- Scientists have described a new species of deepwater catshark based on four specimens caught in the bycatch of deep-sea shrimp trawlers, off Kerala’s coast.
- Researchers highlight the need to monitor its abundance, distribution, biology and mortality rates to determine its conservation status.
- The discovery highlights the rich diversity of deep-sea species in the region, much of which remains undocumented.
A deep-sea catshark caught off Kerala’s coast has now been identified as a new species, highlighting the need for better understanding of deep-sea biodiversity.
In 2022, a team of scientists sifting through the bycatch of deep-sea shrimp trawlers came across a black, slender-bodied fish with an angular, pointed snout and striking white eyes. This fish had been caught at a depth of 400-650 metres at Kollam slope, a continental slope in the southeastern Arabian Sea off Kerala’s coast, designated as an Important Shark and Ray Area. The team confirmed that it belonged to the genus Apristurus — a group of deepwater catsharks — and brought it back to the lab for further examination.
Two years later, the researchers collected three additional specimens at Sakthikulangara Fisheries Harbour, Kollam, during monitoring surveys. Through morphological and molecular analyses of the four specimens, the team found that this species was distinct from others within the genus and described it as a new species of deepwater catshark (Apristurus drona) in their paper published earlier this year in Zootaxa.
The objective of the study, part of a larger project under the Ministry of Earth Sciences’ Deep Ocean Mission, was to explore the diversity of deep-sea chondrichthyans which are cartilaginous fish such as sharks (Selachimorpha), rays and skates (Batoidea) and chimaeras (Holocephali) and resolve some of the taxonomic confusion around them.
“From biodiversity inventory surveys, we have realised that our understanding of deep-sea biodiversity is limited,” said Bineesh K.K., the study’s corresponding author and a scientist at the Marine Biology Regional Centre (MBRC), Zoological Survey of India (ZSI), Chennai.
Currently, the abundance, distribution and biology of this newly-described catshark remain unknown. “We can say this species is data-deficient,” said Bineesh, adding, “It is one of the ecologically important species, as sharks are apex predators. So, we need to know what its importance is in the deep-sea ecosystem.”
Taxonomically-confusing sharks
Apristurus, a genus of small catsharks in the family Pentanchidae, is considered one of the most species-rich genera of sharks. The 42 species currently recognised under this genus inhabit deep waters between 200 and 2,000 metres.
Although five species of this genus have been previously recorded in Indian waters, the status of all except one — Apristurus investigatoris recorded from the Andaman Sea — still has questions around it, explained Sweta Beura, the study’s lead author and senior research fellow at the MBRC, ZSI, Chennai. “So [A. drona] is the first species from India’s southwest coast in this genus,” she said. The study notes that “A. investigatoris is the only species with confirmed occurrence from the Indian coast.” The other four species — A. microps, A. canutus, A. indicus and A. saldanha — have questionable status in India, as their available records in India are scant.
Bineesh said that most of the Apristurus species are data-deficient and are known from only two-three specimens, noting that “the availability of samples for taxonomy are very less.” Beura added that these catsharks have subtle differentiating characters, “meaning taxonomically there is high ambiguity.”
This is where DNA barcode analysis is useful, said Ravi Ranjan Kumar, who earlier led a project searching for sharks in South Asian seas, supported by the Save Our Seas Foundation. He was not involved in the A. drona study.
To determine if A. drona was a distinct species, the team, comprising Beura, Bineesh and Dhriti Banerjee, extracted DNA from tissue samples collected while the specimens were still fresh. They then compared the species’ genetic sequence and physical characteristics with those of closely-related species within the same genus. A. drona differed genetically from its closest relative, A. nayakai from the southwestern Pacific Ocean, by 5.5-5.7%. “Normally, if a species shows 3% or more genetic difference, we can consider it as a new species,” Bineesh explained.
Of the three groups within this genus — brunneus, spongiceps and longicephalus — researchers classified A. drona under the Apristurus brunneus subgroup based on its characteristics.
“The description of Apristurus drona highlights the rich yet incompletely documented biodiversity in the deep-sea ecosystems of the region and how much remains to be discovered,” said Shoba Joe Kizhakudan, Principal Scientist and Head, Finfish Fisheries Division, Indian Council of Agricultural Research (ICAR)-Central Marine Fisheries Research Institute (CMFRI). She was not associated with this study, but added that three species including one shark (Filistriatus arabicus, Bascanichthys chepakakiensis, Cyttopsis indica and Apristurus drona), have been discovered in Indian waters just in 2026.
A shark rarely encountered in bycatch
Bineesh explained that between 2008 and 2022, there was a complete absence of this species in bycatch. “It is only in the last three-four years, when the fishermen increased their depth of fishing that this species has started to appear,” he said.
Deep-sea sharks are usually targeted for their meat and liver-oil. But these catsharks “don’t have any commercial value,” said Beura, adding that they are small with high water content. When caught incidentally by trawlers and longliners, they were earlier discarded but are now used as fish meal for poultry.
“A significant portion of sharks, because of their inherent life-history traits such as slow growth, low fecundity, and late maturation, combined with fishing pressure, are highly vulnerable to extinction,” said Kizhakudan. According to an International Union for Conservation of Nature (IUCN) report, over one-third of chondrichthyans are threatened with extinction due to overfishing.
Emphasising the need to maintain a balance in the deep-sea ecosystem, Bineesh explained that with rising global demand for deep-sea shrimp, especially the brightly-coloured red ring (Aristeus alcocki), fishermen who would earlier trawl at depths of 200-400 metres have increased their operations to 600 metres.
While fisheries are extending to previously-inaccessible depths, deep-sea fisheries remain limited in India and are monitored by ICAR-CMFRI, said Kizhakudan, adding that some bring bycatch of deep-sea sharks, but in low volumes.
Although fishing pressure may pose a threat to A. drona, which is currently known from Kollam slope and Wadge Bank areas, the extent of the threat is hard to determine without additional data. “If it is a micro-endemic species (restricted to a particular area), when you’re fishing in that area, it may become locally extinct or even completely extinct,” Bineesh said. “But we cannot say anything until we have more information.”
The need to monitor deep-sea species
Through systematic monitoring surveys, the authors hope to uncover answers about A. drona’s distribution, breeding, and mortality rates — both natural and due to trawling — and determine its conservation status. “If we know this species is rare, then we can propose conservation measures,” said Beura.
The study notes that deep-sea exploration and advances in molecular taxonomy could lead to more such discoveries and improve our understanding of deep-sea biodiversity. Since some species could be sustainably utilised for resources, future research should explore whether this species contains useful microbes or antimicrobial peptides that have potential application for humans, Bineesh noted.
Kizhakudan suggested setting up a research consortium of multiple institutes working in the deep-sea domain, adding, “While deep-sea shark research in India is evolving, we have yet to fully understand what is out there and how much it interacts with our fisheries. More funding and research should be diverted to deep-sea ecosystems and fisheries diversity.”
Banner image: Apristurus drona is the first new species of the genus to be described from India’s southwest coast. Image courtesy Bineesh K.K and Sweta Beura.
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