First oarfish sighting in Sri Lanka highlights citizen science in marine protection

Scientists have documented the first-ever record of an oarfish (Regalecus russellii) in Sri Lanka, a 2.6-meter (8.5-foot) specimen caught off the country's western coast.

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The find expands the known distribution of oarfish into the Indian Ocean, offering a new baseline for studying this rarely seen deep-sea species. Meanwhile, another oarfish was recorded in India's Tamil Nadu this year, while within 20 days, three oarfish have been recorded from Australia and New Zealand, puzzling naturalists. The importance of promoting citizen science and raising awareness among fishers is needed.

In the shadowy depths of the ocean lives a ribbon-like giant crowned with a fiery red crest long mistaken for a sea monster. Rarely glimpsed alive, the oarfish holds the record as the world's longest bony fish, capable of growing up to 8 meters (26 feet). It usually surfaces only by chance, and one such encounter off Sri Lanka marked the first confirmed record of an oarfish in the Indian Ocean, igniting maritime legend and modern science.

The individual, measuring 2.6 m (8.5 ft), was accidentally caught in a surface tuna gillnet set by a multiday fishing vessel off Sri Lanka's west coast. Curious fishers, unfamiliar with the strange catch, brought it ashore at Beruwala Fishery Harbour, where it was handed over to the authorities.

Globally, three species of oarfish are recognized, namely giant oarfish Regalecus glesne), Russell's oarfish (R. russelii) and streamerfish (Agrostichthys parkeri). Detailed examination by Ishara Rathnasuriya of the Ocean University of Sri Lanka confirmed the Sri Lankan specimen as R. russelii. Though collected in 2021, its significance was only recently formalized in a paper published in Acta Ichthyologica et Piscatoria, documenting it as the first oarfish record for the Indian Ocean.

Only a few records of oarfish are scattered over the Indian Ocean and only two specimens have been identified to species level as R. russellii, Rathnasuriya says. The limited observations of R. glesne from the Indian Ocean highlight the importance of the current report, he adds.