The habitat of thirty species of sharks, rays, and chimaeras, also called ghost sharks, overlap with areas where proposed deep-sea mining may occur, according to new research published in Current Biology and led by University of Hawai'i at Mānoa oceanographers. Nearly two-thirds of these species are already threatened with extinction due to human impacts, so deep-sea mining, which will disrupt the seafloor and discharge large plumes of sediment into the water above, has the potential to elevate their extinction risk.
"Deep-sea mining is a new potential threat to this group of animals which are both vital in the ocean ecosystem and to human culture and identity," said Aaron Judah, lead author of the study and oceanography graduate student in the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). "By identifying and calling attention to this threat and recommending potential conservation pathways, I hope we will be better positioned to support healthy shark, ray, and chimaera populations into the future."
Where there is overlap, there is risk
Judah collaborated with an international team of experts to overlay the global maps of species ranges created by the IUCN Shark Specialist Group with contract areas and reserved areas allocated for deep-sea mining by the International Seabed Authority. The researchers also accounted for how each species reproduces and how deep they dive in order to estimate their vulnerability to mining impacts. For example, species such as skates and chimaeras lay eggs on the seafloor and therefore mining vehicles could pose a threat to nurseries.
The species they assessed included iconic examples such as the whale shark, manta rays, and the megamouth shark, and also many lesser known, but just as interesting deep-sea species, such as the pygmy shark, chocolate skate, and point-nosed chimaera, which comes from a unique group of cartilaginous fishes similar to sharks and rays, sometimes called ghost sharks.
The team discovered that 30 species could be impacted by discharge plumes and 25 of the 30 species could also be impacted by seafloor disruptions associated with mining. They also found that because many of the species inhabit a variety of habitats along the depth range or are deep divers, mining impacts may overlap more than half of the depth range of 17 species.
Assessing risk to minimize impacts
Deep-sea mining is set to potentially occur in the Clarion-Clipperton Zone, which is a large abyssal plain area that spans from the waters around Hawai'i into the eastern Pacific Ocean. To make the best management decisions, the potential impacts on marine life and the communities that depend on them must be known.
"Sharks and their relatives are the second most threatened vertebrate group on the planet, mostly from overfishing," said Jeff Drazen, study senior author and professor of Oceanography at SOEST. "Because of their vulnerability, they should be considered in ongoing discussions of the environmental risks from deep-sea mining, and those responsible for monitoring their health should be aware that mining could pose an additional risk."
The authors offer a number of recommendations to improve conservation of these species under the footprint of mining, such as establishing monitoring programs, including them in environmental impact assessments, and creating protected areas. These recommendations could be adopted by the International Seabed Authority in their regulations for creating environmental impact assessments, or by contractors in executing scientific baseline assessments.
"Many of the shark species identified in the analysis are highly mobile and can move across wide swaths of ocean," said Judah. "Given their mobility and the proximity of Hawai'i to the areas allocated for mining, impacts in these areas may stretch indirectly to ecosystems near the island chain."
Judah continues to research and report species range extensions for animals not included in the initial assessment, which may add additional species to this group of animals at risk from mining impacts.
