News
This study provides new insights and video footage of possibly the largest deep-sea-endemic predatory teleost fish species, the Yokozuna Slickhead, using a combination of eDNA metabarcoding and baited camera observations, at depths of 2000 m. OBIS occurrence data contributed to the distributional comparison of this species to the only other deep-sea-endemic teleost fish species with total length over 2 m, the Giant Grenadier, Albatrossia pectoralis.
Studying life in the deep-sea has challenged researchers to rethink how species from these extreme environments can be detected and studied. As a result, researchers are combining innovative, new methods to overcome the obstacles of detecting species in the deep sea. Deep-sea predators are especially hard to detect, as they are usually not found in groups, but as individuals or small population sizes.
The recently discovered and described Yokozuna Slickhead, Narcetes shonanmaruae, is the largest deep-sea-endemic, bony-fish predator, endemic to Suruga Bay in Japan, occurring at depths surpassing 2,000 m. Detecting this species has proven challenging in the past, as only 6 individuals have ever been collected. With the development of eDNA methods, detecting species in deep-sea environments has become more frequent and successful. eDNA methods effectively provide evidence for the presence of a species in an environment, and is a non-invasive method that does not disturb or restrict the movement or behaviours of animals, which is especially important for biodiversity monitoring in Marine Protected Areas (MPAs). The limitation of eDNA methods is that they cannot provide information regarding the ecology of a species. To overcome this limitation, researchers combine eDNA collection with baited camera observations, which provide essential ecological information of an observed species including possibly its size, sex, population, colourations, behaviour, interactions etc.
In an attempt to advance biodiversity monitoring of deep-sea species in Japan and in particular the Marine Protected Areas, researchers set out on two research cruises during 2020–2021, to six seamounts on the Nishi-Shichito Ridge and the Central and Western Mariana ridges, which are designated as MPAs. Combining metabarcoding analyses of fish and baited camera observations, the team discovered the Yokozuna Slickhead in a previously unrecorded habitat, far away from the type locality of the species. More than 2,600 kg of seawater was filtered, resulting in around 7.8 million denoised reads of fish DNA, acquired through MiSeq sequencing. Reads of Yokozuna Slickhead were detected in seawater samples that were collected at depths of between 1,961–2,060 m, with no detection of this species shallower than 1,900 m.
Sixteen baited camera casts were conducted and a single individual of Yokozuna Slickhead was observed at a depth of 2,091 m at one of the seamounts (bottom figure). Using the video imagery of the baited camera, researchers were also able to observe unexpected threatening behaviour by the Yokozuna Slickhead toward other species, along with a colossal body size estimated at 253 cm. The total length of this individual was much larger than the measurements provided in the original species description. The video footage was also able to reveal the texture of the fish’s parasite infested skin see the Supplemental Video.
The detection of this individual allowed for a distributional comparison to the only other endemic teleost fish species occurring at these depths worldwide and with a size of larger than 2 m, the Giant Grenadier, Albatrossia pectoralis. Authors extracted distribution information of the Giant Grenadier from the OBIS database and compared the occurrence data of the Giant Grenadier to that of the Yokozuna Slickhead (top figure).
This study shows what a powerful tool the combination of eDNA metabarcoding and baited camera observation can be for detecting scarce, predatory fish species in the deep sea. Applying these methods will surely contribute to a better understanding of the distribution and ecology of lesser-known species and vulnerable marine ecosystems in the face of changing global oceans.
Fujiwara Y, Tsuchida S, Kawato M, Masuda K, Sakaguchi SO, Sado T, Miya M, and Yoshida T. (2022). Detection of the largest deep-sea-endemic teleost fish at depths of over 2, 000 m through a combination of eDNA metabarcoding and baited camera observations. Front. Mar. Sci. 9:945758.