Commercially exploiting deep sea sharks for oil in Sri Lanka - a new threat on the horizon for sharks?

The bathymetry of Trincomalee Harbour in eastern Sri Lanka, containing submarine canyons, has enabled a seasonal artisanal bathydemersal elasmobranch fishery, supplying the international shark liver oil trade. The oil is... [ view full abstract ]

The bathymetry of Trincomalee Harbour in eastern Sri Lanka, containing submarine canyons, has enabled a seasonal artisanal bathydemersal elasmobranch fishery, supplying the international shark liver oil trade. The oil is utilised in shark liver oil tablets, poultry feed and aquaculture feed. Following extraction from livers via melting, the oil is transported to a production facility for purification where three oil quality grades of distinct density ranges are produced, each from livers of specific shark species. Preliminary morphometric data, identification photographs, sex ratio, maturity data, and tissue samples are being collected on the species landed in this fishery. Species sampled in Mutur (n=58) over 6 days include Centrophorus atromarginatus, Echinorhinus brucus and Neoharriotta pinnata, listed as Data Deficient on the IUCN Red List; Centroscymnus coelolepis and Hexanchus griseus, listed as Near Threatened on the IUCN Red List; sharks from the genera Iago, Mustelus and Planonasus; and skates from the genus Dipturus. Additionally, deep sea specimens sampled 100 kilometres south in Valaichchenai (n=51) over 87 days include Pseudocarcharias kamoharai, sharks from the genus Iago and skates from the genus Dipturus. Genetic samples are being sequenced to confirm species. The relatively short holding time of landed specimens will facilitate detailed studies of their feeding habits through stomach content analysis. Shark breeding grounds potentially exist on Sri Lanka’s east coast given observations of pregnant female sharks and from fishers’ anecdotal evidence. The data collected will facilitate the evaluation of their population status and help ascertain the sustainability of this fishery.