatened eastern Australian endemic shark: Colclough’s shark, Brachaelurus colcloughi Ogilby,1908. Marine and Freshwater Research, 62, 540–547. Access online.

By Sophie A. Maycock for SharkSpeak.